merged issue-22

36 files changed, 10671 insertions, 2442 deletions

diff --git a/src/AddressBook/AddressBookProtos.cs b/src/AddressBook/AddressBookProtos.cs
index 9b99452e..1bad0888 100644
--- a/src/AddressBook/AddressBookProtos.cs
+++ b/src/AddressBook/AddressBookProtos.cs
@@ -225,7 +225,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(PhoneNumber prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -235,21 +235,48 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new PhoneNumber();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(PhoneNumber cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

           

-          PhoneNumber result = new PhoneNumber();

+          bool builderIsReadOnly;

+          PhoneNumber result;

+          

+          private PhoneNumber PrepareBuilder() {

+            if (builderIsReadOnly) {

+              PhoneNumber original = result;

+              result = new PhoneNumber();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override PhoneNumber MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new PhoneNumber();

+            result = DefaultInstance ?? new PhoneNumber();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -261,12 +288,11 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
           }

           

           public override PhoneNumber BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            PhoneNumber returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -280,6 +306,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
           

           public override Builder MergeFrom(PhoneNumber other) {

             if (other == global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneNumber.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasNumber) {

               Number = other.Number;

             }

@@ -295,6 +322,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -363,11 +391,13 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
           }

           public Builder SetNumber(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasNumber = true;

             result.number_ = value;

             return this;

           }

           public Builder ClearNumber() {

+            PrepareBuilder();

             result.hasNumber = false;

             result.number_ = "";

             return this;

@@ -381,11 +411,13 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
             set { SetType(value); }

           }

           public Builder SetType(global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneType value) {

+            PrepareBuilder();

             result.hasType = true;

             result.type_ = value;

             return this;

           }

           public Builder ClearType() {

+            PrepareBuilder();

             result.hasType = false;

             result.type_ = global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneType.HOME;

             return this;

@@ -529,7 +561,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(Person prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -539,21 +571,48 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new Person();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(Person cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      Person result = new Person();

+      bool builderIsReadOnly;

+      Person result;

+      

+      private Person PrepareBuilder() {

+        if (builderIsReadOnly) {

+          Person original = result;

+          result = new Person();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override Person MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new Person();

+        result = DefaultInstance ?? new Person();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -565,13 +624,12 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       }

       

       public override Person BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.phone_.MakeReadOnly();

-        Person returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -585,6 +643,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       

       public override Builder MergeFrom(Person other) {

         if (other == global::Google.ProtocolBuffers.Examples.AddressBook.Person.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasName) {

           Name = other.Name;

         }

@@ -606,6 +665,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -674,11 +734,13 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       }

       public Builder SetName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasName = true;

         result.name_ = value;

         return this;

       }

       public Builder ClearName() {

+        PrepareBuilder();

         result.hasName = false;

         result.name_ = "";

         return this;

@@ -692,11 +754,13 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
         set { SetId(value); }

       }

       public Builder SetId(int value) {

+        PrepareBuilder();

         result.hasId = true;

         result.id_ = value;

         return this;

       }

       public Builder ClearId() {

+        PrepareBuilder();

         result.hasId = false;

         result.id_ = 0;

         return this;

@@ -711,18 +775,20 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       }

       public Builder SetEmail(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasEmail = true;

         result.email_ = value;

         return this;

       }

       public Builder ClearEmail() {

+        PrepareBuilder();

         result.hasEmail = false;

         result.email_ = "";

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneNumber> PhoneList {

-        get { return result.phone_; }

+        get { return PrepareBuilder().phone_; }

       }

       public int PhoneCount {

         get { return result.PhoneCount; }

@@ -732,29 +798,35 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       }

       public Builder SetPhone(int index, global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneNumber value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.phone_[index] = value;

         return this;

       }

       public Builder SetPhone(int index, global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneNumber.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.phone_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddPhone(global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneNumber value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.phone_.Add(value);

         return this;

       }

       public Builder AddPhone(global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneNumber.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.phone_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangePhone(scg::IEnumerable<global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneNumber> values) {

+        PrepareBuilder();

         result.phone_.Add(values);

         return this;

       }

       public Builder ClearPhone() {

+        PrepareBuilder();

         result.phone_.Clear();

         return this;

       }

@@ -872,7 +944,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(AddressBook prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -882,21 +954,48 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new AddressBook();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(AddressBook cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      AddressBook result = new AddressBook();

+      bool builderIsReadOnly;

+      AddressBook result;

+      

+      private AddressBook PrepareBuilder() {

+        if (builderIsReadOnly) {

+          AddressBook original = result;

+          result = new AddressBook();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override AddressBook MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new AddressBook();

+        result = DefaultInstance ?? new AddressBook();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -908,13 +1007,12 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       }

       

       public override AddressBook BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.person_.MakeReadOnly();

-        AddressBook returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -928,6 +1026,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       

       public override Builder MergeFrom(AddressBook other) {

         if (other == global::Google.ProtocolBuffers.Examples.AddressBook.AddressBook.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.person_.Count != 0) {

           result.person_.Add(other.person_);

         }

@@ -940,6 +1039,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -988,7 +1088,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.Examples.AddressBook.Person> PersonList {

-        get { return result.person_; }

+        get { return PrepareBuilder().person_; }

       }

       public int PersonCount {

         get { return result.PersonCount; }

@@ -998,29 +1098,35 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       }

       public Builder SetPerson(int index, global::Google.ProtocolBuffers.Examples.AddressBook.Person value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.person_[index] = value;

         return this;

       }

       public Builder SetPerson(int index, global::Google.ProtocolBuffers.Examples.AddressBook.Person.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.person_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddPerson(global::Google.ProtocolBuffers.Examples.AddressBook.Person value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.person_.Add(value);

         return this;

       }

       public Builder AddPerson(global::Google.ProtocolBuffers.Examples.AddressBook.Person.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.person_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangePerson(scg::IEnumerable<global::Google.ProtocolBuffers.Examples.AddressBook.Person> values) {

+        PrepareBuilder();

         result.person_.Add(values);

         return this;

       }

       public Builder ClearPerson() {

+        PrepareBuilder();

         result.person_.Clear();

         return this;

       }

diff --git a/src/ProtoGen/EnumFieldGenerator.cs b/src/ProtoGen/EnumFieldGenerator.cs
index 78384fdd..8d70bc67 100644
--- a/src/ProtoGen/EnumFieldGenerator.cs
+++ b/src/ProtoGen/EnumFieldGenerator.cs
@@ -72,12 +72,14 @@ namespace Google.ProtocolBuffers.ProtoGen
             writer.WriteLine("}");

             AddPublicMemberAttributes(writer);

             writer.WriteLine("public Builder Set{0}({1} value) {{", PropertyName, TypeName);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.has{0} = true;", PropertyName);

             writer.WriteLine("  result.{0}_ = value;", Name);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Clear{0}() {{", PropertyName);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.has{0} = false;", PropertyName);

             writer.WriteLine("  result.{0}_ = {1};", Name, DefaultValue);

             writer.WriteLine("  return this;");

diff --git a/src/ProtoGen/MessageFieldGenerator.cs b/src/ProtoGen/MessageFieldGenerator.cs
index 8e4bef5b..8e2691ee 100644
--- a/src/ProtoGen/MessageFieldGenerator.cs
+++ b/src/ProtoGen/MessageFieldGenerator.cs
@@ -73,6 +73,7 @@ namespace Google.ProtocolBuffers.ProtoGen
             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Set{0}({1} value) {{", PropertyName, TypeName);

             AddNullCheck(writer);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.has{0} = true;", PropertyName);

             writer.WriteLine("  result.{0}_ = value;", Name);

             writer.WriteLine("  return this;");

@@ -80,6 +81,7 @@ namespace Google.ProtocolBuffers.ProtoGen
             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Set{0}({1}.Builder builderForValue) {{", PropertyName, TypeName);

             AddNullCheck(writer, "builderForValue");

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.has{0} = true;", PropertyName);

             writer.WriteLine("  result.{0}_ = builderForValue.Build();", Name);

             writer.WriteLine("  return this;");

@@ -87,6 +89,7 @@ namespace Google.ProtocolBuffers.ProtoGen
             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Merge{0}({1} value) {{", PropertyName, TypeName);

             AddNullCheck(writer);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  if (result.has{0} &&", PropertyName);

             writer.WriteLine("      result.{0}_ != {1}) {{", Name, DefaultValue);

             writer.WriteLine("      result.{0}_ = {1}.CreateBuilder(result.{0}_).MergeFrom(value).BuildPartial();", Name,

@@ -99,6 +102,7 @@ namespace Google.ProtocolBuffers.ProtoGen
             writer.WriteLine("}");

             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Clear{0}() {{", PropertyName);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.has{0} = false;", PropertyName);

             writer.WriteLine("  result.{0}_ = {1};", Name, DefaultValue);

             writer.WriteLine("  return this;");

diff --git a/src/ProtoGen/MessageGenerator.cs b/src/ProtoGen/MessageGenerator.cs
index c8b2087f..89c4aaec 100644
--- a/src/ProtoGen/MessageGenerator.cs
+++ b/src/ProtoGen/MessageGenerator.cs
@@ -556,7 +556,7 @@ namespace Google.ProtocolBuffers.ProtoGen
             writer.WriteLine("public override Builder ToBuilder() { return CreateBuilder(this); }");

             writer.WriteLine("public override Builder CreateBuilderForType() { return new Builder(); }");

             writer.WriteLine("public static Builder CreateBuilder({0} prototype) {{", ClassName);

-            writer.WriteLine("  return (Builder) new Builder().MergeFrom(prototype);");

+            writer.WriteLine("  return new Builder(prototype);");

             writer.WriteLine("}");

             writer.WriteLine();

             if (Descriptor.File.CSharpOptions.AddSerializable)

@@ -591,21 +591,52 @@ namespace Google.ProtocolBuffers.ProtoGen
 

         private void GenerateCommonBuilderMethods(TextGenerator writer)

         {

-            writer.WriteLine("public Builder() {{}}", ClassAccessLevel);

+            //default constructor

+            writer.WriteLine("public Builder() {");

+            //Durring static initialization of message, DefaultInstance is expected to return null.

+            writer.WriteLine("  result = DefaultInstance ?? new {0}();", ClassName);

+            writer.WriteLine("  builderIsReadOnly = result == DefaultInstance;");

+            writer.WriteLine("}");

+            //clone constructor

+            writer.WriteLine("internal Builder({0} cloneFrom) {{", ClassName);

+            writer.WriteLine("  result = cloneFrom;");

+            writer.WriteLine("  builderIsReadOnly = true;");

+            writer.WriteLine("}");

+            writer.WriteLine();

+            writer.WriteLine("bool builderIsReadOnly;");

+            writer.WriteLine("{0} result;", ClassName);

+            writer.WriteLine();

+            writer.WriteLine("private {0} PrepareBuilder() {{", ClassName);

+            writer.WriteLine("  if (builderIsReadOnly) {");

+            writer.WriteLine("    {0} original = result;", ClassName);

+            writer.WriteLine("    result = new {0}();", ClassName);

+            writer.WriteLine("    builderIsReadOnly = false;");

+            writer.WriteLine("    MergeFrom(original);");

+            writer.WriteLine("  }");

+            writer.WriteLine("  return result;");

+            writer.WriteLine("}");

             writer.WriteLine();

-            writer.WriteLine("{0} result = new {0}();", ClassName);

+            writer.WriteLine("public override bool IsInitialized {");

+            writer.WriteLine("  get { return result.IsInitialized; }");

+            writer.WriteLine("}");

             writer.WriteLine();

             writer.WriteLine("protected override {0} MessageBeingBuilt {{", ClassName);

-            writer.WriteLine("  get { return result; }");

+            writer.WriteLine("  get { return PrepareBuilder(); }");

             writer.WriteLine("}");

             writer.WriteLine();

+            //Not actually expecting that DefaultInstance would ever be null here; however, we will ensure it does not break

             writer.WriteLine("public override Builder Clear() {");

-            writer.WriteLine("  result = new {0}();", ClassName);

+            writer.WriteLine("  result = DefaultInstance ?? new {0}();", ClassName);

+            writer.WriteLine("  builderIsReadOnly = true;");

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

             writer.WriteLine();

             writer.WriteLine("public override Builder Clone() {");

-            writer.WriteLine("  return new Builder().MergeFrom(result);");

+            writer.WriteLine("  if (builderIsReadOnly) {");

+            writer.WriteLine("    return new Builder(result);");

+            writer.WriteLine("  } else {");

+            writer.WriteLine("    return new Builder().MergeFrom(result);");

+            writer.WriteLine("  }");

             writer.WriteLine("}");

             writer.WriteLine();

             if (!UseLiteRuntime)

@@ -622,17 +653,15 @@ namespace Google.ProtocolBuffers.ProtoGen
 

             writer.WriteLine("public override {0} BuildPartial() {{", ClassName);

             writer.Indent();

-            writer.WriteLine("if (result == null) {");

-            writer.WriteLine(

-                "  throw new global::System.InvalidOperationException(\"build() has already been called on this Builder\");");

+            writer.WriteLine("if (builderIsReadOnly) {");

+            writer.WriteLine("  return result;");

             writer.WriteLine("}");

             foreach (FieldDescriptor field in Descriptor.Fields)

             {

                 CreateFieldGenerator(field).GenerateBuildingCode(writer);

             }

-            writer.WriteLine("{0} returnMe = result;", ClassName);

-            writer.WriteLine("result = null;");

-            writer.WriteLine("return returnMe;");

+            writer.WriteLine("builderIsReadOnly = true;");

+            writer.WriteLine("return result;");

             writer.Outdent();

             writer.WriteLine("}");

             writer.WriteLine();

@@ -653,6 +682,7 @@ namespace Google.ProtocolBuffers.ProtoGen
                 // fields are set so we can skip the merge.

                 writer.Indent();

                 writer.WriteLine("if (other == {0}.DefaultInstance) return this;", FullClassName);

+                writer.WriteLine("PrepareBuilder();");

                 foreach (FieldDescriptor field in Descriptor.Fields)

                 {

                     CreateFieldGenerator(field).GenerateMergingCode(writer);

@@ -685,6 +715,7 @@ namespace Google.ProtocolBuffers.ProtoGen
             writer.WriteLine(

                 "public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {");

             writer.Indent();

+            writer.WriteLine("PrepareBuilder();");

             if (!UseLiteRuntime)

             {

                 writer.WriteLine("pb::UnknownFieldSet.Builder unknownFields = null;");

diff --git a/src/ProtoGen/PrimitiveFieldGenerator.cs b/src/ProtoGen/PrimitiveFieldGenerator.cs
index 0904ce22..69e0d4d9 100644
--- a/src/ProtoGen/PrimitiveFieldGenerator.cs
+++ b/src/ProtoGen/PrimitiveFieldGenerator.cs
@@ -74,12 +74,14 @@ namespace Google.ProtocolBuffers.ProtoGen
             AddPublicMemberAttributes(writer);

             writer.WriteLine("public Builder Set{0}({1} value) {{", PropertyName, TypeName);

             AddNullCheck(writer);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.has{0} = true;", PropertyName);

             writer.WriteLine("  result.{0}_ = value;", Name);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Clear{0}() {{", PropertyName);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.has{0} = false;", PropertyName);

             writer.WriteLine("  result.{0}_ = {1};", Name, DefaultValue);

             writer.WriteLine("  return this;");

diff --git a/src/ProtoGen/RepeatedEnumFieldGenerator.cs b/src/ProtoGen/RepeatedEnumFieldGenerator.cs
index fcda6564..aacee937 100644
--- a/src/ProtoGen/RepeatedEnumFieldGenerator.cs
+++ b/src/ProtoGen/RepeatedEnumFieldGenerator.cs
@@ -75,7 +75,7 @@ namespace Google.ProtocolBuffers.ProtoGen
             // We return it via IPopsicleList so that collection initializers work more pleasantly.

             AddDeprecatedFlag(writer);

             writer.WriteLine("public pbc::IPopsicleList<{0}> {1}List {{", TypeName, PropertyName);

-            writer.WriteLine("  get {{ return result.{0}_; }}", Name);

+            writer.WriteLine("  get {{ return PrepareBuilder().{0}_; }}", Name);

             writer.WriteLine("}");

             AddDeprecatedFlag(writer);

             writer.WriteLine("public int {0}Count {{", PropertyName);

@@ -87,21 +87,25 @@ namespace Google.ProtocolBuffers.ProtoGen
             writer.WriteLine("}");

             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Set{0}(int index, {1} value) {{", PropertyName, TypeName);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.{0}_[index] = value;", Name);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Add{0}({1} value) {{", PropertyName, TypeName);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.{0}_.Add(value);", Name, TypeName);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder AddRange{0}(scg::IEnumerable<{1}> values) {{", PropertyName, TypeName);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.{0}_.Add(values);", Name);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Clear{0}() {{", PropertyName);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.{0}_.Clear();", Name);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

diff --git a/src/ProtoGen/RepeatedMessageFieldGenerator.cs b/src/ProtoGen/RepeatedMessageFieldGenerator.cs
index d8f0a8eb..6cc1e631 100644
--- a/src/ProtoGen/RepeatedMessageFieldGenerator.cs
+++ b/src/ProtoGen/RepeatedMessageFieldGenerator.cs
@@ -71,7 +71,7 @@ namespace Google.ProtocolBuffers.ProtoGen
             // We return it via IPopsicleList so that collection initializers work more pleasantly.

             AddDeprecatedFlag(writer);

             writer.WriteLine("public pbc::IPopsicleList<{0}> {1}List {{", TypeName, PropertyName);

-            writer.WriteLine("  get {{ return result.{0}_; }}", Name);

+            writer.WriteLine("  get {{ return PrepareBuilder().{0}_; }}", Name);

             writer.WriteLine("}");

             AddDeprecatedFlag(writer);

             writer.WriteLine("public int {0}Count {{", PropertyName);

@@ -84,6 +84,7 @@ namespace Google.ProtocolBuffers.ProtoGen
             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Set{0}(int index, {1} value) {{", PropertyName, TypeName);

             AddNullCheck(writer);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.{0}_[index] = value;", Name);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

@@ -91,12 +92,14 @@ namespace Google.ProtocolBuffers.ProtoGen
             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Set{0}(int index, {1}.Builder builderForValue) {{", PropertyName, TypeName);

             AddNullCheck(writer, "builderForValue");

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.{0}_[index] = builderForValue.Build();", Name);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Add{0}({1} value) {{", PropertyName, TypeName);

             AddNullCheck(writer);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.{0}_.Add(value);", Name, TypeName);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

@@ -104,16 +107,19 @@ namespace Google.ProtocolBuffers.ProtoGen
             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Add{0}({1}.Builder builderForValue) {{", PropertyName, TypeName);

             AddNullCheck(writer, "builderForValue");

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.{0}_.Add(builderForValue.Build());", Name);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder AddRange{0}(scg::IEnumerable<{1}> values) {{", PropertyName, TypeName);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.{0}_.Add(values);", Name);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Clear{0}() {{", PropertyName);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.{0}_.Clear();", Name);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

diff --git a/src/ProtoGen/RepeatedPrimitiveFieldGenerator.cs b/src/ProtoGen/RepeatedPrimitiveFieldGenerator.cs
index 33f0fa2b..645dce5c 100644
--- a/src/ProtoGen/RepeatedPrimitiveFieldGenerator.cs
+++ b/src/ProtoGen/RepeatedPrimitiveFieldGenerator.cs
@@ -75,7 +75,7 @@ namespace Google.ProtocolBuffers.ProtoGen
             // We return it via IPopsicleList so that collection initializers work more pleasantly.

             AddPublicMemberAttributes(writer);

             writer.WriteLine("public pbc::IPopsicleList<{0}> {1}List {{", TypeName, PropertyName);

-            writer.WriteLine("  get {{ return result.{0}_; }}", Name);

+            writer.WriteLine("  get {{ return PrepareBuilder().{0}_; }}", Name);

             writer.WriteLine("}");

             AddDeprecatedFlag(writer);

             writer.WriteLine("public int {0}Count {{", PropertyName);

@@ -88,22 +88,26 @@ namespace Google.ProtocolBuffers.ProtoGen
             AddPublicMemberAttributes(writer);

             writer.WriteLine("public Builder Set{0}(int index, {1} value) {{", PropertyName, TypeName);

             AddNullCheck(writer);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.{0}_[index] = value;", Name);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

             AddPublicMemberAttributes(writer);

             writer.WriteLine("public Builder Add{0}({1} value) {{", PropertyName, TypeName);

             AddNullCheck(writer);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.{0}_.Add(value);", Name, TypeName);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

             AddPublicMemberAttributes(writer);

             writer.WriteLine("public Builder AddRange{0}(scg::IEnumerable<{1}> values) {{", PropertyName, TypeName);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.{0}_.Add(values);", Name);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

             AddDeprecatedFlag(writer);

             writer.WriteLine("public Builder Clear{0}() {{", PropertyName);

+            writer.WriteLine("  PrepareBuilder();");

             writer.WriteLine("  result.{0}_.Clear();", Name);

             writer.WriteLine("  return this;");

             writer.WriteLine("}");

diff --git a/src/ProtocolBuffers.Test/GeneratedMessageTest.cs b/src/ProtocolBuffers.Test/GeneratedMessageTest.cs
index 410452d3..12224e9b 100644
--- a/src/ProtocolBuffers.Test/GeneratedMessageTest.cs
+++ b/src/ProtocolBuffers.Test/GeneratedMessageTest.cs
@@ -112,22 +112,6 @@ namespace Google.ProtocolBuffers
         }

 

         [Test]

-        public void DoubleBuildError()

-        {

-            TestAllTypes.Builder builder = new TestAllTypes.Builder();

-            builder.Build();

-            try

-            {

-                builder.Build();

-                Assert.Fail("Should have thrown exception.");

-            }

-            catch (InvalidOperationException)

-            {

-                // Success.

-            }

-        }

-

-        [Test]

         public void DefaultInstance()

         {

             Assert.AreSame(TestAllTypes.DefaultInstance, TestAllTypes.DefaultInstance.DefaultInstanceForType);

diff --git a/src/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj b/src/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj
index d447db48..83d2ff5b 100644
--- a/src/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj
+++ b/src/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj
@@ -103,6 +103,7 @@
     <Compile Include="NameHelpersTest.cs" />

     <Compile Include="Properties\AssemblyInfo.cs" />

     <Compile Include="ReflectionTester.cs" />

+    <Compile Include="ReusableBuilderTest.cs" />

     <Compile Include="SerializableTest.cs" />

     <Compile Include="ServiceTest.cs" />

     <Compile Include="TestCornerCases.cs" />

diff --git a/src/ProtocolBuffers.Test/ReusableBuilderTest.cs b/src/ProtocolBuffers.Test/ReusableBuilderTest.cs
new file mode 100644
index 00000000..194313cb
--- /dev/null
+++ b/src/ProtocolBuffers.Test/ReusableBuilderTest.cs
@@ -0,0 +1,157 @@
+using System;

+using System.Collections.Generic;

+using System.Text;

+using Google.ProtocolBuffers.Collections;

+using NUnit.Framework;

+using Google.ProtocolBuffers.TestProtos;

+using Google.ProtocolBuffers.Serialization;

+

+namespace Google.ProtocolBuffers

+{

+    [TestFixture]

+    public class ReusableBuilderTest

+    {

+        [Test]

+        public void TestModifyDefaultInstance()

+        {

+            //verify that the default instance has correctly been marked as read-only

+            Assert.AreEqual(typeof(PopsicleList<bool>), TestAllTypes.DefaultInstance.RepeatedBoolList.GetType());

+            PopsicleList<bool> list = (PopsicleList<bool>)TestAllTypes.DefaultInstance.RepeatedBoolList;

+            Assert.IsTrue(list.IsReadOnly);

+        }

+

+        [Test]

+        public void TestUnmodifiedDefaultInstance()

+        {

+            //Simply calling ToBuilder().Build() no longer creates a copy of the message

+            TestAllTypes.Builder builder = TestAllTypes.DefaultInstance.ToBuilder();

+            Assert.IsTrue(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+        }

+

+        [Test]

+        public void BuildMultipleWithoutChange()

+        {

+            //Calling Build() or BuildPartial() does not require a copy of the message

+            TestAllTypes.Builder builder = TestAllTypes.DefaultInstance.ToBuilder();

+            builder.SetDefaultBool(true);

+

+            TestAllTypes first = builder.BuildPartial();

+            //Still the same instance?

+            Assert.IsTrue(ReferenceEquals(first, builder.Build()));

+            //Still the same instance?

+            Assert.IsTrue(ReferenceEquals(first, builder.BuildPartial().ToBuilder().Build()));

+        }

+

+        [Test]

+        public void MergeFromDefaultInstance()

+        {

+            TestAllTypes.Builder builder = TestAllTypes.DefaultInstance.ToBuilder();

+            Assert.IsTrue(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+            builder.MergeFrom(TestAllTypes.DefaultInstance);

+            Assert.IsTrue(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+        }

+

+        [Test]

+        public void BuildNewBuilderIsDefaultInstance()

+        {

+            Assert.IsTrue(ReferenceEquals(TestAllTypes.DefaultInstance, new TestAllTypes.Builder().Build()));

+            Assert.IsTrue(ReferenceEquals(TestAllTypes.DefaultInstance, TestAllTypes.CreateBuilder().Build()));

+            //last test, if you clear a builder it reverts to default instance

+            Assert.IsTrue(ReferenceEquals(TestAllTypes.DefaultInstance,

+                TestAllTypes.CreateBuilder().SetOptionalBool(true).Build().ToBuilder().Clear().Build()));

+        }

+

+        [Test]

+        public void BuildModifyAndRebuild()

+        {

+            TestAllTypes.Builder b1 = new TestAllTypes.Builder();

+            b1.SetDefaultInt32(1);

+            b1.AddRepeatedInt32(2);

+            b1.SetOptionalForeignMessage(ForeignMessage.DefaultInstance);

+

+            TestAllTypes m1 = b1.Build();

+

+            b1.SetDefaultInt32(5);

+            b1.AddRepeatedInt32(6);

+            b1.SetOptionalForeignMessage(b1.OptionalForeignMessage.ToBuilder().SetC(7));

+

+            TestAllTypes m2 = b1.Build();

+            

+            Assert.AreEqual("{\"optional_foreign_message\":{},\"repeated_int32\":[2],\"default_int32\":1}", m1.ToJson());

+            Assert.AreEqual("{\"optional_foreign_message\":{\"c\":7},\"repeated_int32\":[2,6],\"default_int32\":5}", m2.ToJson());

+        }

+

+        [Test]

+        public void CloneOnChangePrimitive()

+        {

+            TestAllTypes.Builder builder = TestAllTypes.DefaultInstance.ToBuilder();

+            Assert.IsTrue(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+            builder.SetDefaultBool(true);

+            Assert.IsFalse(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+        }

+

+        [Test]

+        public void CloneOnAddRepeatedBool()

+        {

+            TestAllTypes.Builder builder = TestAllTypes.DefaultInstance.ToBuilder();

+            Assert.IsTrue(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+            builder.AddRepeatedBool(true);

+            Assert.IsFalse(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+        }

+

+        [Test]

+        public void CloneOnGetRepeatedBoolList()

+        {

+            TestAllTypes.Builder builder = TestAllTypes.DefaultInstance.ToBuilder();

+            Assert.IsTrue(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+            GC.KeepAlive(builder.RepeatedBoolList);

+            Assert.IsFalse(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+        }

+

+        [Test]

+        public void CloneOnChangeMessage()

+        {

+            TestAllTypes.Builder builder = TestAllTypes.DefaultInstance.ToBuilder();

+            Assert.IsTrue(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+            builder.SetOptionalForeignMessage(new ForeignMessage.Builder());

+            Assert.IsFalse(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+        }

+

+        [Test]

+        public void CloneOnClearMessage()

+        {

+            TestAllTypes.Builder builder = TestAllTypes.DefaultInstance.ToBuilder();

+            Assert.IsTrue(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+            builder.ClearOptionalForeignMessage();

+            Assert.IsFalse(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+        }

+

+        [Test]

+        public void CloneOnGetRepeatedForeignMessageList()

+        {

+            TestAllTypes.Builder builder = TestAllTypes.DefaultInstance.ToBuilder();

+            Assert.IsTrue(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+            GC.KeepAlive(builder.RepeatedForeignMessageList);

+            Assert.IsFalse(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+        }

+

+        [Test]

+        public void CloneOnChangeEnumValue()

+        {

+            TestAllTypes.Builder builder = TestAllTypes.DefaultInstance.ToBuilder();

+            Assert.IsTrue(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+            builder.SetOptionalForeignEnum(ForeignEnum.FOREIGN_BAR);

+            Assert.IsFalse(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+        }

+

+        [Test]

+        public void CloneOnGetRepeatedForeignEnumList()

+        {

+            TestAllTypes.Builder builder = TestAllTypes.DefaultInstance.ToBuilder();

+            Assert.IsTrue(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+            GC.KeepAlive(builder.RepeatedForeignEnumList);

+            Assert.IsFalse(ReferenceEquals(TestAllTypes.DefaultInstance, builder.Build()));

+        }

+

+    }

+}

diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestCSharpOptionsProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestCSharpOptionsProtoFile.cs
index 565dc1d0..94ced3d5 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestCSharpOptionsProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestCSharpOptionsProtoFile.cs
@@ -191,7 +191,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(OptionsMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -201,21 +201,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new OptionsMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(OptionsMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      OptionsMessage result;

       

-      OptionsMessage result = new OptionsMessage();

+      private OptionsMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          OptionsMessage original = result;

+          result = new OptionsMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override OptionsMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new OptionsMessage();

+        result = DefaultInstance ?? new OptionsMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -227,12 +254,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override OptionsMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        OptionsMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -246,6 +272,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(OptionsMessage other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.OptionsMessage.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasNormal) {

           Normal = other.Normal;

         }

@@ -264,6 +291,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -328,11 +356,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetNormal(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasNormal = true;

         result.normal_ = value;

         return this;

       }

       public Builder ClearNormal() {

+        PrepareBuilder();

         result.hasNormal = false;

         result.normal_ = "";

         return this;

@@ -347,11 +377,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionsMessage_(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionsMessage_ = true;

         result.optionsMessage_ = value;

         return this;

       }

       public Builder ClearOptionsMessage_() {

+        PrepareBuilder();

         result.hasOptionsMessage_ = false;

         result.optionsMessage_ = "";

         return this;

@@ -366,11 +398,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetCustomName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasCustomName = true;

         result.customized_ = value;

         return this;

       }

       public Builder ClearCustomName() {

+        PrepareBuilder();

         result.hasCustomName = false;

         result.customized_ = "";

         return this;

diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestCustomOptionsProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestCustomOptionsProtoFile.cs
index fc22c716..a3265da7 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestCustomOptionsProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestCustomOptionsProtoFile.cs
@@ -514,7 +514,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestMessageWithCustomOptions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -524,21 +524,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestMessageWithCustomOptions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestMessageWithCustomOptions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestMessageWithCustomOptions result;

+      

+      private TestMessageWithCustomOptions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestMessageWithCustomOptions original = result;

+          result = new TestMessageWithCustomOptions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestMessageWithCustomOptions result = new TestMessageWithCustomOptions();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestMessageWithCustomOptions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestMessageWithCustomOptions();

+        result = DefaultInstance ?? new TestMessageWithCustomOptions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -550,12 +577,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestMessageWithCustomOptions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestMessageWithCustomOptions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -569,6 +595,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestMessageWithCustomOptions other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestMessageWithCustomOptions.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasField1) {

           Field1 = other.Field1;

         }

@@ -581,6 +608,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -637,11 +665,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField1(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField1 = true;

         result.field1_ = value;

         return this;

       }

       public Builder ClearField1() {

+        PrepareBuilder();

         result.hasField1 = false;

         result.field1_ = "";

         return this;

@@ -739,7 +769,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(CustomOptionFooRequest prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -749,21 +779,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new CustomOptionFooRequest();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(CustomOptionFooRequest cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      CustomOptionFooRequest result;

+      

+      private CustomOptionFooRequest PrepareBuilder() {

+        if (builderIsReadOnly) {

+          CustomOptionFooRequest original = result;

+          result = new CustomOptionFooRequest();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      CustomOptionFooRequest result = new CustomOptionFooRequest();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override CustomOptionFooRequest MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new CustomOptionFooRequest();

+        result = DefaultInstance ?? new CustomOptionFooRequest();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -775,12 +832,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override CustomOptionFooRequest BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        CustomOptionFooRequest returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -794,6 +850,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(CustomOptionFooRequest other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.CustomOptionFooRequest.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -803,6 +860,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -938,7 +996,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(CustomOptionFooResponse prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -948,21 +1006,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new CustomOptionFooResponse();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(CustomOptionFooResponse cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      CustomOptionFooResponse result = new CustomOptionFooResponse();

+      bool builderIsReadOnly;

+      CustomOptionFooResponse result;

+      

+      private CustomOptionFooResponse PrepareBuilder() {

+        if (builderIsReadOnly) {

+          CustomOptionFooResponse original = result;

+          result = new CustomOptionFooResponse();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override CustomOptionFooResponse MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new CustomOptionFooResponse();

+        result = DefaultInstance ?? new CustomOptionFooResponse();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -974,12 +1059,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override CustomOptionFooResponse BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        CustomOptionFooResponse returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -993,6 +1077,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(CustomOptionFooResponse other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.CustomOptionFooResponse.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -1002,6 +1087,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1152,7 +1238,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(DummyMessageContainingEnum prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1162,21 +1248,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new DummyMessageContainingEnum();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(DummyMessageContainingEnum cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      DummyMessageContainingEnum result = new DummyMessageContainingEnum();

+      bool builderIsReadOnly;

+      DummyMessageContainingEnum result;

+      

+      private DummyMessageContainingEnum PrepareBuilder() {

+        if (builderIsReadOnly) {

+          DummyMessageContainingEnum original = result;

+          result = new DummyMessageContainingEnum();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override DummyMessageContainingEnum MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new DummyMessageContainingEnum();

+        result = DefaultInstance ?? new DummyMessageContainingEnum();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1188,12 +1301,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override DummyMessageContainingEnum BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        DummyMessageContainingEnum returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1207,6 +1319,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(DummyMessageContainingEnum other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.DummyMessageContainingEnum.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -1216,6 +1329,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1351,7 +1465,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(DummyMessageInvalidAsOptionType prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1361,21 +1475,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new DummyMessageInvalidAsOptionType();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(DummyMessageInvalidAsOptionType cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      DummyMessageInvalidAsOptionType result = new DummyMessageInvalidAsOptionType();

+      bool builderIsReadOnly;

+      DummyMessageInvalidAsOptionType result;

+      

+      private DummyMessageInvalidAsOptionType PrepareBuilder() {

+        if (builderIsReadOnly) {

+          DummyMessageInvalidAsOptionType original = result;

+          result = new DummyMessageInvalidAsOptionType();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override DummyMessageInvalidAsOptionType MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new DummyMessageInvalidAsOptionType();

+        result = DefaultInstance ?? new DummyMessageInvalidAsOptionType();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1387,12 +1528,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override DummyMessageInvalidAsOptionType BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        DummyMessageInvalidAsOptionType returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1406,6 +1546,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(DummyMessageInvalidAsOptionType other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.DummyMessageInvalidAsOptionType.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -1415,6 +1556,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1550,7 +1692,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(CustomOptionMinIntegerValues prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1560,21 +1702,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new CustomOptionMinIntegerValues();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(CustomOptionMinIntegerValues cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      CustomOptionMinIntegerValues result = new CustomOptionMinIntegerValues();

+      bool builderIsReadOnly;

+      CustomOptionMinIntegerValues result;

+      

+      private CustomOptionMinIntegerValues PrepareBuilder() {

+        if (builderIsReadOnly) {

+          CustomOptionMinIntegerValues original = result;

+          result = new CustomOptionMinIntegerValues();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override CustomOptionMinIntegerValues MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new CustomOptionMinIntegerValues();

+        result = DefaultInstance ?? new CustomOptionMinIntegerValues();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1586,12 +1755,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override CustomOptionMinIntegerValues BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        CustomOptionMinIntegerValues returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1605,6 +1773,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(CustomOptionMinIntegerValues other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.CustomOptionMinIntegerValues.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -1614,6 +1783,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1749,7 +1919,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(CustomOptionMaxIntegerValues prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1759,21 +1929,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new CustomOptionMaxIntegerValues();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(CustomOptionMaxIntegerValues cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      CustomOptionMaxIntegerValues result;

+      

+      private CustomOptionMaxIntegerValues PrepareBuilder() {

+        if (builderIsReadOnly) {

+          CustomOptionMaxIntegerValues original = result;

+          result = new CustomOptionMaxIntegerValues();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      CustomOptionMaxIntegerValues result = new CustomOptionMaxIntegerValues();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override CustomOptionMaxIntegerValues MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new CustomOptionMaxIntegerValues();

+        result = DefaultInstance ?? new CustomOptionMaxIntegerValues();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1785,12 +1982,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override CustomOptionMaxIntegerValues BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        CustomOptionMaxIntegerValues returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1804,6 +2000,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(CustomOptionMaxIntegerValues other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.CustomOptionMaxIntegerValues.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -1813,6 +2010,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1948,7 +2146,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(CustomOptionOtherValues prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1958,21 +2156,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new CustomOptionOtherValues();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(CustomOptionOtherValues cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      CustomOptionOtherValues result;

       

-      CustomOptionOtherValues result = new CustomOptionOtherValues();

+      private CustomOptionOtherValues PrepareBuilder() {

+        if (builderIsReadOnly) {

+          CustomOptionOtherValues original = result;

+          result = new CustomOptionOtherValues();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override CustomOptionOtherValues MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new CustomOptionOtherValues();

+        result = DefaultInstance ?? new CustomOptionOtherValues();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1984,12 +2209,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override CustomOptionOtherValues BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        CustomOptionOtherValues returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -2003,6 +2227,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(CustomOptionOtherValues other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.CustomOptionOtherValues.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -2012,6 +2237,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -2147,7 +2373,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(SettingRealsFromPositiveInts prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -2157,21 +2383,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new SettingRealsFromPositiveInts();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(SettingRealsFromPositiveInts cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      SettingRealsFromPositiveInts result;

       

-      SettingRealsFromPositiveInts result = new SettingRealsFromPositiveInts();

+      private SettingRealsFromPositiveInts PrepareBuilder() {

+        if (builderIsReadOnly) {

+          SettingRealsFromPositiveInts original = result;

+          result = new SettingRealsFromPositiveInts();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override SettingRealsFromPositiveInts MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new SettingRealsFromPositiveInts();

+        result = DefaultInstance ?? new SettingRealsFromPositiveInts();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -2183,12 +2436,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override SettingRealsFromPositiveInts BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        SettingRealsFromPositiveInts returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -2202,6 +2454,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(SettingRealsFromPositiveInts other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.SettingRealsFromPositiveInts.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -2211,6 +2464,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -2346,7 +2600,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(SettingRealsFromNegativeInts prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -2356,21 +2610,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new SettingRealsFromNegativeInts();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(SettingRealsFromNegativeInts cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      SettingRealsFromNegativeInts result = new SettingRealsFromNegativeInts();

+      bool builderIsReadOnly;

+      SettingRealsFromNegativeInts result;

+      

+      private SettingRealsFromNegativeInts PrepareBuilder() {

+        if (builderIsReadOnly) {

+          SettingRealsFromNegativeInts original = result;

+          result = new SettingRealsFromNegativeInts();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override SettingRealsFromNegativeInts MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new SettingRealsFromNegativeInts();

+        result = DefaultInstance ?? new SettingRealsFromNegativeInts();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -2382,12 +2663,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override SettingRealsFromNegativeInts BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        SettingRealsFromNegativeInts returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -2401,6 +2681,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(SettingRealsFromNegativeInts other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.SettingRealsFromNegativeInts.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -2410,6 +2691,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -2597,7 +2879,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(ComplexOptionType1 prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -2607,21 +2889,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new ComplexOptionType1();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(ComplexOptionType1 cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      ComplexOptionType1 result;

+      

+      private ComplexOptionType1 PrepareBuilder() {

+        if (builderIsReadOnly) {

+          ComplexOptionType1 original = result;

+          result = new ComplexOptionType1();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      ComplexOptionType1 result = new ComplexOptionType1();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override ComplexOptionType1 MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new ComplexOptionType1();

+        result = DefaultInstance ?? new ComplexOptionType1();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -2633,12 +2942,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override ComplexOptionType1 BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        ComplexOptionType1 returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -2652,6 +2960,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(ComplexOptionType1 other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.ComplexOptionType1.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasFoo) {

           Foo = other.Foo;

         }

@@ -2671,6 +2980,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -2734,11 +3044,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetFoo(value); }

       }

       public Builder SetFoo(int value) {

+        PrepareBuilder();

         result.hasFoo = true;

         result.foo_ = value;

         return this;

       }

       public Builder ClearFoo() {

+        PrepareBuilder();

         result.hasFoo = false;

         result.foo_ = 0;

         return this;

@@ -2752,11 +3064,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetFoo2(value); }

       }

       public Builder SetFoo2(int value) {

+        PrepareBuilder();

         result.hasFoo2 = true;

         result.foo2_ = value;

         return this;

       }

       public Builder ClearFoo2() {

+        PrepareBuilder();

         result.hasFoo2 = false;

         result.foo2_ = 0;

         return this;

@@ -2770,11 +3084,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetFoo3(value); }

       }

       public Builder SetFoo3(int value) {

+        PrepareBuilder();

         result.hasFoo3 = true;

         result.foo3_ = value;

         return this;

       }

       public Builder ClearFoo3() {

+        PrepareBuilder();

         result.hasFoo3 = false;

         result.foo3_ = 0;

         return this;

@@ -2923,7 +3239,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(ComplexOptionType4 prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -2933,21 +3249,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new ComplexOptionType4();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(ComplexOptionType4 cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

           

-          ComplexOptionType4 result = new ComplexOptionType4();

+          bool builderIsReadOnly;

+          ComplexOptionType4 result;

+          

+          private ComplexOptionType4 PrepareBuilder() {

+            if (builderIsReadOnly) {

+              ComplexOptionType4 original = result;

+              result = new ComplexOptionType4();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override ComplexOptionType4 MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new ComplexOptionType4();

+            result = DefaultInstance ?? new ComplexOptionType4();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -2959,12 +3302,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override ComplexOptionType4 BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            ComplexOptionType4 returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -2978,6 +3320,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(ComplexOptionType4 other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.ComplexOptionType2.Types.ComplexOptionType4.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasWaldo) {

               Waldo = other.Waldo;

             }

@@ -2990,6 +3333,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -3045,11 +3389,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetWaldo(value); }

           }

           public Builder SetWaldo(int value) {

+            PrepareBuilder();

             result.hasWaldo = true;

             result.waldo_ = value;

             return this;

           }

           public Builder ClearWaldo() {

+            PrepareBuilder();

             result.hasWaldo = false;

             result.waldo_ = 0;

             return this;

@@ -3177,7 +3523,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(ComplexOptionType2 prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -3187,21 +3533,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new ComplexOptionType2();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(ComplexOptionType2 cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      ComplexOptionType2 result;

       

-      ComplexOptionType2 result = new ComplexOptionType2();

+      private ComplexOptionType2 PrepareBuilder() {

+        if (builderIsReadOnly) {

+          ComplexOptionType2 original = result;

+          result = new ComplexOptionType2();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override ComplexOptionType2 MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new ComplexOptionType2();

+        result = DefaultInstance ?? new ComplexOptionType2();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -3213,12 +3586,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override ComplexOptionType2 BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        ComplexOptionType2 returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -3232,6 +3604,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(ComplexOptionType2 other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.ComplexOptionType2.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasBar) {

           MergeBar(other.Bar);

         }

@@ -3251,6 +3624,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -3325,18 +3699,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetBar(global::Google.ProtocolBuffers.TestProtos.ComplexOptionType1 value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasBar = true;

         result.bar_ = value;

         return this;

       }

       public Builder SetBar(global::Google.ProtocolBuffers.TestProtos.ComplexOptionType1.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasBar = true;

         result.bar_ = builderForValue.Build();

         return this;

       }

       public Builder MergeBar(global::Google.ProtocolBuffers.TestProtos.ComplexOptionType1 value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasBar &&

             result.bar_ != global::Google.ProtocolBuffers.TestProtos.ComplexOptionType1.DefaultInstance) {

             result.bar_ = global::Google.ProtocolBuffers.TestProtos.ComplexOptionType1.CreateBuilder(result.bar_).MergeFrom(value).BuildPartial();

@@ -3347,6 +3724,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearBar() {

+        PrepareBuilder();

         result.hasBar = false;

         result.bar_ = global::Google.ProtocolBuffers.TestProtos.ComplexOptionType1.DefaultInstance;

         return this;

@@ -3360,11 +3738,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetBaz(value); }

       }

       public Builder SetBaz(int value) {

+        PrepareBuilder();

         result.hasBaz = true;

         result.baz_ = value;

         return this;

       }

       public Builder ClearBaz() {

+        PrepareBuilder();

         result.hasBaz = false;

         result.baz_ = 0;

         return this;

@@ -3379,18 +3759,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetFred(global::Google.ProtocolBuffers.TestProtos.ComplexOptionType2.Types.ComplexOptionType4 value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasFred = true;

         result.fred_ = value;

         return this;

       }

       public Builder SetFred(global::Google.ProtocolBuffers.TestProtos.ComplexOptionType2.Types.ComplexOptionType4.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasFred = true;

         result.fred_ = builderForValue.Build();

         return this;

       }

       public Builder MergeFred(global::Google.ProtocolBuffers.TestProtos.ComplexOptionType2.Types.ComplexOptionType4 value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasFred &&

             result.fred_ != global::Google.ProtocolBuffers.TestProtos.ComplexOptionType2.Types.ComplexOptionType4.DefaultInstance) {

             result.fred_ = global::Google.ProtocolBuffers.TestProtos.ComplexOptionType2.Types.ComplexOptionType4.CreateBuilder(result.fred_).MergeFrom(value).BuildPartial();

@@ -3401,6 +3784,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearFred() {

+        PrepareBuilder();

         result.hasFred = false;

         result.fred_ = global::Google.ProtocolBuffers.TestProtos.ComplexOptionType2.Types.ComplexOptionType4.DefaultInstance;

         return this;

@@ -3547,7 +3931,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(ComplexOptionType5 prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -3557,21 +3941,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new ComplexOptionType5();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(ComplexOptionType5 cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          ComplexOptionType5 result;

+          

+          private ComplexOptionType5 PrepareBuilder() {

+            if (builderIsReadOnly) {

+              ComplexOptionType5 original = result;

+              result = new ComplexOptionType5();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

           

-          ComplexOptionType5 result = new ComplexOptionType5();

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override ComplexOptionType5 MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new ComplexOptionType5();

+            result = DefaultInstance ?? new ComplexOptionType5();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -3583,12 +3994,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override ComplexOptionType5 BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            ComplexOptionType5 returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -3602,6 +4012,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(ComplexOptionType5 other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.ComplexOptionType3.Types.ComplexOptionType5.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasPlugh) {

               Plugh = other.Plugh;

             }

@@ -3614,6 +4025,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -3669,11 +4081,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetPlugh(value); }

           }

           public Builder SetPlugh(int value) {

+            PrepareBuilder();

             result.hasPlugh = true;

             result.plugh_ = value;

             return this;

           }

           public Builder ClearPlugh() {

+            PrepareBuilder();

             result.hasPlugh = false;

             result.plugh_ = 0;

             return this;

@@ -3778,7 +4192,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(ComplexOptionType3 prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -3788,21 +4202,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new ComplexOptionType3();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(ComplexOptionType3 cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      ComplexOptionType3 result = new ComplexOptionType3();

+      bool builderIsReadOnly;

+      ComplexOptionType3 result;

+      

+      private ComplexOptionType3 PrepareBuilder() {

+        if (builderIsReadOnly) {

+          ComplexOptionType3 original = result;

+          result = new ComplexOptionType3();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override ComplexOptionType3 MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new ComplexOptionType3();

+        result = DefaultInstance ?? new ComplexOptionType3();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -3814,12 +4255,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override ComplexOptionType3 BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        ComplexOptionType3 returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -3833,6 +4273,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(ComplexOptionType3 other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.ComplexOptionType3.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasQux) {

           Qux = other.Qux;

         }

@@ -3848,6 +4289,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -3912,11 +4354,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetQux(value); }

       }

       public Builder SetQux(int value) {

+        PrepareBuilder();

         result.hasQux = true;

         result.qux_ = value;

         return this;

       }

       public Builder ClearQux() {

+        PrepareBuilder();

         result.hasQux = false;

         result.qux_ = 0;

         return this;

@@ -3931,18 +4375,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetComplexOptionType5(global::Google.ProtocolBuffers.TestProtos.ComplexOptionType3.Types.ComplexOptionType5 value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasComplexOptionType5 = true;

         result.complexOptionType5_ = value;

         return this;

       }

       public Builder SetComplexOptionType5(global::Google.ProtocolBuffers.TestProtos.ComplexOptionType3.Types.ComplexOptionType5.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasComplexOptionType5 = true;

         result.complexOptionType5_ = builderForValue.Build();

         return this;

       }

       public Builder MergeComplexOptionType5(global::Google.ProtocolBuffers.TestProtos.ComplexOptionType3.Types.ComplexOptionType5 value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasComplexOptionType5 &&

             result.complexOptionType5_ != global::Google.ProtocolBuffers.TestProtos.ComplexOptionType3.Types.ComplexOptionType5.DefaultInstance) {

             result.complexOptionType5_ = global::Google.ProtocolBuffers.TestProtos.ComplexOptionType3.Types.ComplexOptionType5.CreateBuilder(result.complexOptionType5_).MergeFrom(value).BuildPartial();

@@ -3953,6 +4400,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearComplexOptionType5() {

+        PrepareBuilder();

         result.hasComplexOptionType5 = false;

         result.complexOptionType5_ = global::Google.ProtocolBuffers.TestProtos.ComplexOptionType3.Types.ComplexOptionType5.DefaultInstance;

         return this;

@@ -4066,7 +4514,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(ComplexOpt6 prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -4076,21 +4524,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new ComplexOpt6();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(ComplexOpt6 cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      ComplexOpt6 result;

+      

+      private ComplexOpt6 PrepareBuilder() {

+        if (builderIsReadOnly) {

+          ComplexOpt6 original = result;

+          result = new ComplexOpt6();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      ComplexOpt6 result = new ComplexOpt6();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override ComplexOpt6 MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new ComplexOpt6();

+        result = DefaultInstance ?? new ComplexOpt6();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -4102,12 +4577,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override ComplexOpt6 BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        ComplexOpt6 returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -4121,6 +4595,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(ComplexOpt6 other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.ComplexOpt6.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasXyzzy) {

           Xyzzy = other.Xyzzy;

         }

@@ -4133,6 +4608,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -4188,11 +4664,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetXyzzy(value); }

       }

       public Builder SetXyzzy(int value) {

+        PrepareBuilder();

         result.hasXyzzy = true;

         result.xyzzy_ = value;

         return this;

       }

       public Builder ClearXyzzy() {

+        PrepareBuilder();

         result.hasXyzzy = false;

         result.xyzzy_ = 0;

         return this;

@@ -4290,7 +4768,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(VariousComplexOptions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -4300,21 +4778,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new VariousComplexOptions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(VariousComplexOptions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      VariousComplexOptions result;

       

-      VariousComplexOptions result = new VariousComplexOptions();

+      private VariousComplexOptions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          VariousComplexOptions original = result;

+          result = new VariousComplexOptions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override VariousComplexOptions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new VariousComplexOptions();

+        result = DefaultInstance ?? new VariousComplexOptions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -4326,12 +4831,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override VariousComplexOptions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        VariousComplexOptions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -4345,6 +4849,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(VariousComplexOptions other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.VariousComplexOptions.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -4354,6 +4859,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
index 149f2182..9af43135 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
@@ -187,7 +187,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestEmbedOptimizedForSize prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -197,21 +197,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestEmbedOptimizedForSize();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestEmbedOptimizedForSize cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestEmbedOptimizedForSize result;

       

-      TestEmbedOptimizedForSize result = new TestEmbedOptimizedForSize();

+      private TestEmbedOptimizedForSize PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestEmbedOptimizedForSize original = result;

+          result = new TestEmbedOptimizedForSize();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestEmbedOptimizedForSize MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestEmbedOptimizedForSize();

+        result = DefaultInstance ?? new TestEmbedOptimizedForSize();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -223,13 +250,12 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestEmbedOptimizedForSize BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.repeatedMessage_.MakeReadOnly();

-        TestEmbedOptimizedForSize returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -243,6 +269,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestEmbedOptimizedForSize other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestEmbedOptimizedForSize.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasOptionalMessage) {

           MergeOptionalMessage(other.OptionalMessage);

         }

@@ -258,6 +285,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -323,18 +351,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalMessage(global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalMessage = true;

         result.optionalMessage_ = value;

         return this;

       }

       public Builder SetOptionalMessage(global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalMessage = true;

         result.optionalMessage_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalMessage(global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalMessage &&

             result.optionalMessage_ != global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize.DefaultInstance) {

             result.optionalMessage_ = global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize.CreateBuilder(result.optionalMessage_).MergeFrom(value).BuildPartial();

@@ -345,13 +376,14 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalMessage() {

+        PrepareBuilder();

         result.hasOptionalMessage = false;

         result.optionalMessage_ = global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize.DefaultInstance;

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize> RepeatedMessageList {

-        get { return result.repeatedMessage_; }

+        get { return PrepareBuilder().repeatedMessage_; }

       }

       public int RepeatedMessageCount {

         get { return result.RepeatedMessageCount; }

@@ -361,29 +393,35 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedMessage(int index, global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedMessage_[index] = value;

         return this;

       }

       public Builder SetRepeatedMessage(int index, global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedMessage_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedMessage(global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedMessage_.Add(value);

         return this;

       }

       public Builder AddRepeatedMessage(global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedMessage_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize> values) {

+        PrepareBuilder();

         result.repeatedMessage_.Add(values);

         return this;

       }

       public Builder ClearRepeatedMessage() {

+        PrepareBuilder();

         result.repeatedMessage_.Clear();

         return this;

       }

diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestExtrasIssuesProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestExtrasIssuesProtoFile.cs
index aefa95e1..47841404 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestExtrasIssuesProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestExtrasIssuesProtoFile.cs
@@ -224,7 +224,7 @@ namespace UnitTest.Issues.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(A prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -234,21 +234,48 @@ namespace UnitTest.Issues.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new A();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(A cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      A result;

+      

+      private A PrepareBuilder() {

+        if (builderIsReadOnly) {

+          A original = result;

+          result = new A();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      A result = new A();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override A MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new A();

+        result = DefaultInstance ?? new A();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -260,12 +287,11 @@ namespace UnitTest.Issues.TestProtos {
       }

       

       public override A BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        A returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -279,6 +305,7 @@ namespace UnitTest.Issues.TestProtos {
       

       public override Builder MergeFrom(A other) {

         if (other == global::UnitTest.Issues.TestProtos.A.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA_) {

           A_ = other.A_;

         }

@@ -291,6 +318,7 @@ namespace UnitTest.Issues.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -346,11 +374,13 @@ namespace UnitTest.Issues.TestProtos {
         set { SetA_(value); }

       }

       public Builder SetA_(int value) {

+        PrepareBuilder();

         result.hasA_ = true;

         result.a_ = value;

         return this;

       }

       public Builder ClearA_() {

+        PrepareBuilder();

         result.hasA_ = false;

         result.a_ = 0;

         return this;

@@ -464,7 +494,7 @@ namespace UnitTest.Issues.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(B prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -474,21 +504,48 @@ namespace UnitTest.Issues.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new B();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(B cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      B result;

+      

+      private B PrepareBuilder() {

+        if (builderIsReadOnly) {

+          B original = result;

+          result = new B();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      B result = new B();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override B MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new B();

+        result = DefaultInstance ?? new B();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -500,12 +557,11 @@ namespace UnitTest.Issues.TestProtos {
       }

       

       public override B BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        B returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -519,6 +575,7 @@ namespace UnitTest.Issues.TestProtos {
       

       public override Builder MergeFrom(B other) {

         if (other == global::UnitTest.Issues.TestProtos.B.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasB_) {

           B_ = other.B_;

         }

@@ -531,6 +588,7 @@ namespace UnitTest.Issues.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -586,11 +644,13 @@ namespace UnitTest.Issues.TestProtos {
         set { SetB_(value); }

       }

       public Builder SetB_(int value) {

+        PrepareBuilder();

         result.hasB_ = true;

         result.b_ = value;

         return this;

       }

       public Builder ClearB_() {

+        PrepareBuilder();

         result.hasB_ = false;

         result.b_ = 0;

         return this;

@@ -704,7 +764,7 @@ namespace UnitTest.Issues.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(AB prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -714,21 +774,48 @@ namespace UnitTest.Issues.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new AB();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(AB cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      AB result;

+      

+      private AB PrepareBuilder() {

+        if (builderIsReadOnly) {

+          AB original = result;

+          result = new AB();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      AB result = new AB();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override AB MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new AB();

+        result = DefaultInstance ?? new AB();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -740,12 +827,11 @@ namespace UnitTest.Issues.TestProtos {
       }

       

       public override AB BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        AB returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -759,6 +845,7 @@ namespace UnitTest.Issues.TestProtos {
       

       public override Builder MergeFrom(AB other) {

         if (other == global::UnitTest.Issues.TestProtos.AB.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasAB_) {

           AB_ = other.AB_;

         }

@@ -771,6 +858,7 @@ namespace UnitTest.Issues.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -826,11 +914,13 @@ namespace UnitTest.Issues.TestProtos {
         set { SetAB_(value); }

       }

       public Builder SetAB_(int value) {

+        PrepareBuilder();

         result.hasAB_ = true;

         result.aB_ = value;

         return this;

       }

       public Builder ClearAB_() {

+        PrepareBuilder();

         result.hasAB_ = false;

         result.aB_ = 0;

         return this;

@@ -946,7 +1036,7 @@ namespace UnitTest.Issues.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(NumberField prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -956,21 +1046,48 @@ namespace UnitTest.Issues.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new NumberField();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(NumberField cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      NumberField result;

       

-      NumberField result = new NumberField();

+      private NumberField PrepareBuilder() {

+        if (builderIsReadOnly) {

+          NumberField original = result;

+          result = new NumberField();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override NumberField MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new NumberField();

+        result = DefaultInstance ?? new NumberField();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -982,12 +1099,11 @@ namespace UnitTest.Issues.TestProtos {
       }

       

       public override NumberField BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        NumberField returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1001,6 +1117,7 @@ namespace UnitTest.Issues.TestProtos {
       

       public override Builder MergeFrom(NumberField other) {

         if (other == global::UnitTest.Issues.TestProtos.NumberField.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.Has_01) {

           _01 = other._01;

         }

@@ -1013,6 +1130,7 @@ namespace UnitTest.Issues.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1070,11 +1188,13 @@ namespace UnitTest.Issues.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder Set_01(int value) {

+        PrepareBuilder();

         result.has_01 = true;

         result._01_ = value;

         return this;

       }

       public Builder Clear_01() {

+        PrepareBuilder();

         result.has_01 = false;

         result._01_ = 0;

         return this;

@@ -1241,7 +1361,7 @@ namespace UnitTest.Issues.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(NegativeEnumMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1251,21 +1371,48 @@ namespace UnitTest.Issues.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new NegativeEnumMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(NegativeEnumMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      NegativeEnumMessage result;

+      

+      private NegativeEnumMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          NegativeEnumMessage original = result;

+          result = new NegativeEnumMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      NegativeEnumMessage result = new NegativeEnumMessage();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override NegativeEnumMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new NegativeEnumMessage();

+        result = DefaultInstance ?? new NegativeEnumMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1277,14 +1424,13 @@ namespace UnitTest.Issues.TestProtos {
       }

       

       public override NegativeEnumMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.values_.MakeReadOnly();

         result.packedValues_.MakeReadOnly();

-        NegativeEnumMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1298,6 +1444,7 @@ namespace UnitTest.Issues.TestProtos {
       

       public override Builder MergeFrom(NegativeEnumMessage other) {

         if (other == global::UnitTest.Issues.TestProtos.NegativeEnumMessage.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasValue) {

           Value = other.Value;

         }

@@ -1316,6 +1463,7 @@ namespace UnitTest.Issues.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1407,18 +1555,20 @@ namespace UnitTest.Issues.TestProtos {
         set { SetValue(value); }

       }

       public Builder SetValue(global::UnitTest.Issues.TestProtos.NegativeEnum value) {

+        PrepareBuilder();

         result.hasValue = true;

         result.value_ = value;

         return this;

       }

       public Builder ClearValue() {

+        PrepareBuilder();

         result.hasValue = false;

         result.value_ = global::UnitTest.Issues.TestProtos.NegativeEnum.FiveBelow;

         return this;

       }

       

       public pbc::IPopsicleList<global::UnitTest.Issues.TestProtos.NegativeEnum> ValuesList {

-        get { return result.values_; }

+        get { return PrepareBuilder().values_; }

       }

       public int ValuesCount {

         get { return result.ValuesCount; }

@@ -1427,24 +1577,28 @@ namespace UnitTest.Issues.TestProtos {
         return result.GetValues(index);

       }

       public Builder SetValues(int index, global::UnitTest.Issues.TestProtos.NegativeEnum value) {

+        PrepareBuilder();

         result.values_[index] = value;

         return this;

       }

       public Builder AddValues(global::UnitTest.Issues.TestProtos.NegativeEnum value) {

+        PrepareBuilder();

         result.values_.Add(value);

         return this;

       }

       public Builder AddRangeValues(scg::IEnumerable<global::UnitTest.Issues.TestProtos.NegativeEnum> values) {

+        PrepareBuilder();

         result.values_.Add(values);

         return this;

       }

       public Builder ClearValues() {

+        PrepareBuilder();

         result.values_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::UnitTest.Issues.TestProtos.NegativeEnum> PackedValuesList {

-        get { return result.packedValues_; }

+        get { return PrepareBuilder().packedValues_; }

       }

       public int PackedValuesCount {

         get { return result.PackedValuesCount; }

@@ -1453,18 +1607,22 @@ namespace UnitTest.Issues.TestProtos {
         return result.GetPackedValues(index);

       }

       public Builder SetPackedValues(int index, global::UnitTest.Issues.TestProtos.NegativeEnum value) {

+        PrepareBuilder();

         result.packedValues_[index] = value;

         return this;

       }

       public Builder AddPackedValues(global::UnitTest.Issues.TestProtos.NegativeEnum value) {

+        PrepareBuilder();

         result.packedValues_.Add(value);

         return this;

       }

       public Builder AddRangePackedValues(scg::IEnumerable<global::UnitTest.Issues.TestProtos.NegativeEnum> values) {

+        PrepareBuilder();

         result.packedValues_.Add(values);

         return this;

       }

       public Builder ClearPackedValues() {

+        PrepareBuilder();

         result.packedValues_.Clear();

         return this;

       }

@@ -1561,7 +1719,7 @@ namespace UnitTest.Issues.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(DeprecatedChild prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1571,21 +1729,48 @@ namespace UnitTest.Issues.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new DeprecatedChild();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(DeprecatedChild cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      DeprecatedChild result = new DeprecatedChild();

+      bool builderIsReadOnly;

+      DeprecatedChild result;

+      

+      private DeprecatedChild PrepareBuilder() {

+        if (builderIsReadOnly) {

+          DeprecatedChild original = result;

+          result = new DeprecatedChild();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override DeprecatedChild MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new DeprecatedChild();

+        result = DefaultInstance ?? new DeprecatedChild();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1597,12 +1782,11 @@ namespace UnitTest.Issues.TestProtos {
       }

       

       public override DeprecatedChild BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        DeprecatedChild returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1616,6 +1800,7 @@ namespace UnitTest.Issues.TestProtos {
       

       public override Builder MergeFrom(DeprecatedChild other) {

         if (other == global::UnitTest.Issues.TestProtos.DeprecatedChild.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -1625,6 +1810,7 @@ namespace UnitTest.Issues.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1889,7 +2075,7 @@ namespace UnitTest.Issues.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(DeprecatedFieldsMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1899,21 +2085,48 @@ namespace UnitTest.Issues.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new DeprecatedFieldsMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(DeprecatedFieldsMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      DeprecatedFieldsMessage result = new DeprecatedFieldsMessage();

+      bool builderIsReadOnly;

+      DeprecatedFieldsMessage result;

+      

+      private DeprecatedFieldsMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          DeprecatedFieldsMessage original = result;

+          result = new DeprecatedFieldsMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override DeprecatedFieldsMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new DeprecatedFieldsMessage();

+        result = DefaultInstance ?? new DeprecatedFieldsMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1925,15 +2138,14 @@ namespace UnitTest.Issues.TestProtos {
       }

       

       public override DeprecatedFieldsMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.primitiveArray_.MakeReadOnly();

         result.messageArray_.MakeReadOnly();

         result.enumArray_.MakeReadOnly();

-        DeprecatedFieldsMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1947,6 +2159,7 @@ namespace UnitTest.Issues.TestProtos {
       

       public override Builder MergeFrom(DeprecatedFieldsMessage other) {

         if (other == global::UnitTest.Issues.TestProtos.DeprecatedFieldsMessage.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasPrimitiveValue) {

           PrimitiveValue = other.PrimitiveValue;

         }

@@ -1974,6 +2187,7 @@ namespace UnitTest.Issues.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -2076,12 +2290,14 @@ namespace UnitTest.Issues.TestProtos {
       }

       [global::System.ObsoleteAttribute()]

       public Builder SetPrimitiveValue(int value) {

+        PrepareBuilder();

         result.hasPrimitiveValue = true;

         result.primitiveValue_ = value;

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder ClearPrimitiveValue() {

+        PrepareBuilder();

         result.hasPrimitiveValue = false;

         result.primitiveValue_ = 0;

         return this;

@@ -2089,7 +2305,7 @@ namespace UnitTest.Issues.TestProtos {
       

       [global::System.ObsoleteAttribute()]

       public pbc::IPopsicleList<int> PrimitiveArrayList {

-        get { return result.primitiveArray_; }

+        get { return PrepareBuilder().primitiveArray_; }

       }

       [global::System.ObsoleteAttribute()]

       public int PrimitiveArrayCount {

@@ -2101,21 +2317,25 @@ namespace UnitTest.Issues.TestProtos {
       }

       [global::System.ObsoleteAttribute()]

       public Builder SetPrimitiveArray(int index, int value) {

+        PrepareBuilder();

         result.primitiveArray_[index] = value;

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder AddPrimitiveArray(int value) {

+        PrepareBuilder();

         result.primitiveArray_.Add(value);

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder AddRangePrimitiveArray(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.primitiveArray_.Add(values);

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder ClearPrimitiveArray() {

+        PrepareBuilder();

         result.primitiveArray_.Clear();

         return this;

       }

@@ -2132,6 +2352,7 @@ namespace UnitTest.Issues.TestProtos {
       [global::System.ObsoleteAttribute()]

       public Builder SetMessageValue(global::UnitTest.Issues.TestProtos.DeprecatedChild value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasMessageValue = true;

         result.messageValue_ = value;

         return this;

@@ -2139,6 +2360,7 @@ namespace UnitTest.Issues.TestProtos {
       [global::System.ObsoleteAttribute()]

       public Builder SetMessageValue(global::UnitTest.Issues.TestProtos.DeprecatedChild.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasMessageValue = true;

         result.messageValue_ = builderForValue.Build();

         return this;

@@ -2146,6 +2368,7 @@ namespace UnitTest.Issues.TestProtos {
       [global::System.ObsoleteAttribute()]

       public Builder MergeMessageValue(global::UnitTest.Issues.TestProtos.DeprecatedChild value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasMessageValue &&

             result.messageValue_ != global::UnitTest.Issues.TestProtos.DeprecatedChild.DefaultInstance) {

             result.messageValue_ = global::UnitTest.Issues.TestProtos.DeprecatedChild.CreateBuilder(result.messageValue_).MergeFrom(value).BuildPartial();

@@ -2157,6 +2380,7 @@ namespace UnitTest.Issues.TestProtos {
       }

       [global::System.ObsoleteAttribute()]

       public Builder ClearMessageValue() {

+        PrepareBuilder();

         result.hasMessageValue = false;

         result.messageValue_ = global::UnitTest.Issues.TestProtos.DeprecatedChild.DefaultInstance;

         return this;

@@ -2164,7 +2388,7 @@ namespace UnitTest.Issues.TestProtos {
       

       [global::System.ObsoleteAttribute()]

       public pbc::IPopsicleList<global::UnitTest.Issues.TestProtos.DeprecatedChild> MessageArrayList {

-        get { return result.messageArray_; }

+        get { return PrepareBuilder().messageArray_; }

       }

       [global::System.ObsoleteAttribute()]

       public int MessageArrayCount {

@@ -2177,34 +2401,40 @@ namespace UnitTest.Issues.TestProtos {
       [global::System.ObsoleteAttribute()]

       public Builder SetMessageArray(int index, global::UnitTest.Issues.TestProtos.DeprecatedChild value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.messageArray_[index] = value;

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder SetMessageArray(int index, global::UnitTest.Issues.TestProtos.DeprecatedChild.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.messageArray_[index] = builderForValue.Build();

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder AddMessageArray(global::UnitTest.Issues.TestProtos.DeprecatedChild value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.messageArray_.Add(value);

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder AddMessageArray(global::UnitTest.Issues.TestProtos.DeprecatedChild.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.messageArray_.Add(builderForValue.Build());

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder AddRangeMessageArray(scg::IEnumerable<global::UnitTest.Issues.TestProtos.DeprecatedChild> values) {

+        PrepareBuilder();

         result.messageArray_.Add(values);

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder ClearMessageArray() {

+        PrepareBuilder();

         result.messageArray_.Clear();

         return this;

       }

@@ -2220,12 +2450,14 @@ namespace UnitTest.Issues.TestProtos {
       }

       [global::System.ObsoleteAttribute()]

       public Builder SetEnumValue(global::UnitTest.Issues.TestProtos.DeprecatedEnum value) {

+        PrepareBuilder();

         result.hasEnumValue = true;

         result.enumValue_ = value;

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder ClearEnumValue() {

+        PrepareBuilder();

         result.hasEnumValue = false;

         result.enumValue_ = global::UnitTest.Issues.TestProtos.DeprecatedEnum.one;

         return this;

@@ -2233,7 +2465,7 @@ namespace UnitTest.Issues.TestProtos {
       

       [global::System.ObsoleteAttribute()]

       public pbc::IPopsicleList<global::UnitTest.Issues.TestProtos.DeprecatedEnum> EnumArrayList {

-        get { return result.enumArray_; }

+        get { return PrepareBuilder().enumArray_; }

       }

       [global::System.ObsoleteAttribute()]

       public int EnumArrayCount {

@@ -2245,21 +2477,25 @@ namespace UnitTest.Issues.TestProtos {
       }

       [global::System.ObsoleteAttribute()]

       public Builder SetEnumArray(int index, global::UnitTest.Issues.TestProtos.DeprecatedEnum value) {

+        PrepareBuilder();

         result.enumArray_[index] = value;

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder AddEnumArray(global::UnitTest.Issues.TestProtos.DeprecatedEnum value) {

+        PrepareBuilder();

         result.enumArray_.Add(value);

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder AddRangeEnumArray(scg::IEnumerable<global::UnitTest.Issues.TestProtos.DeprecatedEnum> values) {

+        PrepareBuilder();

         result.enumArray_.Add(values);

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder ClearEnumArray() {

+        PrepareBuilder();

         result.enumArray_.Clear();

         return this;

       }

diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestGoogleSizeProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestGoogleSizeProtoFile.cs
index e38fe007..9ba1919e 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestGoogleSizeProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestGoogleSizeProtoFile.cs
@@ -607,7 +607,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(SizeMessage1 prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -617,21 +617,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new SizeMessage1();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(SizeMessage1 cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      SizeMessage1 result;

+      

+      private SizeMessage1 PrepareBuilder() {

+        if (builderIsReadOnly) {

+          SizeMessage1 original = result;

+          result = new SizeMessage1();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      SizeMessage1 result = new SizeMessage1();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override SizeMessage1 MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new SizeMessage1();

+        result = DefaultInstance ?? new SizeMessage1();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -643,13 +670,12 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override SizeMessage1 BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.field5_.MakeReadOnly();

-        SizeMessage1 returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       

@@ -662,11 +688,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField1(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField1 = true;

         result.field1_ = value;

         return this;

       }

       public Builder ClearField1() {

+        PrepareBuilder();

         result.hasField1 = false;

         result.field1_ = "";

         return this;

@@ -681,11 +709,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField9(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField9 = true;

         result.field9_ = value;

         return this;

       }

       public Builder ClearField9() {

+        PrepareBuilder();

         result.hasField9 = false;

         result.field9_ = "";

         return this;

@@ -700,11 +730,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField18(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField18 = true;

         result.field18_ = value;

         return this;

       }

       public Builder ClearField18() {

+        PrepareBuilder();

         result.hasField18 = false;

         result.field18_ = "";

         return this;

@@ -718,11 +750,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField80(value); }

       }

       public Builder SetField80(bool value) {

+        PrepareBuilder();

         result.hasField80 = true;

         result.field80_ = value;

         return this;

       }

       public Builder ClearField80() {

+        PrepareBuilder();

         result.hasField80 = false;

         result.field80_ = false;

         return this;

@@ -736,11 +770,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField81(value); }

       }

       public Builder SetField81(bool value) {

+        PrepareBuilder();

         result.hasField81 = true;

         result.field81_ = value;

         return this;

       }

       public Builder ClearField81() {

+        PrepareBuilder();

         result.hasField81 = false;

         result.field81_ = true;

         return this;

@@ -754,11 +790,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField2(value); }

       }

       public Builder SetField2(int value) {

+        PrepareBuilder();

         result.hasField2 = true;

         result.field2_ = value;

         return this;

       }

       public Builder ClearField2() {

+        PrepareBuilder();

         result.hasField2 = false;

         result.field2_ = 0;

         return this;

@@ -772,11 +810,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField3(value); }

       }

       public Builder SetField3(int value) {

+        PrepareBuilder();

         result.hasField3 = true;

         result.field3_ = value;

         return this;

       }

       public Builder ClearField3() {

+        PrepareBuilder();

         result.hasField3 = false;

         result.field3_ = 0;

         return this;

@@ -790,11 +830,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField280(value); }

       }

       public Builder SetField280(int value) {

+        PrepareBuilder();

         result.hasField280 = true;

         result.field280_ = value;

         return this;

       }

       public Builder ClearField280() {

+        PrepareBuilder();

         result.hasField280 = false;

         result.field280_ = 0;

         return this;

@@ -808,11 +850,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField6(value); }

       }

       public Builder SetField6(int value) {

+        PrepareBuilder();

         result.hasField6 = true;

         result.field6_ = value;

         return this;

       }

       public Builder ClearField6() {

+        PrepareBuilder();

         result.hasField6 = false;

         result.field6_ = 0;

         return this;

@@ -826,11 +870,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField22(value); }

       }

       public Builder SetField22(long value) {

+        PrepareBuilder();

         result.hasField22 = true;

         result.field22_ = value;

         return this;

       }

       public Builder ClearField22() {

+        PrepareBuilder();

         result.hasField22 = false;

         result.field22_ = 0L;

         return this;

@@ -845,11 +891,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField4(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField4 = true;

         result.field4_ = value;

         return this;

       }

       public Builder ClearField4() {

+        PrepareBuilder();

         result.hasField4 = false;

         result.field4_ = "";

         return this;

@@ -857,7 +905,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> Field5List {

-        get { return result.field5_; }

+        get { return PrepareBuilder().field5_; }

       }

       public int Field5Count {

         get { return result.Field5Count; }

@@ -868,20 +916,24 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetField5(int index, ulong value) {

+        PrepareBuilder();

         result.field5_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddField5(ulong value) {

+        PrepareBuilder();

         result.field5_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeField5(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.field5_.Add(values);

         return this;

       }

       public Builder ClearField5() {

+        PrepareBuilder();

         result.field5_.Clear();

         return this;

       }

@@ -894,11 +946,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField59(value); }

       }

       public Builder SetField59(bool value) {

+        PrepareBuilder();

         result.hasField59 = true;

         result.field59_ = value;

         return this;

       }

       public Builder ClearField59() {

+        PrepareBuilder();

         result.hasField59 = false;

         result.field59_ = false;

         return this;

@@ -913,11 +967,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField7(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField7 = true;

         result.field7_ = value;

         return this;

       }

       public Builder ClearField7() {

+        PrepareBuilder();

         result.hasField7 = false;

         result.field7_ = "";

         return this;

@@ -931,11 +987,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField16(value); }

       }

       public Builder SetField16(int value) {

+        PrepareBuilder();

         result.hasField16 = true;

         result.field16_ = value;

         return this;

       }

       public Builder ClearField16() {

+        PrepareBuilder();

         result.hasField16 = false;

         result.field16_ = 0;

         return this;

@@ -949,11 +1007,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField130(value); }

       }

       public Builder SetField130(int value) {

+        PrepareBuilder();

         result.hasField130 = true;

         result.field130_ = value;

         return this;

       }

       public Builder ClearField130() {

+        PrepareBuilder();

         result.hasField130 = false;

         result.field130_ = 0;

         return this;

@@ -967,11 +1027,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField12(value); }

       }

       public Builder SetField12(bool value) {

+        PrepareBuilder();

         result.hasField12 = true;

         result.field12_ = value;

         return this;

       }

       public Builder ClearField12() {

+        PrepareBuilder();

         result.hasField12 = false;

         result.field12_ = true;

         return this;

@@ -985,11 +1047,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField17(value); }

       }

       public Builder SetField17(bool value) {

+        PrepareBuilder();

         result.hasField17 = true;

         result.field17_ = value;

         return this;

       }

       public Builder ClearField17() {

+        PrepareBuilder();

         result.hasField17 = false;

         result.field17_ = true;

         return this;

@@ -1003,11 +1067,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField13(value); }

       }

       public Builder SetField13(bool value) {

+        PrepareBuilder();

         result.hasField13 = true;

         result.field13_ = value;

         return this;

       }

       public Builder ClearField13() {

+        PrepareBuilder();

         result.hasField13 = false;

         result.field13_ = true;

         return this;

@@ -1021,11 +1087,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField14(value); }

       }

       public Builder SetField14(bool value) {

+        PrepareBuilder();

         result.hasField14 = true;

         result.field14_ = value;

         return this;

       }

       public Builder ClearField14() {

+        PrepareBuilder();

         result.hasField14 = false;

         result.field14_ = true;

         return this;

@@ -1039,11 +1107,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField104(value); }

       }

       public Builder SetField104(int value) {

+        PrepareBuilder();

         result.hasField104 = true;

         result.field104_ = value;

         return this;

       }

       public Builder ClearField104() {

+        PrepareBuilder();

         result.hasField104 = false;

         result.field104_ = 0;

         return this;

@@ -1057,11 +1127,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField100(value); }

       }

       public Builder SetField100(int value) {

+        PrepareBuilder();

         result.hasField100 = true;

         result.field100_ = value;

         return this;

       }

       public Builder ClearField100() {

+        PrepareBuilder();

         result.hasField100 = false;

         result.field100_ = 0;

         return this;

@@ -1075,11 +1147,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField101(value); }

       }

       public Builder SetField101(int value) {

+        PrepareBuilder();

         result.hasField101 = true;

         result.field101_ = value;

         return this;

       }

       public Builder ClearField101() {

+        PrepareBuilder();

         result.hasField101 = false;

         result.field101_ = 0;

         return this;

@@ -1094,11 +1168,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField102(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField102 = true;

         result.field102_ = value;

         return this;

       }

       public Builder ClearField102() {

+        PrepareBuilder();

         result.hasField102 = false;

         result.field102_ = "";

         return this;

@@ -1113,11 +1189,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField103(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField103 = true;

         result.field103_ = value;

         return this;

       }

       public Builder ClearField103() {

+        PrepareBuilder();

         result.hasField103 = false;

         result.field103_ = "";

         return this;

@@ -1131,11 +1209,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField29(value); }

       }

       public Builder SetField29(int value) {

+        PrepareBuilder();

         result.hasField29 = true;

         result.field29_ = value;

         return this;

       }

       public Builder ClearField29() {

+        PrepareBuilder();

         result.hasField29 = false;

         result.field29_ = 0;

         return this;

@@ -1149,11 +1229,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField30(value); }

       }

       public Builder SetField30(bool value) {

+        PrepareBuilder();

         result.hasField30 = true;

         result.field30_ = value;

         return this;

       }

       public Builder ClearField30() {

+        PrepareBuilder();

         result.hasField30 = false;

         result.field30_ = false;

         return this;

@@ -1167,11 +1249,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField60(value); }

       }

       public Builder SetField60(int value) {

+        PrepareBuilder();

         result.hasField60 = true;

         result.field60_ = value;

         return this;

       }

       public Builder ClearField60() {

+        PrepareBuilder();

         result.hasField60 = false;

         result.field60_ = -1;

         return this;

@@ -1185,11 +1269,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField271(value); }

       }

       public Builder SetField271(int value) {

+        PrepareBuilder();

         result.hasField271 = true;

         result.field271_ = value;

         return this;

       }

       public Builder ClearField271() {

+        PrepareBuilder();

         result.hasField271 = false;

         result.field271_ = -1;

         return this;

@@ -1203,11 +1289,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField272(value); }

       }

       public Builder SetField272(int value) {

+        PrepareBuilder();

         result.hasField272 = true;

         result.field272_ = value;

         return this;

       }

       public Builder ClearField272() {

+        PrepareBuilder();

         result.hasField272 = false;

         result.field272_ = -1;

         return this;

@@ -1221,11 +1309,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField150(value); }

       }

       public Builder SetField150(int value) {

+        PrepareBuilder();

         result.hasField150 = true;

         result.field150_ = value;

         return this;

       }

       public Builder ClearField150() {

+        PrepareBuilder();

         result.hasField150 = false;

         result.field150_ = 0;

         return this;

@@ -1239,11 +1329,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField23(value); }

       }

       public Builder SetField23(int value) {

+        PrepareBuilder();

         result.hasField23 = true;

         result.field23_ = value;

         return this;

       }

       public Builder ClearField23() {

+        PrepareBuilder();

         result.hasField23 = false;

         result.field23_ = 0;

         return this;

@@ -1257,11 +1349,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField24(value); }

       }

       public Builder SetField24(bool value) {

+        PrepareBuilder();

         result.hasField24 = true;

         result.field24_ = value;

         return this;

       }

       public Builder ClearField24() {

+        PrepareBuilder();

         result.hasField24 = false;

         result.field24_ = false;

         return this;

@@ -1275,11 +1369,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField25(value); }

       }

       public Builder SetField25(int value) {

+        PrepareBuilder();

         result.hasField25 = true;

         result.field25_ = value;

         return this;

       }

       public Builder ClearField25() {

+        PrepareBuilder();

         result.hasField25 = false;

         result.field25_ = 0;

         return this;

@@ -1294,18 +1390,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField15(global::Google.ProtocolBuffers.TestProtos.SizeMessage1SubMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField15 = true;

         result.field15_ = value;

         return this;

       }

       public Builder SetField15(global::Google.ProtocolBuffers.TestProtos.SizeMessage1SubMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasField15 = true;

         result.field15_ = builderForValue.Build();

         return this;

       }

       public Builder MergeField15(global::Google.ProtocolBuffers.TestProtos.SizeMessage1SubMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasField15 &&

             result.field15_ != global::Google.ProtocolBuffers.TestProtos.SizeMessage1SubMessage.DefaultInstance) {

             result.field15_ = global::Google.ProtocolBuffers.TestProtos.SizeMessage1SubMessage.CreateBuilder(result.field15_).MergeFrom(value).BuildPartial();

@@ -1316,6 +1415,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearField15() {

+        PrepareBuilder();

         result.hasField15 = false;

         result.field15_ = global::Google.ProtocolBuffers.TestProtos.SizeMessage1SubMessage.DefaultInstance;

         return this;

@@ -1329,11 +1429,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField78(value); }

       }

       public Builder SetField78(bool value) {

+        PrepareBuilder();

         result.hasField78 = true;

         result.field78_ = value;

         return this;

       }

       public Builder ClearField78() {

+        PrepareBuilder();

         result.hasField78 = false;

         result.field78_ = false;

         return this;

@@ -1347,11 +1449,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField67(value); }

       }

       public Builder SetField67(int value) {

+        PrepareBuilder();

         result.hasField67 = true;

         result.field67_ = value;

         return this;

       }

       public Builder ClearField67() {

+        PrepareBuilder();

         result.hasField67 = false;

         result.field67_ = 0;

         return this;

@@ -1365,11 +1469,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField68(value); }

       }

       public Builder SetField68(int value) {

+        PrepareBuilder();

         result.hasField68 = true;

         result.field68_ = value;

         return this;

       }

       public Builder ClearField68() {

+        PrepareBuilder();

         result.hasField68 = false;

         result.field68_ = 0;

         return this;

@@ -1383,11 +1489,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField128(value); }

       }

       public Builder SetField128(int value) {

+        PrepareBuilder();

         result.hasField128 = true;

         result.field128_ = value;

         return this;

       }

       public Builder ClearField128() {

+        PrepareBuilder();

         result.hasField128 = false;

         result.field128_ = 0;

         return this;

@@ -1402,11 +1510,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField129(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField129 = true;

         result.field129_ = value;

         return this;

       }

       public Builder ClearField129() {

+        PrepareBuilder();

         result.hasField129 = false;

         result.field129_ = "xxxxxxxxxxxxxxxxxxxxx";

         return this;

@@ -1420,11 +1530,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField131(value); }

       }

       public Builder SetField131(int value) {

+        PrepareBuilder();

         result.hasField131 = true;

         result.field131_ = value;

         return this;

       }

       public Builder ClearField131() {

+        PrepareBuilder();

         result.hasField131 = false;

         result.field131_ = 0;

         return this;

@@ -1699,7 +1811,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(SizeMessage1SubMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1709,21 +1821,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new SizeMessage1SubMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(SizeMessage1SubMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      SizeMessage1SubMessage result = new SizeMessage1SubMessage();

+      bool builderIsReadOnly;

+      SizeMessage1SubMessage result;

+      

+      private SizeMessage1SubMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          SizeMessage1SubMessage original = result;

+          result = new SizeMessage1SubMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override SizeMessage1SubMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new SizeMessage1SubMessage();

+        result = DefaultInstance ?? new SizeMessage1SubMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1735,12 +1874,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override SizeMessage1SubMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        SizeMessage1SubMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       

@@ -1752,11 +1890,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField1(value); }

       }

       public Builder SetField1(int value) {

+        PrepareBuilder();

         result.hasField1 = true;

         result.field1_ = value;

         return this;

       }

       public Builder ClearField1() {

+        PrepareBuilder();

         result.hasField1 = false;

         result.field1_ = 0;

         return this;

@@ -1770,11 +1910,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField2(value); }

       }

       public Builder SetField2(int value) {

+        PrepareBuilder();

         result.hasField2 = true;

         result.field2_ = value;

         return this;

       }

       public Builder ClearField2() {

+        PrepareBuilder();

         result.hasField2 = false;

         result.field2_ = 0;

         return this;

@@ -1788,11 +1930,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField3(value); }

       }

       public Builder SetField3(int value) {

+        PrepareBuilder();

         result.hasField3 = true;

         result.field3_ = value;

         return this;

       }

       public Builder ClearField3() {

+        PrepareBuilder();

         result.hasField3 = false;

         result.field3_ = 0;

         return this;

@@ -1807,11 +1951,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField15(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField15 = true;

         result.field15_ = value;

         return this;

       }

       public Builder ClearField15() {

+        PrepareBuilder();

         result.hasField15 = false;

         result.field15_ = "";

         return this;

@@ -1825,11 +1971,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField12(value); }

       }

       public Builder SetField12(bool value) {

+        PrepareBuilder();

         result.hasField12 = true;

         result.field12_ = value;

         return this;

       }

       public Builder ClearField12() {

+        PrepareBuilder();

         result.hasField12 = false;

         result.field12_ = true;

         return this;

@@ -1843,11 +1991,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField13(value); }

       }

       public Builder SetField13(long value) {

+        PrepareBuilder();

         result.hasField13 = true;

         result.field13_ = value;

         return this;

       }

       public Builder ClearField13() {

+        PrepareBuilder();

         result.hasField13 = false;

         result.field13_ = 0L;

         return this;

@@ -1861,11 +2011,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField14(value); }

       }

       public Builder SetField14(long value) {

+        PrepareBuilder();

         result.hasField14 = true;

         result.field14_ = value;

         return this;

       }

       public Builder ClearField14() {

+        PrepareBuilder();

         result.hasField14 = false;

         result.field14_ = 0L;

         return this;

@@ -1879,11 +2031,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField16(value); }

       }

       public Builder SetField16(int value) {

+        PrepareBuilder();

         result.hasField16 = true;

         result.field16_ = value;

         return this;

       }

       public Builder ClearField16() {

+        PrepareBuilder();

         result.hasField16 = false;

         result.field16_ = 0;

         return this;

@@ -1897,11 +2051,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField19(value); }

       }

       public Builder SetField19(int value) {

+        PrepareBuilder();

         result.hasField19 = true;

         result.field19_ = value;

         return this;

       }

       public Builder ClearField19() {

+        PrepareBuilder();

         result.hasField19 = false;

         result.field19_ = 2;

         return this;

@@ -1915,11 +2071,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField20(value); }

       }

       public Builder SetField20(bool value) {

+        PrepareBuilder();

         result.hasField20 = true;

         result.field20_ = value;

         return this;

       }

       public Builder ClearField20() {

+        PrepareBuilder();

         result.hasField20 = false;

         result.field20_ = true;

         return this;

@@ -1933,11 +2091,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField28(value); }

       }

       public Builder SetField28(bool value) {

+        PrepareBuilder();

         result.hasField28 = true;

         result.field28_ = value;

         return this;

       }

       public Builder ClearField28() {

+        PrepareBuilder();

         result.hasField28 = false;

         result.field28_ = true;

         return this;

@@ -1953,11 +2113,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetField21(ulong value) {

+        PrepareBuilder();

         result.hasField21 = true;

         result.field21_ = value;

         return this;

       }

       public Builder ClearField21() {

+        PrepareBuilder();

         result.hasField21 = false;

         result.field21_ = 0;

         return this;

@@ -1971,11 +2133,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField22(value); }

       }

       public Builder SetField22(int value) {

+        PrepareBuilder();

         result.hasField22 = true;

         result.field22_ = value;

         return this;

       }

       public Builder ClearField22() {

+        PrepareBuilder();

         result.hasField22 = false;

         result.field22_ = 0;

         return this;

@@ -1989,11 +2153,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField23(value); }

       }

       public Builder SetField23(bool value) {

+        PrepareBuilder();

         result.hasField23 = true;

         result.field23_ = value;

         return this;

       }

       public Builder ClearField23() {

+        PrepareBuilder();

         result.hasField23 = false;

         result.field23_ = false;

         return this;

@@ -2007,11 +2173,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField206(value); }

       }

       public Builder SetField206(bool value) {

+        PrepareBuilder();

         result.hasField206 = true;

         result.field206_ = value;

         return this;

       }

       public Builder ClearField206() {

+        PrepareBuilder();

         result.hasField206 = false;

         result.field206_ = false;

         return this;

@@ -2027,11 +2195,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetField203(uint value) {

+        PrepareBuilder();

         result.hasField203 = true;

         result.field203_ = value;

         return this;

       }

       public Builder ClearField203() {

+        PrepareBuilder();

         result.hasField203 = false;

         result.field203_ = 0;

         return this;

@@ -2045,11 +2215,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField204(value); }

       }

       public Builder SetField204(int value) {

+        PrepareBuilder();

         result.hasField204 = true;

         result.field204_ = value;

         return this;

       }

       public Builder ClearField204() {

+        PrepareBuilder();

         result.hasField204 = false;

         result.field204_ = 0;

         return this;

@@ -2064,11 +2236,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField205(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField205 = true;

         result.field205_ = value;

         return this;

       }

       public Builder ClearField205() {

+        PrepareBuilder();

         result.hasField205 = false;

         result.field205_ = "";

         return this;

@@ -2084,11 +2258,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetField207(ulong value) {

+        PrepareBuilder();

         result.hasField207 = true;

         result.field207_ = value;

         return this;

       }

       public Builder ClearField207() {

+        PrepareBuilder();

         result.hasField207 = false;

         result.field207_ = 0UL;

         return this;

@@ -2104,11 +2280,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetField300(ulong value) {

+        PrepareBuilder();

         result.hasField300 = true;

         result.field300_ = value;

         return this;

       }

       public Builder ClearField300() {

+        PrepareBuilder();

         result.hasField300 = false;

         result.field300_ = 0UL;

         return this;

@@ -2377,7 +2555,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(Group1 prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -2387,21 +2565,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new Group1();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(Group1 cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          Group1 result;

           

-          Group1 result = new Group1();

+          private Group1 PrepareBuilder() {

+            if (builderIsReadOnly) {

+              Group1 original = result;

+              result = new Group1();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override Group1 MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new Group1();

+            result = DefaultInstance ?? new Group1();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -2413,15 +2618,14 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Group1 BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

             result.field14_.MakeReadOnly();

             result.field22_.MakeReadOnly();

             result.field73_.MakeReadOnly();

-            Group1 returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           

@@ -2433,11 +2637,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetField11(value); }

           }

           public Builder SetField11(float value) {

+            PrepareBuilder();

             result.hasField11 = true;

             result.field11_ = value;

             return this;

           }

           public Builder ClearField11() {

+            PrepareBuilder();

             result.hasField11 = false;

             result.field11_ = 0F;

             return this;

@@ -2451,11 +2657,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetField26(value); }

           }

           public Builder SetField26(float value) {

+            PrepareBuilder();

             result.hasField26 = true;

             result.field26_ = value;

             return this;

           }

           public Builder ClearField26() {

+            PrepareBuilder();

             result.hasField26 = false;

             result.field26_ = 0F;

             return this;

@@ -2470,11 +2678,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField12(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasField12 = true;

             result.field12_ = value;

             return this;

           }

           public Builder ClearField12() {

+            PrepareBuilder();

             result.hasField12 = false;

             result.field12_ = "";

             return this;

@@ -2489,18 +2699,20 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField13(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasField13 = true;

             result.field13_ = value;

             return this;

           }

           public Builder ClearField13() {

+            PrepareBuilder();

             result.hasField13 = false;

             result.field13_ = "";

             return this;

           }

           

           public pbc::IPopsicleList<string> Field14List {

-            get { return result.field14_; }

+            get { return PrepareBuilder().field14_; }

           }

           public int Field14Count {

             get { return result.Field14Count; }

@@ -2510,19 +2722,23 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField14(int index, string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.field14_[index] = value;

             return this;

           }

           public Builder AddField14(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.field14_.Add(value);

             return this;

           }

           public Builder AddRangeField14(scg::IEnumerable<string> values) {

+            PrepareBuilder();

             result.field14_.Add(values);

             return this;

           }

           public Builder ClearField14() {

+            PrepareBuilder();

             result.field14_.Clear();

             return this;

           }

@@ -2537,11 +2753,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           [global::System.CLSCompliant(false)]

           public Builder SetField15(ulong value) {

+            PrepareBuilder();

             result.hasField15 = true;

             result.field15_ = value;

             return this;

           }

           public Builder ClearField15() {

+            PrepareBuilder();

             result.hasField15 = false;

             result.field15_ = 0UL;

             return this;

@@ -2555,11 +2773,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetField5(value); }

           }

           public Builder SetField5(int value) {

+            PrepareBuilder();

             result.hasField5 = true;

             result.field5_ = value;

             return this;

           }

           public Builder ClearField5() {

+            PrepareBuilder();

             result.hasField5 = false;

             result.field5_ = 0;

             return this;

@@ -2574,11 +2794,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField27(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasField27 = true;

             result.field27_ = value;

             return this;

           }

           public Builder ClearField27() {

+            PrepareBuilder();

             result.hasField27 = false;

             result.field27_ = "";

             return this;

@@ -2592,11 +2814,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetField28(value); }

           }

           public Builder SetField28(int value) {

+            PrepareBuilder();

             result.hasField28 = true;

             result.field28_ = value;

             return this;

           }

           public Builder ClearField28() {

+            PrepareBuilder();

             result.hasField28 = false;

             result.field28_ = 0;

             return this;

@@ -2611,11 +2835,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField29(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasField29 = true;

             result.field29_ = value;

             return this;

           }

           public Builder ClearField29() {

+            PrepareBuilder();

             result.hasField29 = false;

             result.field29_ = "";

             return this;

@@ -2630,18 +2856,20 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField16(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasField16 = true;

             result.field16_ = value;

             return this;

           }

           public Builder ClearField16() {

+            PrepareBuilder();

             result.hasField16 = false;

             result.field16_ = "";

             return this;

           }

           

           public pbc::IPopsicleList<string> Field22List {

-            get { return result.field22_; }

+            get { return PrepareBuilder().field22_; }

           }

           public int Field22Count {

             get { return result.Field22Count; }

@@ -2651,25 +2879,29 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField22(int index, string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.field22_[index] = value;

             return this;

           }

           public Builder AddField22(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.field22_.Add(value);

             return this;

           }

           public Builder AddRangeField22(scg::IEnumerable<string> values) {

+            PrepareBuilder();

             result.field22_.Add(values);

             return this;

           }

           public Builder ClearField22() {

+            PrepareBuilder();

             result.field22_.Clear();

             return this;

           }

           

           public pbc::IPopsicleList<int> Field73List {

-            get { return result.field73_; }

+            get { return PrepareBuilder().field73_; }

           }

           public int Field73Count {

             get { return result.Field73Count; }

@@ -2678,18 +2910,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             return result.GetField73(index);

           }

           public Builder SetField73(int index, int value) {

+            PrepareBuilder();

             result.field73_[index] = value;

             return this;

           }

           public Builder AddField73(int value) {

+            PrepareBuilder();

             result.field73_.Add(value);

             return this;

           }

           public Builder AddRangeField73(scg::IEnumerable<int> values) {

+            PrepareBuilder();

             result.field73_.Add(values);

             return this;

           }

           public Builder ClearField73() {

+            PrepareBuilder();

             result.field73_.Clear();

             return this;

           }

@@ -2702,11 +2938,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetField20(value); }

           }

           public Builder SetField20(int value) {

+            PrepareBuilder();

             result.hasField20 = true;

             result.field20_ = value;

             return this;

           }

           public Builder ClearField20() {

+            PrepareBuilder();

             result.hasField20 = false;

             result.field20_ = 0;

             return this;

@@ -2721,11 +2959,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField24(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasField24 = true;

             result.field24_ = value;

             return this;

           }

           public Builder ClearField24() {

+            PrepareBuilder();

             result.hasField24 = false;

             result.field24_ = "";

             return this;

@@ -2740,18 +2980,21 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField31(global::Google.ProtocolBuffers.TestProtos.SizeMessage2GroupedMessage value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasField31 = true;

             result.field31_ = value;

             return this;

           }

           public Builder SetField31(global::Google.ProtocolBuffers.TestProtos.SizeMessage2GroupedMessage.Builder builderForValue) {

             pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+            PrepareBuilder();

             result.hasField31 = true;

             result.field31_ = builderForValue.Build();

             return this;

           }

           public Builder MergeField31(global::Google.ProtocolBuffers.TestProtos.SizeMessage2GroupedMessage value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             if (result.hasField31 &&

                 result.field31_ != global::Google.ProtocolBuffers.TestProtos.SizeMessage2GroupedMessage.DefaultInstance) {

                 result.field31_ = global::Google.ProtocolBuffers.TestProtos.SizeMessage2GroupedMessage.CreateBuilder(result.field31_).MergeFrom(value).BuildPartial();

@@ -2762,6 +3005,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             return this;

           }

           public Builder ClearField31() {

+            PrepareBuilder();

             result.hasField31 = false;

             result.field31_ = global::Google.ProtocolBuffers.TestProtos.SizeMessage2GroupedMessage.DefaultInstance;

             return this;

@@ -3117,7 +3361,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(SizeMessage2 prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -3127,21 +3371,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new SizeMessage2();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(SizeMessage2 cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      SizeMessage2 result = new SizeMessage2();

+      bool builderIsReadOnly;

+      SizeMessage2 result;

+      

+      private SizeMessage2 PrepareBuilder() {

+        if (builderIsReadOnly) {

+          SizeMessage2 original = result;

+          result = new SizeMessage2();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override SizeMessage2 MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new SizeMessage2();

+        result = DefaultInstance ?? new SizeMessage2();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -3153,16 +3424,15 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override SizeMessage2 BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.group1_.MakeReadOnly();

         result.field128_.MakeReadOnly();

         result.field127_.MakeReadOnly();

         result.field130_.MakeReadOnly();

-        SizeMessage2 returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       

@@ -3175,11 +3445,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField1(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField1 = true;

         result.field1_ = value;

         return this;

       }

       public Builder ClearField1() {

+        PrepareBuilder();

         result.hasField1 = false;

         result.field1_ = "";

         return this;

@@ -3193,11 +3465,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField3(value); }

       }

       public Builder SetField3(long value) {

+        PrepareBuilder();

         result.hasField3 = true;

         result.field3_ = value;

         return this;

       }

       public Builder ClearField3() {

+        PrepareBuilder();

         result.hasField3 = false;

         result.field3_ = 0L;

         return this;

@@ -3211,11 +3485,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField4(value); }

       }

       public Builder SetField4(long value) {

+        PrepareBuilder();

         result.hasField4 = true;

         result.field4_ = value;

         return this;

       }

       public Builder ClearField4() {

+        PrepareBuilder();

         result.hasField4 = false;

         result.field4_ = 0L;

         return this;

@@ -3229,11 +3505,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField30(value); }

       }

       public Builder SetField30(long value) {

+        PrepareBuilder();

         result.hasField30 = true;

         result.field30_ = value;

         return this;

       }

       public Builder ClearField30() {

+        PrepareBuilder();

         result.hasField30 = false;

         result.field30_ = 0L;

         return this;

@@ -3247,11 +3525,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField75(value); }

       }

       public Builder SetField75(bool value) {

+        PrepareBuilder();

         result.hasField75 = true;

         result.field75_ = value;

         return this;

       }

       public Builder ClearField75() {

+        PrepareBuilder();

         result.hasField75 = false;

         result.field75_ = false;

         return this;

@@ -3266,11 +3546,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField6(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField6 = true;

         result.field6_ = value;

         return this;

       }

       public Builder ClearField6() {

+        PrepareBuilder();

         result.hasField6 = false;

         result.field6_ = "";

         return this;

@@ -3285,11 +3567,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField2(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField2 = true;

         result.field2_ = value;

         return this;

       }

       public Builder ClearField2() {

+        PrepareBuilder();

         result.hasField2 = false;

         result.field2_ = pb::ByteString.Empty;

         return this;

@@ -3303,11 +3587,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField21(value); }

       }

       public Builder SetField21(int value) {

+        PrepareBuilder();

         result.hasField21 = true;

         result.field21_ = value;

         return this;

       }

       public Builder ClearField21() {

+        PrepareBuilder();

         result.hasField21 = false;

         result.field21_ = 0;

         return this;

@@ -3321,11 +3607,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField71(value); }

       }

       public Builder SetField71(int value) {

+        PrepareBuilder();

         result.hasField71 = true;

         result.field71_ = value;

         return this;

       }

       public Builder ClearField71() {

+        PrepareBuilder();

         result.hasField71 = false;

         result.field71_ = 0;

         return this;

@@ -3339,11 +3627,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField25(value); }

       }

       public Builder SetField25(float value) {

+        PrepareBuilder();

         result.hasField25 = true;

         result.field25_ = value;

         return this;

       }

       public Builder ClearField25() {

+        PrepareBuilder();

         result.hasField25 = false;

         result.field25_ = 0F;

         return this;

@@ -3357,11 +3647,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField109(value); }

       }

       public Builder SetField109(int value) {

+        PrepareBuilder();

         result.hasField109 = true;

         result.field109_ = value;

         return this;

       }

       public Builder ClearField109() {

+        PrepareBuilder();

         result.hasField109 = false;

         result.field109_ = 0;

         return this;

@@ -3375,11 +3667,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField210(value); }

       }

       public Builder SetField210(int value) {

+        PrepareBuilder();

         result.hasField210 = true;

         result.field210_ = value;

         return this;

       }

       public Builder ClearField210() {

+        PrepareBuilder();

         result.hasField210 = false;

         result.field210_ = 0;

         return this;

@@ -3393,11 +3687,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField211(value); }

       }

       public Builder SetField211(int value) {

+        PrepareBuilder();

         result.hasField211 = true;

         result.field211_ = value;

         return this;

       }

       public Builder ClearField211() {

+        PrepareBuilder();

         result.hasField211 = false;

         result.field211_ = 0;

         return this;

@@ -3411,11 +3707,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField212(value); }

       }

       public Builder SetField212(int value) {

+        PrepareBuilder();

         result.hasField212 = true;

         result.field212_ = value;

         return this;

       }

       public Builder ClearField212() {

+        PrepareBuilder();

         result.hasField212 = false;

         result.field212_ = 0;

         return this;

@@ -3429,11 +3727,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField213(value); }

       }

       public Builder SetField213(int value) {

+        PrepareBuilder();

         result.hasField213 = true;

         result.field213_ = value;

         return this;

       }

       public Builder ClearField213() {

+        PrepareBuilder();

         result.hasField213 = false;

         result.field213_ = 0;

         return this;

@@ -3447,11 +3747,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField216(value); }

       }

       public Builder SetField216(int value) {

+        PrepareBuilder();

         result.hasField216 = true;

         result.field216_ = value;

         return this;

       }

       public Builder ClearField216() {

+        PrepareBuilder();

         result.hasField216 = false;

         result.field216_ = 0;

         return this;

@@ -3465,11 +3767,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField217(value); }

       }

       public Builder SetField217(int value) {

+        PrepareBuilder();

         result.hasField217 = true;

         result.field217_ = value;

         return this;

       }

       public Builder ClearField217() {

+        PrepareBuilder();

         result.hasField217 = false;

         result.field217_ = 0;

         return this;

@@ -3483,11 +3787,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField218(value); }

       }

       public Builder SetField218(int value) {

+        PrepareBuilder();

         result.hasField218 = true;

         result.field218_ = value;

         return this;

       }

       public Builder ClearField218() {

+        PrepareBuilder();

         result.hasField218 = false;

         result.field218_ = 0;

         return this;

@@ -3501,11 +3807,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField220(value); }

       }

       public Builder SetField220(int value) {

+        PrepareBuilder();

         result.hasField220 = true;

         result.field220_ = value;

         return this;

       }

       public Builder ClearField220() {

+        PrepareBuilder();

         result.hasField220 = false;

         result.field220_ = 0;

         return this;

@@ -3519,11 +3827,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField221(value); }

       }

       public Builder SetField221(int value) {

+        PrepareBuilder();

         result.hasField221 = true;

         result.field221_ = value;

         return this;

       }

       public Builder ClearField221() {

+        PrepareBuilder();

         result.hasField221 = false;

         result.field221_ = 0;

         return this;

@@ -3537,11 +3847,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField222(value); }

       }

       public Builder SetField222(float value) {

+        PrepareBuilder();

         result.hasField222 = true;

         result.field222_ = value;

         return this;

       }

       public Builder ClearField222() {

+        PrepareBuilder();

         result.hasField222 = false;

         result.field222_ = 0F;

         return this;

@@ -3555,18 +3867,20 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField63(value); }

       }

       public Builder SetField63(int value) {

+        PrepareBuilder();

         result.hasField63 = true;

         result.field63_ = value;

         return this;

       }

       public Builder ClearField63() {

+        PrepareBuilder();

         result.hasField63 = false;

         result.field63_ = 0;

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.SizeMessage2.Types.Group1> Group1List {

-        get { return result.group1_; }

+        get { return PrepareBuilder().group1_; }

       }

       public int Group1Count {

         get { return result.Group1Count; }

@@ -3576,35 +3890,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetGroup1(int index, global::Google.ProtocolBuffers.TestProtos.SizeMessage2.Types.Group1 value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.group1_[index] = value;

         return this;

       }

       public Builder SetGroup1(int index, global::Google.ProtocolBuffers.TestProtos.SizeMessage2.Types.Group1.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.group1_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddGroup1(global::Google.ProtocolBuffers.TestProtos.SizeMessage2.Types.Group1 value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.group1_.Add(value);

         return this;

       }

       public Builder AddGroup1(global::Google.ProtocolBuffers.TestProtos.SizeMessage2.Types.Group1.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.group1_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeGroup1(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.SizeMessage2.Types.Group1> values) {

+        PrepareBuilder();

         result.group1_.Add(values);

         return this;

       }

       public Builder ClearGroup1() {

+        PrepareBuilder();

         result.group1_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> Field128List {

-        get { return result.field128_; }

+        get { return PrepareBuilder().field128_; }

       }

       public int Field128Count {

         get { return result.Field128Count; }

@@ -3614,19 +3934,23 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField128(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.field128_[index] = value;

         return this;

       }

       public Builder AddField128(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.field128_.Add(value);

         return this;

       }

       public Builder AddRangeField128(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.field128_.Add(values);

         return this;

       }

       public Builder ClearField128() {

+        PrepareBuilder();

         result.field128_.Clear();

         return this;

       }

@@ -3639,18 +3963,20 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField131(value); }

       }

       public Builder SetField131(long value) {

+        PrepareBuilder();

         result.hasField131 = true;

         result.field131_ = value;

         return this;

       }

       public Builder ClearField131() {

+        PrepareBuilder();

         result.hasField131 = false;

         result.field131_ = 0L;

         return this;

       }

       

       public pbc::IPopsicleList<string> Field127List {

-        get { return result.field127_; }

+        get { return PrepareBuilder().field127_; }

       }

       public int Field127Count {

         get { return result.Field127Count; }

@@ -3660,19 +3986,23 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField127(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.field127_[index] = value;

         return this;

       }

       public Builder AddField127(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.field127_.Add(value);

         return this;

       }

       public Builder AddRangeField127(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.field127_.Add(values);

         return this;

       }

       public Builder ClearField127() {

+        PrepareBuilder();

         result.field127_.Clear();

         return this;

       }

@@ -3685,18 +4015,20 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField129(value); }

       }

       public Builder SetField129(int value) {

+        PrepareBuilder();

         result.hasField129 = true;

         result.field129_ = value;

         return this;

       }

       public Builder ClearField129() {

+        PrepareBuilder();

         result.hasField129 = false;

         result.field129_ = 0;

         return this;

       }

       

       public pbc::IPopsicleList<long> Field130List {

-        get { return result.field130_; }

+        get { return PrepareBuilder().field130_; }

       }

       public int Field130Count {

         get { return result.Field130Count; }

@@ -3705,18 +4037,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetField130(index);

       }

       public Builder SetField130(int index, long value) {

+        PrepareBuilder();

         result.field130_[index] = value;

         return this;

       }

       public Builder AddField130(long value) {

+        PrepareBuilder();

         result.field130_.Add(value);

         return this;

       }

       public Builder AddRangeField130(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.field130_.Add(values);

         return this;

       }

       public Builder ClearField130() {

+        PrepareBuilder();

         result.field130_.Clear();

         return this;

       }

@@ -3729,11 +4065,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField205(value); }

       }

       public Builder SetField205(bool value) {

+        PrepareBuilder();

         result.hasField205 = true;

         result.field205_ = value;

         return this;

       }

       public Builder ClearField205() {

+        PrepareBuilder();

         result.hasField205 = false;

         result.field205_ = false;

         return this;

@@ -3747,11 +4085,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField206(value); }

       }

       public Builder SetField206(bool value) {

+        PrepareBuilder();

         result.hasField206 = true;

         result.field206_ = value;

         return this;

       }

       public Builder ClearField206() {

+        PrepareBuilder();

         result.hasField206 = false;

         result.field206_ = false;

         return this;

@@ -3932,7 +4272,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(SizeMessage2GroupedMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -3942,21 +4282,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new SizeMessage2GroupedMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(SizeMessage2GroupedMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      SizeMessage2GroupedMessage result = new SizeMessage2GroupedMessage();

+      bool builderIsReadOnly;

+      SizeMessage2GroupedMessage result;

+      

+      private SizeMessage2GroupedMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          SizeMessage2GroupedMessage original = result;

+          result = new SizeMessage2GroupedMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override SizeMessage2GroupedMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new SizeMessage2GroupedMessage();

+        result = DefaultInstance ?? new SizeMessage2GroupedMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -3968,12 +4335,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override SizeMessage2GroupedMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        SizeMessage2GroupedMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       

@@ -3985,11 +4351,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField1(value); }

       }

       public Builder SetField1(float value) {

+        PrepareBuilder();

         result.hasField1 = true;

         result.field1_ = value;

         return this;

       }

       public Builder ClearField1() {

+        PrepareBuilder();

         result.hasField1 = false;

         result.field1_ = 0F;

         return this;

@@ -4003,11 +4371,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField2(value); }

       }

       public Builder SetField2(float value) {

+        PrepareBuilder();

         result.hasField2 = true;

         result.field2_ = value;

         return this;

       }

       public Builder ClearField2() {

+        PrepareBuilder();

         result.hasField2 = false;

         result.field2_ = 0F;

         return this;

@@ -4021,11 +4391,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField3(value); }

       }

       public Builder SetField3(float value) {

+        PrepareBuilder();

         result.hasField3 = true;

         result.field3_ = value;

         return this;

       }

       public Builder ClearField3() {

+        PrepareBuilder();

         result.hasField3 = false;

         result.field3_ = 0F;

         return this;

@@ -4039,11 +4411,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField4(value); }

       }

       public Builder SetField4(bool value) {

+        PrepareBuilder();

         result.hasField4 = true;

         result.field4_ = value;

         return this;

       }

       public Builder ClearField4() {

+        PrepareBuilder();

         result.hasField4 = false;

         result.field4_ = false;

         return this;

@@ -4057,11 +4431,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField5(value); }

       }

       public Builder SetField5(bool value) {

+        PrepareBuilder();

         result.hasField5 = true;

         result.field5_ = value;

         return this;

       }

       public Builder ClearField5() {

+        PrepareBuilder();

         result.hasField5 = false;

         result.field5_ = false;

         return this;

@@ -4075,11 +4451,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField6(value); }

       }

       public Builder SetField6(bool value) {

+        PrepareBuilder();

         result.hasField6 = true;

         result.field6_ = value;

         return this;

       }

       public Builder ClearField6() {

+        PrepareBuilder();

         result.hasField6 = false;

         result.field6_ = true;

         return this;

@@ -4093,11 +4471,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField7(value); }

       }

       public Builder SetField7(bool value) {

+        PrepareBuilder();

         result.hasField7 = true;

         result.field7_ = value;

         return this;

       }

       public Builder ClearField7() {

+        PrepareBuilder();

         result.hasField7 = false;

         result.field7_ = false;

         return this;

@@ -4111,11 +4491,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField8(value); }

       }

       public Builder SetField8(float value) {

+        PrepareBuilder();

         result.hasField8 = true;

         result.field8_ = value;

         return this;

       }

       public Builder ClearField8() {

+        PrepareBuilder();

         result.hasField8 = false;

         result.field8_ = 0F;

         return this;

@@ -4129,11 +4511,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField9(value); }

       }

       public Builder SetField9(bool value) {

+        PrepareBuilder();

         result.hasField9 = true;

         result.field9_ = value;

         return this;

       }

       public Builder ClearField9() {

+        PrepareBuilder();

         result.hasField9 = false;

         result.field9_ = false;

         return this;

@@ -4147,11 +4531,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField10(value); }

       }

       public Builder SetField10(float value) {

+        PrepareBuilder();

         result.hasField10 = true;

         result.field10_ = value;

         return this;

       }

       public Builder ClearField10() {

+        PrepareBuilder();

         result.hasField10 = false;

         result.field10_ = 0F;

         return this;

@@ -4165,11 +4551,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField11(value); }

       }

       public Builder SetField11(long value) {

+        PrepareBuilder();

         result.hasField11 = true;

         result.field11_ = value;

         return this;

       }

       public Builder ClearField11() {

+        PrepareBuilder();

         result.hasField11 = false;

         result.field11_ = 0L;

         return this;

diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestGoogleSpeedProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestGoogleSpeedProtoFile.cs
index 93589ecf..496fb436 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestGoogleSpeedProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestGoogleSpeedProtoFile.cs
@@ -886,7 +886,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(SpeedMessage1 prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -896,21 +896,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new SpeedMessage1();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(SpeedMessage1 cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      SpeedMessage1 result;

       

-      SpeedMessage1 result = new SpeedMessage1();

+      private SpeedMessage1 PrepareBuilder() {

+        if (builderIsReadOnly) {

+          SpeedMessage1 original = result;

+          result = new SpeedMessage1();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override SpeedMessage1 MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new SpeedMessage1();

+        result = DefaultInstance ?? new SpeedMessage1();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -922,13 +949,12 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override SpeedMessage1 BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.field5_.MakeReadOnly();

-        SpeedMessage1 returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -942,6 +968,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(SpeedMessage1 other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.SpeedMessage1.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasField1) {

           Field1 = other.Field1;

         }

@@ -1074,6 +1101,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1296,11 +1324,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField1(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField1 = true;

         result.field1_ = value;

         return this;

       }

       public Builder ClearField1() {

+        PrepareBuilder();

         result.hasField1 = false;

         result.field1_ = "";

         return this;

@@ -1315,11 +1345,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField9(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField9 = true;

         result.field9_ = value;

         return this;

       }

       public Builder ClearField9() {

+        PrepareBuilder();

         result.hasField9 = false;

         result.field9_ = "";

         return this;

@@ -1334,11 +1366,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField18(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField18 = true;

         result.field18_ = value;

         return this;

       }

       public Builder ClearField18() {

+        PrepareBuilder();

         result.hasField18 = false;

         result.field18_ = "";

         return this;

@@ -1352,11 +1386,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField80(value); }

       }

       public Builder SetField80(bool value) {

+        PrepareBuilder();

         result.hasField80 = true;

         result.field80_ = value;

         return this;

       }

       public Builder ClearField80() {

+        PrepareBuilder();

         result.hasField80 = false;

         result.field80_ = false;

         return this;

@@ -1370,11 +1406,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField81(value); }

       }

       public Builder SetField81(bool value) {

+        PrepareBuilder();

         result.hasField81 = true;

         result.field81_ = value;

         return this;

       }

       public Builder ClearField81() {

+        PrepareBuilder();

         result.hasField81 = false;

         result.field81_ = true;

         return this;

@@ -1388,11 +1426,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField2(value); }

       }

       public Builder SetField2(int value) {

+        PrepareBuilder();

         result.hasField2 = true;

         result.field2_ = value;

         return this;

       }

       public Builder ClearField2() {

+        PrepareBuilder();

         result.hasField2 = false;

         result.field2_ = 0;

         return this;

@@ -1406,11 +1446,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField3(value); }

       }

       public Builder SetField3(int value) {

+        PrepareBuilder();

         result.hasField3 = true;

         result.field3_ = value;

         return this;

       }

       public Builder ClearField3() {

+        PrepareBuilder();

         result.hasField3 = false;

         result.field3_ = 0;

         return this;

@@ -1424,11 +1466,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField280(value); }

       }

       public Builder SetField280(int value) {

+        PrepareBuilder();

         result.hasField280 = true;

         result.field280_ = value;

         return this;

       }

       public Builder ClearField280() {

+        PrepareBuilder();

         result.hasField280 = false;

         result.field280_ = 0;

         return this;

@@ -1442,11 +1486,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField6(value); }

       }

       public Builder SetField6(int value) {

+        PrepareBuilder();

         result.hasField6 = true;

         result.field6_ = value;

         return this;

       }

       public Builder ClearField6() {

+        PrepareBuilder();

         result.hasField6 = false;

         result.field6_ = 0;

         return this;

@@ -1460,11 +1506,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField22(value); }

       }

       public Builder SetField22(long value) {

+        PrepareBuilder();

         result.hasField22 = true;

         result.field22_ = value;

         return this;

       }

       public Builder ClearField22() {

+        PrepareBuilder();

         result.hasField22 = false;

         result.field22_ = 0L;

         return this;

@@ -1479,11 +1527,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField4(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField4 = true;

         result.field4_ = value;

         return this;

       }

       public Builder ClearField4() {

+        PrepareBuilder();

         result.hasField4 = false;

         result.field4_ = "";

         return this;

@@ -1491,7 +1541,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> Field5List {

-        get { return result.field5_; }

+        get { return PrepareBuilder().field5_; }

       }

       public int Field5Count {

         get { return result.Field5Count; }

@@ -1502,20 +1552,24 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetField5(int index, ulong value) {

+        PrepareBuilder();

         result.field5_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddField5(ulong value) {

+        PrepareBuilder();

         result.field5_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeField5(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.field5_.Add(values);

         return this;

       }

       public Builder ClearField5() {

+        PrepareBuilder();

         result.field5_.Clear();

         return this;

       }

@@ -1528,11 +1582,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField59(value); }

       }

       public Builder SetField59(bool value) {

+        PrepareBuilder();

         result.hasField59 = true;

         result.field59_ = value;

         return this;

       }

       public Builder ClearField59() {

+        PrepareBuilder();

         result.hasField59 = false;

         result.field59_ = false;

         return this;

@@ -1547,11 +1603,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField7(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField7 = true;

         result.field7_ = value;

         return this;

       }

       public Builder ClearField7() {

+        PrepareBuilder();

         result.hasField7 = false;

         result.field7_ = "";

         return this;

@@ -1565,11 +1623,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField16(value); }

       }

       public Builder SetField16(int value) {

+        PrepareBuilder();

         result.hasField16 = true;

         result.field16_ = value;

         return this;

       }

       public Builder ClearField16() {

+        PrepareBuilder();

         result.hasField16 = false;

         result.field16_ = 0;

         return this;

@@ -1583,11 +1643,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField130(value); }

       }

       public Builder SetField130(int value) {

+        PrepareBuilder();

         result.hasField130 = true;

         result.field130_ = value;

         return this;

       }

       public Builder ClearField130() {

+        PrepareBuilder();

         result.hasField130 = false;

         result.field130_ = 0;

         return this;

@@ -1601,11 +1663,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField12(value); }

       }

       public Builder SetField12(bool value) {

+        PrepareBuilder();

         result.hasField12 = true;

         result.field12_ = value;

         return this;

       }

       public Builder ClearField12() {

+        PrepareBuilder();

         result.hasField12 = false;

         result.field12_ = true;

         return this;

@@ -1619,11 +1683,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField17(value); }

       }

       public Builder SetField17(bool value) {

+        PrepareBuilder();

         result.hasField17 = true;

         result.field17_ = value;

         return this;

       }

       public Builder ClearField17() {

+        PrepareBuilder();

         result.hasField17 = false;

         result.field17_ = true;

         return this;

@@ -1637,11 +1703,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField13(value); }

       }

       public Builder SetField13(bool value) {

+        PrepareBuilder();

         result.hasField13 = true;

         result.field13_ = value;

         return this;

       }

       public Builder ClearField13() {

+        PrepareBuilder();

         result.hasField13 = false;

         result.field13_ = true;

         return this;

@@ -1655,11 +1723,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField14(value); }

       }

       public Builder SetField14(bool value) {

+        PrepareBuilder();

         result.hasField14 = true;

         result.field14_ = value;

         return this;

       }

       public Builder ClearField14() {

+        PrepareBuilder();

         result.hasField14 = false;

         result.field14_ = true;

         return this;

@@ -1673,11 +1743,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField104(value); }

       }

       public Builder SetField104(int value) {

+        PrepareBuilder();

         result.hasField104 = true;

         result.field104_ = value;

         return this;

       }

       public Builder ClearField104() {

+        PrepareBuilder();

         result.hasField104 = false;

         result.field104_ = 0;

         return this;

@@ -1691,11 +1763,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField100(value); }

       }

       public Builder SetField100(int value) {

+        PrepareBuilder();

         result.hasField100 = true;

         result.field100_ = value;

         return this;

       }

       public Builder ClearField100() {

+        PrepareBuilder();

         result.hasField100 = false;

         result.field100_ = 0;

         return this;

@@ -1709,11 +1783,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField101(value); }

       }

       public Builder SetField101(int value) {

+        PrepareBuilder();

         result.hasField101 = true;

         result.field101_ = value;

         return this;

       }

       public Builder ClearField101() {

+        PrepareBuilder();

         result.hasField101 = false;

         result.field101_ = 0;

         return this;

@@ -1728,11 +1804,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField102(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField102 = true;

         result.field102_ = value;

         return this;

       }

       public Builder ClearField102() {

+        PrepareBuilder();

         result.hasField102 = false;

         result.field102_ = "";

         return this;

@@ -1747,11 +1825,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField103(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField103 = true;

         result.field103_ = value;

         return this;

       }

       public Builder ClearField103() {

+        PrepareBuilder();

         result.hasField103 = false;

         result.field103_ = "";

         return this;

@@ -1765,11 +1845,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField29(value); }

       }

       public Builder SetField29(int value) {

+        PrepareBuilder();

         result.hasField29 = true;

         result.field29_ = value;

         return this;

       }

       public Builder ClearField29() {

+        PrepareBuilder();

         result.hasField29 = false;

         result.field29_ = 0;

         return this;

@@ -1783,11 +1865,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField30(value); }

       }

       public Builder SetField30(bool value) {

+        PrepareBuilder();

         result.hasField30 = true;

         result.field30_ = value;

         return this;

       }

       public Builder ClearField30() {

+        PrepareBuilder();

         result.hasField30 = false;

         result.field30_ = false;

         return this;

@@ -1801,11 +1885,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField60(value); }

       }

       public Builder SetField60(int value) {

+        PrepareBuilder();

         result.hasField60 = true;

         result.field60_ = value;

         return this;

       }

       public Builder ClearField60() {

+        PrepareBuilder();

         result.hasField60 = false;

         result.field60_ = -1;

         return this;

@@ -1819,11 +1905,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField271(value); }

       }

       public Builder SetField271(int value) {

+        PrepareBuilder();

         result.hasField271 = true;

         result.field271_ = value;

         return this;

       }

       public Builder ClearField271() {

+        PrepareBuilder();

         result.hasField271 = false;

         result.field271_ = -1;

         return this;

@@ -1837,11 +1925,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField272(value); }

       }

       public Builder SetField272(int value) {

+        PrepareBuilder();

         result.hasField272 = true;

         result.field272_ = value;

         return this;

       }

       public Builder ClearField272() {

+        PrepareBuilder();

         result.hasField272 = false;

         result.field272_ = -1;

         return this;

@@ -1855,11 +1945,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField150(value); }

       }

       public Builder SetField150(int value) {

+        PrepareBuilder();

         result.hasField150 = true;

         result.field150_ = value;

         return this;

       }

       public Builder ClearField150() {

+        PrepareBuilder();

         result.hasField150 = false;

         result.field150_ = 0;

         return this;

@@ -1873,11 +1965,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField23(value); }

       }

       public Builder SetField23(int value) {

+        PrepareBuilder();

         result.hasField23 = true;

         result.field23_ = value;

         return this;

       }

       public Builder ClearField23() {

+        PrepareBuilder();

         result.hasField23 = false;

         result.field23_ = 0;

         return this;

@@ -1891,11 +1985,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField24(value); }

       }

       public Builder SetField24(bool value) {

+        PrepareBuilder();

         result.hasField24 = true;

         result.field24_ = value;

         return this;

       }

       public Builder ClearField24() {

+        PrepareBuilder();

         result.hasField24 = false;

         result.field24_ = false;

         return this;

@@ -1909,11 +2005,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField25(value); }

       }

       public Builder SetField25(int value) {

+        PrepareBuilder();

         result.hasField25 = true;

         result.field25_ = value;

         return this;

       }

       public Builder ClearField25() {

+        PrepareBuilder();

         result.hasField25 = false;

         result.field25_ = 0;

         return this;

@@ -1928,18 +2026,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField15(global::Google.ProtocolBuffers.TestProtos.SpeedMessage1SubMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField15 = true;

         result.field15_ = value;

         return this;

       }

       public Builder SetField15(global::Google.ProtocolBuffers.TestProtos.SpeedMessage1SubMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasField15 = true;

         result.field15_ = builderForValue.Build();

         return this;

       }

       public Builder MergeField15(global::Google.ProtocolBuffers.TestProtos.SpeedMessage1SubMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasField15 &&

             result.field15_ != global::Google.ProtocolBuffers.TestProtos.SpeedMessage1SubMessage.DefaultInstance) {

             result.field15_ = global::Google.ProtocolBuffers.TestProtos.SpeedMessage1SubMessage.CreateBuilder(result.field15_).MergeFrom(value).BuildPartial();

@@ -1950,6 +2051,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearField15() {

+        PrepareBuilder();

         result.hasField15 = false;

         result.field15_ = global::Google.ProtocolBuffers.TestProtos.SpeedMessage1SubMessage.DefaultInstance;

         return this;

@@ -1963,11 +2065,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField78(value); }

       }

       public Builder SetField78(bool value) {

+        PrepareBuilder();

         result.hasField78 = true;

         result.field78_ = value;

         return this;

       }

       public Builder ClearField78() {

+        PrepareBuilder();

         result.hasField78 = false;

         result.field78_ = false;

         return this;

@@ -1981,11 +2085,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField67(value); }

       }

       public Builder SetField67(int value) {

+        PrepareBuilder();

         result.hasField67 = true;

         result.field67_ = value;

         return this;

       }

       public Builder ClearField67() {

+        PrepareBuilder();

         result.hasField67 = false;

         result.field67_ = 0;

         return this;

@@ -1999,11 +2105,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField68(value); }

       }

       public Builder SetField68(int value) {

+        PrepareBuilder();

         result.hasField68 = true;

         result.field68_ = value;

         return this;

       }

       public Builder ClearField68() {

+        PrepareBuilder();

         result.hasField68 = false;

         result.field68_ = 0;

         return this;

@@ -2017,11 +2125,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField128(value); }

       }

       public Builder SetField128(int value) {

+        PrepareBuilder();

         result.hasField128 = true;

         result.field128_ = value;

         return this;

       }

       public Builder ClearField128() {

+        PrepareBuilder();

         result.hasField128 = false;

         result.field128_ = 0;

         return this;

@@ -2036,11 +2146,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField129(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField129 = true;

         result.field129_ = value;

         return this;

       }

       public Builder ClearField129() {

+        PrepareBuilder();

         result.hasField129 = false;

         result.field129_ = "xxxxxxxxxxxxxxxxxxxxx";

         return this;

@@ -2054,11 +2166,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField131(value); }

       }

       public Builder SetField131(int value) {

+        PrepareBuilder();

         result.hasField131 = true;

         result.field131_ = value;

         return this;

       }

       public Builder ClearField131() {

+        PrepareBuilder();

         result.hasField131 = false;

         result.field131_ = 0;

         return this;

@@ -2480,7 +2594,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(SpeedMessage1SubMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -2490,21 +2604,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new SpeedMessage1SubMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(SpeedMessage1SubMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      SpeedMessage1SubMessage result = new SpeedMessage1SubMessage();

+      bool builderIsReadOnly;

+      SpeedMessage1SubMessage result;

+      

+      private SpeedMessage1SubMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          SpeedMessage1SubMessage original = result;

+          result = new SpeedMessage1SubMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override SpeedMessage1SubMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new SpeedMessage1SubMessage();

+        result = DefaultInstance ?? new SpeedMessage1SubMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -2516,12 +2657,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override SpeedMessage1SubMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        SpeedMessage1SubMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -2535,6 +2675,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(SpeedMessage1SubMessage other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.SpeedMessage1SubMessage.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasField1) {

           Field1 = other.Field1;

         }

@@ -2604,6 +2745,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -2735,11 +2877,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField1(value); }

       }

       public Builder SetField1(int value) {

+        PrepareBuilder();

         result.hasField1 = true;

         result.field1_ = value;

         return this;

       }

       public Builder ClearField1() {

+        PrepareBuilder();

         result.hasField1 = false;

         result.field1_ = 0;

         return this;

@@ -2753,11 +2897,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField2(value); }

       }

       public Builder SetField2(int value) {

+        PrepareBuilder();

         result.hasField2 = true;

         result.field2_ = value;

         return this;

       }

       public Builder ClearField2() {

+        PrepareBuilder();

         result.hasField2 = false;

         result.field2_ = 0;

         return this;

@@ -2771,11 +2917,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField3(value); }

       }

       public Builder SetField3(int value) {

+        PrepareBuilder();

         result.hasField3 = true;

         result.field3_ = value;

         return this;

       }

       public Builder ClearField3() {

+        PrepareBuilder();

         result.hasField3 = false;

         result.field3_ = 0;

         return this;

@@ -2790,11 +2938,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField15(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField15 = true;

         result.field15_ = value;

         return this;

       }

       public Builder ClearField15() {

+        PrepareBuilder();

         result.hasField15 = false;

         result.field15_ = "";

         return this;

@@ -2808,11 +2958,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField12(value); }

       }

       public Builder SetField12(bool value) {

+        PrepareBuilder();

         result.hasField12 = true;

         result.field12_ = value;

         return this;

       }

       public Builder ClearField12() {

+        PrepareBuilder();

         result.hasField12 = false;

         result.field12_ = true;

         return this;

@@ -2826,11 +2978,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField13(value); }

       }

       public Builder SetField13(long value) {

+        PrepareBuilder();

         result.hasField13 = true;

         result.field13_ = value;

         return this;

       }

       public Builder ClearField13() {

+        PrepareBuilder();

         result.hasField13 = false;

         result.field13_ = 0L;

         return this;

@@ -2844,11 +2998,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField14(value); }

       }

       public Builder SetField14(long value) {

+        PrepareBuilder();

         result.hasField14 = true;

         result.field14_ = value;

         return this;

       }

       public Builder ClearField14() {

+        PrepareBuilder();

         result.hasField14 = false;

         result.field14_ = 0L;

         return this;

@@ -2862,11 +3018,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField16(value); }

       }

       public Builder SetField16(int value) {

+        PrepareBuilder();

         result.hasField16 = true;

         result.field16_ = value;

         return this;

       }

       public Builder ClearField16() {

+        PrepareBuilder();

         result.hasField16 = false;

         result.field16_ = 0;

         return this;

@@ -2880,11 +3038,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField19(value); }

       }

       public Builder SetField19(int value) {

+        PrepareBuilder();

         result.hasField19 = true;

         result.field19_ = value;

         return this;

       }

       public Builder ClearField19() {

+        PrepareBuilder();

         result.hasField19 = false;

         result.field19_ = 2;

         return this;

@@ -2898,11 +3058,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField20(value); }

       }

       public Builder SetField20(bool value) {

+        PrepareBuilder();

         result.hasField20 = true;

         result.field20_ = value;

         return this;

       }

       public Builder ClearField20() {

+        PrepareBuilder();

         result.hasField20 = false;

         result.field20_ = true;

         return this;

@@ -2916,11 +3078,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField28(value); }

       }

       public Builder SetField28(bool value) {

+        PrepareBuilder();

         result.hasField28 = true;

         result.field28_ = value;

         return this;

       }

       public Builder ClearField28() {

+        PrepareBuilder();

         result.hasField28 = false;

         result.field28_ = true;

         return this;

@@ -2936,11 +3100,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetField21(ulong value) {

+        PrepareBuilder();

         result.hasField21 = true;

         result.field21_ = value;

         return this;

       }

       public Builder ClearField21() {

+        PrepareBuilder();

         result.hasField21 = false;

         result.field21_ = 0;

         return this;

@@ -2954,11 +3120,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField22(value); }

       }

       public Builder SetField22(int value) {

+        PrepareBuilder();

         result.hasField22 = true;

         result.field22_ = value;

         return this;

       }

       public Builder ClearField22() {

+        PrepareBuilder();

         result.hasField22 = false;

         result.field22_ = 0;

         return this;

@@ -2972,11 +3140,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField23(value); }

       }

       public Builder SetField23(bool value) {

+        PrepareBuilder();

         result.hasField23 = true;

         result.field23_ = value;

         return this;

       }

       public Builder ClearField23() {

+        PrepareBuilder();

         result.hasField23 = false;

         result.field23_ = false;

         return this;

@@ -2990,11 +3160,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField206(value); }

       }

       public Builder SetField206(bool value) {

+        PrepareBuilder();

         result.hasField206 = true;

         result.field206_ = value;

         return this;

       }

       public Builder ClearField206() {

+        PrepareBuilder();

         result.hasField206 = false;

         result.field206_ = false;

         return this;

@@ -3010,11 +3182,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetField203(uint value) {

+        PrepareBuilder();

         result.hasField203 = true;

         result.field203_ = value;

         return this;

       }

       public Builder ClearField203() {

+        PrepareBuilder();

         result.hasField203 = false;

         result.field203_ = 0;

         return this;

@@ -3028,11 +3202,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField204(value); }

       }

       public Builder SetField204(int value) {

+        PrepareBuilder();

         result.hasField204 = true;

         result.field204_ = value;

         return this;

       }

       public Builder ClearField204() {

+        PrepareBuilder();

         result.hasField204 = false;

         result.field204_ = 0;

         return this;

@@ -3047,11 +3223,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField205(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField205 = true;

         result.field205_ = value;

         return this;

       }

       public Builder ClearField205() {

+        PrepareBuilder();

         result.hasField205 = false;

         result.field205_ = "";

         return this;

@@ -3067,11 +3245,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetField207(ulong value) {

+        PrepareBuilder();

         result.hasField207 = true;

         result.field207_ = value;

         return this;

       }

       public Builder ClearField207() {

+        PrepareBuilder();

         result.hasField207 = false;

         result.field207_ = 0UL;

         return this;

@@ -3087,11 +3267,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetField300(ulong value) {

+        PrepareBuilder();

         result.hasField300 = true;

         result.field300_ = value;

         return this;

       }

       public Builder ClearField300() {

+        PrepareBuilder();

         result.hasField300 = false;

         result.field300_ = 0UL;

         return this;

@@ -3502,7 +3684,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(Group1 prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -3512,21 +3694,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new Group1();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(Group1 cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          Group1 result;

+          

+          private Group1 PrepareBuilder() {

+            if (builderIsReadOnly) {

+              Group1 original = result;

+              result = new Group1();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

           

-          Group1 result = new Group1();

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override Group1 MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new Group1();

+            result = DefaultInstance ?? new Group1();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -3538,15 +3747,14 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Group1 BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

             result.field14_.MakeReadOnly();

             result.field22_.MakeReadOnly();

             result.field73_.MakeReadOnly();

-            Group1 returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -3560,6 +3768,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(Group1 other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.SpeedMessage2.Types.Group1.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasField11) {

               Field11 = other.Field11;

             }

@@ -3617,6 +3826,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -3738,11 +3948,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetField11(value); }

           }

           public Builder SetField11(float value) {

+            PrepareBuilder();

             result.hasField11 = true;

             result.field11_ = value;

             return this;

           }

           public Builder ClearField11() {

+            PrepareBuilder();

             result.hasField11 = false;

             result.field11_ = 0F;

             return this;

@@ -3756,11 +3968,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetField26(value); }

           }

           public Builder SetField26(float value) {

+            PrepareBuilder();

             result.hasField26 = true;

             result.field26_ = value;

             return this;

           }

           public Builder ClearField26() {

+            PrepareBuilder();

             result.hasField26 = false;

             result.field26_ = 0F;

             return this;

@@ -3775,11 +3989,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField12(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasField12 = true;

             result.field12_ = value;

             return this;

           }

           public Builder ClearField12() {

+            PrepareBuilder();

             result.hasField12 = false;

             result.field12_ = "";

             return this;

@@ -3794,18 +4010,20 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField13(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasField13 = true;

             result.field13_ = value;

             return this;

           }

           public Builder ClearField13() {

+            PrepareBuilder();

             result.hasField13 = false;

             result.field13_ = "";

             return this;

           }

           

           public pbc::IPopsicleList<string> Field14List {

-            get { return result.field14_; }

+            get { return PrepareBuilder().field14_; }

           }

           public int Field14Count {

             get { return result.Field14Count; }

@@ -3815,19 +4033,23 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField14(int index, string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.field14_[index] = value;

             return this;

           }

           public Builder AddField14(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.field14_.Add(value);

             return this;

           }

           public Builder AddRangeField14(scg::IEnumerable<string> values) {

+            PrepareBuilder();

             result.field14_.Add(values);

             return this;

           }

           public Builder ClearField14() {

+            PrepareBuilder();

             result.field14_.Clear();

             return this;

           }

@@ -3842,11 +4064,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           [global::System.CLSCompliant(false)]

           public Builder SetField15(ulong value) {

+            PrepareBuilder();

             result.hasField15 = true;

             result.field15_ = value;

             return this;

           }

           public Builder ClearField15() {

+            PrepareBuilder();

             result.hasField15 = false;

             result.field15_ = 0UL;

             return this;

@@ -3860,11 +4084,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetField5(value); }

           }

           public Builder SetField5(int value) {

+            PrepareBuilder();

             result.hasField5 = true;

             result.field5_ = value;

             return this;

           }

           public Builder ClearField5() {

+            PrepareBuilder();

             result.hasField5 = false;

             result.field5_ = 0;

             return this;

@@ -3879,11 +4105,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField27(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasField27 = true;

             result.field27_ = value;

             return this;

           }

           public Builder ClearField27() {

+            PrepareBuilder();

             result.hasField27 = false;

             result.field27_ = "";

             return this;

@@ -3897,11 +4125,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetField28(value); }

           }

           public Builder SetField28(int value) {

+            PrepareBuilder();

             result.hasField28 = true;

             result.field28_ = value;

             return this;

           }

           public Builder ClearField28() {

+            PrepareBuilder();

             result.hasField28 = false;

             result.field28_ = 0;

             return this;

@@ -3916,11 +4146,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField29(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasField29 = true;

             result.field29_ = value;

             return this;

           }

           public Builder ClearField29() {

+            PrepareBuilder();

             result.hasField29 = false;

             result.field29_ = "";

             return this;

@@ -3935,18 +4167,20 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField16(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasField16 = true;

             result.field16_ = value;

             return this;

           }

           public Builder ClearField16() {

+            PrepareBuilder();

             result.hasField16 = false;

             result.field16_ = "";

             return this;

           }

           

           public pbc::IPopsicleList<string> Field22List {

-            get { return result.field22_; }

+            get { return PrepareBuilder().field22_; }

           }

           public int Field22Count {

             get { return result.Field22Count; }

@@ -3956,25 +4190,29 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField22(int index, string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.field22_[index] = value;

             return this;

           }

           public Builder AddField22(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.field22_.Add(value);

             return this;

           }

           public Builder AddRangeField22(scg::IEnumerable<string> values) {

+            PrepareBuilder();

             result.field22_.Add(values);

             return this;

           }

           public Builder ClearField22() {

+            PrepareBuilder();

             result.field22_.Clear();

             return this;

           }

           

           public pbc::IPopsicleList<int> Field73List {

-            get { return result.field73_; }

+            get { return PrepareBuilder().field73_; }

           }

           public int Field73Count {

             get { return result.Field73Count; }

@@ -3983,18 +4221,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             return result.GetField73(index);

           }

           public Builder SetField73(int index, int value) {

+            PrepareBuilder();

             result.field73_[index] = value;

             return this;

           }

           public Builder AddField73(int value) {

+            PrepareBuilder();

             result.field73_.Add(value);

             return this;

           }

           public Builder AddRangeField73(scg::IEnumerable<int> values) {

+            PrepareBuilder();

             result.field73_.Add(values);

             return this;

           }

           public Builder ClearField73() {

+            PrepareBuilder();

             result.field73_.Clear();

             return this;

           }

@@ -4007,11 +4249,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetField20(value); }

           }

           public Builder SetField20(int value) {

+            PrepareBuilder();

             result.hasField20 = true;

             result.field20_ = value;

             return this;

           }

           public Builder ClearField20() {

+            PrepareBuilder();

             result.hasField20 = false;

             result.field20_ = 0;

             return this;

@@ -4026,11 +4270,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField24(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasField24 = true;

             result.field24_ = value;

             return this;

           }

           public Builder ClearField24() {

+            PrepareBuilder();

             result.hasField24 = false;

             result.field24_ = "";

             return this;

@@ -4045,18 +4291,21 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetField31(global::Google.ProtocolBuffers.TestProtos.SpeedMessage2GroupedMessage value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasField31 = true;

             result.field31_ = value;

             return this;

           }

           public Builder SetField31(global::Google.ProtocolBuffers.TestProtos.SpeedMessage2GroupedMessage.Builder builderForValue) {

             pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+            PrepareBuilder();

             result.hasField31 = true;

             result.field31_ = builderForValue.Build();

             return this;

           }

           public Builder MergeField31(global::Google.ProtocolBuffers.TestProtos.SpeedMessage2GroupedMessage value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             if (result.hasField31 &&

                 result.field31_ != global::Google.ProtocolBuffers.TestProtos.SpeedMessage2GroupedMessage.DefaultInstance) {

                 result.field31_ = global::Google.ProtocolBuffers.TestProtos.SpeedMessage2GroupedMessage.CreateBuilder(result.field31_).MergeFrom(value).BuildPartial();

@@ -4067,6 +4316,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             return this;

           }

           public Builder ClearField31() {

+            PrepareBuilder();

             result.hasField31 = false;

             result.field31_ = global::Google.ProtocolBuffers.TestProtos.SpeedMessage2GroupedMessage.DefaultInstance;

             return this;

@@ -4642,7 +4892,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(SpeedMessage2 prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -4652,21 +4902,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new SpeedMessage2();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(SpeedMessage2 cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      SpeedMessage2 result = new SpeedMessage2();

+      bool builderIsReadOnly;

+      SpeedMessage2 result;

+      

+      private SpeedMessage2 PrepareBuilder() {

+        if (builderIsReadOnly) {

+          SpeedMessage2 original = result;

+          result = new SpeedMessage2();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override SpeedMessage2 MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new SpeedMessage2();

+        result = DefaultInstance ?? new SpeedMessage2();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -4678,16 +4955,15 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override SpeedMessage2 BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.group1_.MakeReadOnly();

         result.field128_.MakeReadOnly();

         result.field127_.MakeReadOnly();

         result.field130_.MakeReadOnly();

-        SpeedMessage2 returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -4701,6 +4977,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(SpeedMessage2 other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.SpeedMessage2.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasField1) {

           Field1 = other.Field1;

         }

@@ -4800,6 +5077,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -4973,11 +5251,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField1(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField1 = true;

         result.field1_ = value;

         return this;

       }

       public Builder ClearField1() {

+        PrepareBuilder();

         result.hasField1 = false;

         result.field1_ = "";

         return this;

@@ -4991,11 +5271,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField3(value); }

       }

       public Builder SetField3(long value) {

+        PrepareBuilder();

         result.hasField3 = true;

         result.field3_ = value;

         return this;

       }

       public Builder ClearField3() {

+        PrepareBuilder();

         result.hasField3 = false;

         result.field3_ = 0L;

         return this;

@@ -5009,11 +5291,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField4(value); }

       }

       public Builder SetField4(long value) {

+        PrepareBuilder();

         result.hasField4 = true;

         result.field4_ = value;

         return this;

       }

       public Builder ClearField4() {

+        PrepareBuilder();

         result.hasField4 = false;

         result.field4_ = 0L;

         return this;

@@ -5027,11 +5311,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField30(value); }

       }

       public Builder SetField30(long value) {

+        PrepareBuilder();

         result.hasField30 = true;

         result.field30_ = value;

         return this;

       }

       public Builder ClearField30() {

+        PrepareBuilder();

         result.hasField30 = false;

         result.field30_ = 0L;

         return this;

@@ -5045,11 +5331,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField75(value); }

       }

       public Builder SetField75(bool value) {

+        PrepareBuilder();

         result.hasField75 = true;

         result.field75_ = value;

         return this;

       }

       public Builder ClearField75() {

+        PrepareBuilder();

         result.hasField75 = false;

         result.field75_ = false;

         return this;

@@ -5064,11 +5352,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField6(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField6 = true;

         result.field6_ = value;

         return this;

       }

       public Builder ClearField6() {

+        PrepareBuilder();

         result.hasField6 = false;

         result.field6_ = "";

         return this;

@@ -5083,11 +5373,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField2(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasField2 = true;

         result.field2_ = value;

         return this;

       }

       public Builder ClearField2() {

+        PrepareBuilder();

         result.hasField2 = false;

         result.field2_ = pb::ByteString.Empty;

         return this;

@@ -5101,11 +5393,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField21(value); }

       }

       public Builder SetField21(int value) {

+        PrepareBuilder();

         result.hasField21 = true;

         result.field21_ = value;

         return this;

       }

       public Builder ClearField21() {

+        PrepareBuilder();

         result.hasField21 = false;

         result.field21_ = 0;

         return this;

@@ -5119,11 +5413,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField71(value); }

       }

       public Builder SetField71(int value) {

+        PrepareBuilder();

         result.hasField71 = true;

         result.field71_ = value;

         return this;

       }

       public Builder ClearField71() {

+        PrepareBuilder();

         result.hasField71 = false;

         result.field71_ = 0;

         return this;

@@ -5137,11 +5433,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField25(value); }

       }

       public Builder SetField25(float value) {

+        PrepareBuilder();

         result.hasField25 = true;

         result.field25_ = value;

         return this;

       }

       public Builder ClearField25() {

+        PrepareBuilder();

         result.hasField25 = false;

         result.field25_ = 0F;

         return this;

@@ -5155,11 +5453,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField109(value); }

       }

       public Builder SetField109(int value) {

+        PrepareBuilder();

         result.hasField109 = true;

         result.field109_ = value;

         return this;

       }

       public Builder ClearField109() {

+        PrepareBuilder();

         result.hasField109 = false;

         result.field109_ = 0;

         return this;

@@ -5173,11 +5473,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField210(value); }

       }

       public Builder SetField210(int value) {

+        PrepareBuilder();

         result.hasField210 = true;

         result.field210_ = value;

         return this;

       }

       public Builder ClearField210() {

+        PrepareBuilder();

         result.hasField210 = false;

         result.field210_ = 0;

         return this;

@@ -5191,11 +5493,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField211(value); }

       }

       public Builder SetField211(int value) {

+        PrepareBuilder();

         result.hasField211 = true;

         result.field211_ = value;

         return this;

       }

       public Builder ClearField211() {

+        PrepareBuilder();

         result.hasField211 = false;

         result.field211_ = 0;

         return this;

@@ -5209,11 +5513,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField212(value); }

       }

       public Builder SetField212(int value) {

+        PrepareBuilder();

         result.hasField212 = true;

         result.field212_ = value;

         return this;

       }

       public Builder ClearField212() {

+        PrepareBuilder();

         result.hasField212 = false;

         result.field212_ = 0;

         return this;

@@ -5227,11 +5533,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField213(value); }

       }

       public Builder SetField213(int value) {

+        PrepareBuilder();

         result.hasField213 = true;

         result.field213_ = value;

         return this;

       }

       public Builder ClearField213() {

+        PrepareBuilder();

         result.hasField213 = false;

         result.field213_ = 0;

         return this;

@@ -5245,11 +5553,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField216(value); }

       }

       public Builder SetField216(int value) {

+        PrepareBuilder();

         result.hasField216 = true;

         result.field216_ = value;

         return this;

       }

       public Builder ClearField216() {

+        PrepareBuilder();

         result.hasField216 = false;

         result.field216_ = 0;

         return this;

@@ -5263,11 +5573,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField217(value); }

       }

       public Builder SetField217(int value) {

+        PrepareBuilder();

         result.hasField217 = true;

         result.field217_ = value;

         return this;

       }

       public Builder ClearField217() {

+        PrepareBuilder();

         result.hasField217 = false;

         result.field217_ = 0;

         return this;

@@ -5281,11 +5593,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField218(value); }

       }

       public Builder SetField218(int value) {

+        PrepareBuilder();

         result.hasField218 = true;

         result.field218_ = value;

         return this;

       }

       public Builder ClearField218() {

+        PrepareBuilder();

         result.hasField218 = false;

         result.field218_ = 0;

         return this;

@@ -5299,11 +5613,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField220(value); }

       }

       public Builder SetField220(int value) {

+        PrepareBuilder();

         result.hasField220 = true;

         result.field220_ = value;

         return this;

       }

       public Builder ClearField220() {

+        PrepareBuilder();

         result.hasField220 = false;

         result.field220_ = 0;

         return this;

@@ -5317,11 +5633,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField221(value); }

       }

       public Builder SetField221(int value) {

+        PrepareBuilder();

         result.hasField221 = true;

         result.field221_ = value;

         return this;

       }

       public Builder ClearField221() {

+        PrepareBuilder();

         result.hasField221 = false;

         result.field221_ = 0;

         return this;

@@ -5335,11 +5653,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField222(value); }

       }

       public Builder SetField222(float value) {

+        PrepareBuilder();

         result.hasField222 = true;

         result.field222_ = value;

         return this;

       }

       public Builder ClearField222() {

+        PrepareBuilder();

         result.hasField222 = false;

         result.field222_ = 0F;

         return this;

@@ -5353,18 +5673,20 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField63(value); }

       }

       public Builder SetField63(int value) {

+        PrepareBuilder();

         result.hasField63 = true;

         result.field63_ = value;

         return this;

       }

       public Builder ClearField63() {

+        PrepareBuilder();

         result.hasField63 = false;

         result.field63_ = 0;

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.SpeedMessage2.Types.Group1> Group1List {

-        get { return result.group1_; }

+        get { return PrepareBuilder().group1_; }

       }

       public int Group1Count {

         get { return result.Group1Count; }

@@ -5374,35 +5696,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetGroup1(int index, global::Google.ProtocolBuffers.TestProtos.SpeedMessage2.Types.Group1 value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.group1_[index] = value;

         return this;

       }

       public Builder SetGroup1(int index, global::Google.ProtocolBuffers.TestProtos.SpeedMessage2.Types.Group1.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.group1_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddGroup1(global::Google.ProtocolBuffers.TestProtos.SpeedMessage2.Types.Group1 value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.group1_.Add(value);

         return this;

       }

       public Builder AddGroup1(global::Google.ProtocolBuffers.TestProtos.SpeedMessage2.Types.Group1.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.group1_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeGroup1(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.SpeedMessage2.Types.Group1> values) {

+        PrepareBuilder();

         result.group1_.Add(values);

         return this;

       }

       public Builder ClearGroup1() {

+        PrepareBuilder();

         result.group1_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> Field128List {

-        get { return result.field128_; }

+        get { return PrepareBuilder().field128_; }

       }

       public int Field128Count {

         get { return result.Field128Count; }

@@ -5412,19 +5740,23 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField128(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.field128_[index] = value;

         return this;

       }

       public Builder AddField128(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.field128_.Add(value);

         return this;

       }

       public Builder AddRangeField128(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.field128_.Add(values);

         return this;

       }

       public Builder ClearField128() {

+        PrepareBuilder();

         result.field128_.Clear();

         return this;

       }

@@ -5437,18 +5769,20 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField131(value); }

       }

       public Builder SetField131(long value) {

+        PrepareBuilder();

         result.hasField131 = true;

         result.field131_ = value;

         return this;

       }

       public Builder ClearField131() {

+        PrepareBuilder();

         result.hasField131 = false;

         result.field131_ = 0L;

         return this;

       }

       

       public pbc::IPopsicleList<string> Field127List {

-        get { return result.field127_; }

+        get { return PrepareBuilder().field127_; }

       }

       public int Field127Count {

         get { return result.Field127Count; }

@@ -5458,19 +5792,23 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetField127(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.field127_[index] = value;

         return this;

       }

       public Builder AddField127(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.field127_.Add(value);

         return this;

       }

       public Builder AddRangeField127(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.field127_.Add(values);

         return this;

       }

       public Builder ClearField127() {

+        PrepareBuilder();

         result.field127_.Clear();

         return this;

       }

@@ -5483,18 +5821,20 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField129(value); }

       }

       public Builder SetField129(int value) {

+        PrepareBuilder();

         result.hasField129 = true;

         result.field129_ = value;

         return this;

       }

       public Builder ClearField129() {

+        PrepareBuilder();

         result.hasField129 = false;

         result.field129_ = 0;

         return this;

       }

       

       public pbc::IPopsicleList<long> Field130List {

-        get { return result.field130_; }

+        get { return PrepareBuilder().field130_; }

       }

       public int Field130Count {

         get { return result.Field130Count; }

@@ -5503,18 +5843,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetField130(index);

       }

       public Builder SetField130(int index, long value) {

+        PrepareBuilder();

         result.field130_[index] = value;

         return this;

       }

       public Builder AddField130(long value) {

+        PrepareBuilder();

         result.field130_.Add(value);

         return this;

       }

       public Builder AddRangeField130(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.field130_.Add(values);

         return this;

       }

       public Builder ClearField130() {

+        PrepareBuilder();

         result.field130_.Clear();

         return this;

       }

@@ -5527,11 +5871,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField205(value); }

       }

       public Builder SetField205(bool value) {

+        PrepareBuilder();

         result.hasField205 = true;

         result.field205_ = value;

         return this;

       }

       public Builder ClearField205() {

+        PrepareBuilder();

         result.hasField205 = false;

         result.field205_ = false;

         return this;

@@ -5545,11 +5891,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField206(value); }

       }

       public Builder SetField206(bool value) {

+        PrepareBuilder();

         result.hasField206 = true;

         result.field206_ = value;

         return this;

       }

       public Builder ClearField206() {

+        PrepareBuilder();

         result.hasField206 = false;

         result.field206_ = false;

         return this;

@@ -5823,7 +6171,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(SpeedMessage2GroupedMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -5833,21 +6181,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new SpeedMessage2GroupedMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(SpeedMessage2GroupedMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      SpeedMessage2GroupedMessage result = new SpeedMessage2GroupedMessage();

+      bool builderIsReadOnly;

+      SpeedMessage2GroupedMessage result;

+      

+      private SpeedMessage2GroupedMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          SpeedMessage2GroupedMessage original = result;

+          result = new SpeedMessage2GroupedMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override SpeedMessage2GroupedMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new SpeedMessage2GroupedMessage();

+        result = DefaultInstance ?? new SpeedMessage2GroupedMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -5859,12 +6234,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override SpeedMessage2GroupedMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        SpeedMessage2GroupedMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -5878,6 +6252,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(SpeedMessage2GroupedMessage other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.SpeedMessage2GroupedMessage.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasField1) {

           Field1 = other.Field1;

         }

@@ -5920,6 +6295,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -6015,11 +6391,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField1(value); }

       }

       public Builder SetField1(float value) {

+        PrepareBuilder();

         result.hasField1 = true;

         result.field1_ = value;

         return this;

       }

       public Builder ClearField1() {

+        PrepareBuilder();

         result.hasField1 = false;

         result.field1_ = 0F;

         return this;

@@ -6033,11 +6411,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField2(value); }

       }

       public Builder SetField2(float value) {

+        PrepareBuilder();

         result.hasField2 = true;

         result.field2_ = value;

         return this;

       }

       public Builder ClearField2() {

+        PrepareBuilder();

         result.hasField2 = false;

         result.field2_ = 0F;

         return this;

@@ -6051,11 +6431,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField3(value); }

       }

       public Builder SetField3(float value) {

+        PrepareBuilder();

         result.hasField3 = true;

         result.field3_ = value;

         return this;

       }

       public Builder ClearField3() {

+        PrepareBuilder();

         result.hasField3 = false;

         result.field3_ = 0F;

         return this;

@@ -6069,11 +6451,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField4(value); }

       }

       public Builder SetField4(bool value) {

+        PrepareBuilder();

         result.hasField4 = true;

         result.field4_ = value;

         return this;

       }

       public Builder ClearField4() {

+        PrepareBuilder();

         result.hasField4 = false;

         result.field4_ = false;

         return this;

@@ -6087,11 +6471,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField5(value); }

       }

       public Builder SetField5(bool value) {

+        PrepareBuilder();

         result.hasField5 = true;

         result.field5_ = value;

         return this;

       }

       public Builder ClearField5() {

+        PrepareBuilder();

         result.hasField5 = false;

         result.field5_ = false;

         return this;

@@ -6105,11 +6491,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField6(value); }

       }

       public Builder SetField6(bool value) {

+        PrepareBuilder();

         result.hasField6 = true;

         result.field6_ = value;

         return this;

       }

       public Builder ClearField6() {

+        PrepareBuilder();

         result.hasField6 = false;

         result.field6_ = true;

         return this;

@@ -6123,11 +6511,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField7(value); }

       }

       public Builder SetField7(bool value) {

+        PrepareBuilder();

         result.hasField7 = true;

         result.field7_ = value;

         return this;

       }

       public Builder ClearField7() {

+        PrepareBuilder();

         result.hasField7 = false;

         result.field7_ = false;

         return this;

@@ -6141,11 +6531,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField8(value); }

       }

       public Builder SetField8(float value) {

+        PrepareBuilder();

         result.hasField8 = true;

         result.field8_ = value;

         return this;

       }

       public Builder ClearField8() {

+        PrepareBuilder();

         result.hasField8 = false;

         result.field8_ = 0F;

         return this;

@@ -6159,11 +6551,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField9(value); }

       }

       public Builder SetField9(bool value) {

+        PrepareBuilder();

         result.hasField9 = true;

         result.field9_ = value;

         return this;

       }

       public Builder ClearField9() {

+        PrepareBuilder();

         result.hasField9 = false;

         result.field9_ = false;

         return this;

@@ -6177,11 +6571,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField10(value); }

       }

       public Builder SetField10(float value) {

+        PrepareBuilder();

         result.hasField10 = true;

         result.field10_ = value;

         return this;

       }

       public Builder ClearField10() {

+        PrepareBuilder();

         result.hasField10 = false;

         result.field10_ = 0F;

         return this;

@@ -6195,11 +6591,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetField11(value); }

       }

       public Builder SetField11(long value) {

+        PrepareBuilder();

         result.hasField11 = true;

         result.field11_ = value;

         return this;

       }

       public Builder ClearField11() {

+        PrepareBuilder();

         result.hasField11 = false;

         result.field11_ = 0L;

         return this;

diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestImportLiteProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestImportLiteProtoFile.cs
index 594c9417..98672cf2 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestImportLiteProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestImportLiteProtoFile.cs
@@ -151,7 +151,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(ImportMessageLite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -161,21 +161,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new ImportMessageLite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(ImportMessageLite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      ImportMessageLite result;

       

-      ImportMessageLite result = new ImportMessageLite();

+      private ImportMessageLite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          ImportMessageLite original = result;

+          result = new ImportMessageLite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override ImportMessageLite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new ImportMessageLite();

+        result = DefaultInstance ?? new ImportMessageLite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override ImportMessageLite DefaultInstanceForType {

@@ -183,12 +210,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override ImportMessageLite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        ImportMessageLite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -202,6 +228,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(ImportMessageLite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.ImportMessageLite.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasD) {

           D = other.D;

         }

@@ -213,6 +240,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -255,11 +283,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetD(value); }

       }

       public Builder SetD(int value) {

+        PrepareBuilder();

         result.hasD = true;

         result.d_ = value;

         return this;

       }

       public Builder ClearD() {

+        PrepareBuilder();

         result.hasD = false;

         result.d_ = 0;

         return this;

diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
index c5da5537..086dda1d 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
@@ -170,7 +170,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(ImportMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -180,21 +180,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new ImportMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(ImportMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      ImportMessage result;

       

-      ImportMessage result = new ImportMessage();

+      private ImportMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          ImportMessage original = result;

+          result = new ImportMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override ImportMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new ImportMessage();

+        result = DefaultInstance ?? new ImportMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -206,12 +233,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override ImportMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        ImportMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -225,6 +251,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(ImportMessage other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.ImportMessage.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasD) {

           D = other.D;

         }

@@ -237,6 +264,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -292,11 +320,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetD(value); }

       }

       public Builder SetD(int value) {

+        PrepareBuilder();

         result.hasD = true;

         result.d_ = value;

         return this;

       }

       public Builder ClearD() {

+        PrepareBuilder();

         result.hasD = false;

         result.d_ = 0;

         return this;

diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs
index 590af6d6..6a90612c 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs
@@ -190,7 +190,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestMessageSet prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -200,21 +200,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestMessageSet();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestMessageSet cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestMessageSet result = new TestMessageSet();

+      bool builderIsReadOnly;

+      TestMessageSet result;

+      

+      private TestMessageSet PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestMessageSet original = result;

+          result = new TestMessageSet();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestMessageSet MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestMessageSet();

+        result = DefaultInstance ?? new TestMessageSet();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -226,12 +253,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestMessageSet BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestMessageSet returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -245,6 +271,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestMessageSet other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestMessageSet.DefaultInstance) return this;

+        PrepareBuilder();

           this.MergeExtensionFields(other);

         this.MergeUnknownFields(other.UnknownFields);

         return this;

@@ -255,6 +282,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -406,7 +434,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestMessageSetContainer prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -416,21 +444,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestMessageSetContainer();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestMessageSetContainer cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestMessageSetContainer result = new TestMessageSetContainer();

+      bool builderIsReadOnly;

+      TestMessageSetContainer result;

+      

+      private TestMessageSetContainer PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestMessageSetContainer original = result;

+          result = new TestMessageSetContainer();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestMessageSetContainer MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestMessageSetContainer();

+        result = DefaultInstance ?? new TestMessageSetContainer();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -442,12 +497,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestMessageSetContainer BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestMessageSetContainer returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -461,6 +515,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestMessageSetContainer other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestMessageSetContainer.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasMessageSet) {

           MergeMessageSet(other.MessageSet);

         }

@@ -473,6 +528,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -534,18 +590,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetMessageSet(global::Google.ProtocolBuffers.TestProtos.TestMessageSet value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasMessageSet = true;

         result.messageSet_ = value;

         return this;

       }

       public Builder SetMessageSet(global::Google.ProtocolBuffers.TestProtos.TestMessageSet.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasMessageSet = true;

         result.messageSet_ = builderForValue.Build();

         return this;

       }

       public Builder MergeMessageSet(global::Google.ProtocolBuffers.TestProtos.TestMessageSet value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasMessageSet &&

             result.messageSet_ != global::Google.ProtocolBuffers.TestProtos.TestMessageSet.DefaultInstance) {

             result.messageSet_ = global::Google.ProtocolBuffers.TestProtos.TestMessageSet.CreateBuilder(result.messageSet_).MergeFrom(value).BuildPartial();

@@ -556,6 +615,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearMessageSet() {

+        PrepareBuilder();

         result.hasMessageSet = false;

         result.messageSet_ = global::Google.ProtocolBuffers.TestProtos.TestMessageSet.DefaultInstance;

         return this;

@@ -671,7 +731,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestMessageSetExtension1 prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -681,21 +741,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestMessageSetExtension1();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestMessageSetExtension1 cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestMessageSetExtension1 result = new TestMessageSetExtension1();

+      bool builderIsReadOnly;

+      TestMessageSetExtension1 result;

+      

+      private TestMessageSetExtension1 PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestMessageSetExtension1 original = result;

+          result = new TestMessageSetExtension1();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestMessageSetExtension1 MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestMessageSetExtension1();

+        result = DefaultInstance ?? new TestMessageSetExtension1();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -707,12 +794,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestMessageSetExtension1 BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestMessageSetExtension1 returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -726,6 +812,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestMessageSetExtension1 other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestMessageSetExtension1.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasI) {

           I = other.I;

         }

@@ -738,6 +825,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -793,11 +881,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetI(value); }

       }

       public Builder SetI(int value) {

+        PrepareBuilder();

         result.hasI = true;

         result.i_ = value;

         return this;

       }

       public Builder ClearI() {

+        PrepareBuilder();

         result.hasI = false;

         result.i_ = 0;

         return this;

@@ -913,7 +1003,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestMessageSetExtension2 prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -923,21 +1013,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestMessageSetExtension2();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestMessageSetExtension2 cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestMessageSetExtension2 result = new TestMessageSetExtension2();

+      bool builderIsReadOnly;

+      TestMessageSetExtension2 result;

+      

+      private TestMessageSetExtension2 PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestMessageSetExtension2 original = result;

+          result = new TestMessageSetExtension2();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestMessageSetExtension2 MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestMessageSetExtension2();

+        result = DefaultInstance ?? new TestMessageSetExtension2();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -949,12 +1066,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestMessageSetExtension2 BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestMessageSetExtension2 returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -968,6 +1084,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestMessageSetExtension2 other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestMessageSetExtension2.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasStr) {

           Str = other.Str;

         }

@@ -980,6 +1097,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1036,11 +1154,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetStr(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasStr = true;

         result.str_ = value;

         return this;

       }

       public Builder ClearStr() {

+        PrepareBuilder();

         result.hasStr = false;

         result.str_ = "";

         return this;

@@ -1205,7 +1325,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(Item prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1215,21 +1335,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new Item();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(Item cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

           

-          Item result = new Item();

+          bool builderIsReadOnly;

+          Item result;

+          

+          private Item PrepareBuilder() {

+            if (builderIsReadOnly) {

+              Item original = result;

+              result = new Item();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override Item MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new Item();

+            result = DefaultInstance ?? new Item();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -1241,12 +1388,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Item BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            Item returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -1260,6 +1406,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(Item other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasTypeId) {

               TypeId = other.TypeId;

             }

@@ -1275,6 +1422,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -1334,11 +1482,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetTypeId(value); }

           }

           public Builder SetTypeId(int value) {

+            PrepareBuilder();

             result.hasTypeId = true;

             result.typeId_ = value;

             return this;

           }

           public Builder ClearTypeId() {

+            PrepareBuilder();

             result.hasTypeId = false;

             result.typeId_ = 0;

             return this;

@@ -1353,11 +1503,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetMessage(pb::ByteString value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasMessage = true;

             result.message_ = value;

             return this;

           }

           public Builder ClearMessage() {

+            PrepareBuilder();

             result.hasMessage = false;

             result.message_ = pb::ByteString.Empty;

             return this;

@@ -1448,7 +1600,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(RawMessageSet prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1458,21 +1610,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new RawMessageSet();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(RawMessageSet cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      RawMessageSet result = new RawMessageSet();

+      bool builderIsReadOnly;

+      RawMessageSet result;

+      

+      private RawMessageSet PrepareBuilder() {

+        if (builderIsReadOnly) {

+          RawMessageSet original = result;

+          result = new RawMessageSet();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override RawMessageSet MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new RawMessageSet();

+        result = DefaultInstance ?? new RawMessageSet();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1484,13 +1663,12 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override RawMessageSet BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.item_.MakeReadOnly();

-        RawMessageSet returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1504,6 +1682,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(RawMessageSet other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.RawMessageSet.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.item_.Count != 0) {

           result.item_.Add(other.item_);

         }

@@ -1516,6 +1695,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1564,7 +1744,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item> ItemList {

-        get { return result.item_; }

+        get { return PrepareBuilder().item_; }

       }

       public int ItemCount {

         get { return result.ItemCount; }

@@ -1574,29 +1754,35 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetItem(int index, global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.item_[index] = value;

         return this;

       }

       public Builder SetItem(int index, global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.item_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddItem(global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.item_.Add(value);

         return this;

       }

       public Builder AddItem(global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.item_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeItem(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item> values) {

+        PrepareBuilder();

         result.item_.Add(values);

         return this;

       }

       public Builder ClearItem() {

+        PrepareBuilder();

         result.item_.Clear();

         return this;

       }

diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestNoGenericServicesProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestNoGenericServicesProtoFile.cs
index 5b652871..2cd2696b 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestNoGenericServicesProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestNoGenericServicesProtoFile.cs
@@ -184,7 +184,7 @@ namespace Google.ProtocolBuffers.TestProtos.NoGenericService {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -194,21 +194,48 @@ namespace Google.ProtocolBuffers.TestProtos.NoGenericService {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestMessage result;

       

-      TestMessage result = new TestMessage();

+      private TestMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestMessage original = result;

+          result = new TestMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestMessage();

+        result = DefaultInstance ?? new TestMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -220,12 +247,11 @@ namespace Google.ProtocolBuffers.TestProtos.NoGenericService {
       }

       

       public override TestMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -239,6 +265,7 @@ namespace Google.ProtocolBuffers.TestProtos.NoGenericService {
       

       public override Builder MergeFrom(TestMessage other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.NoGenericService.TestMessage.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           A = other.A;

         }

@@ -252,6 +279,7 @@ namespace Google.ProtocolBuffers.TestProtos.NoGenericService {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -307,11 +335,13 @@ namespace Google.ProtocolBuffers.TestProtos.NoGenericService {
         set { SetA(value); }

       }

       public Builder SetA(int value) {

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = 0;

         return this;

diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs
index d436afc8..10c464a4 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs
@@ -165,7 +165,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestOptimizedForSize prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -175,21 +175,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestOptimizedForSize();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestOptimizedForSize cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestOptimizedForSize result = new TestOptimizedForSize();

+      bool builderIsReadOnly;

+      TestOptimizedForSize result;

+      

+      private TestOptimizedForSize PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestOptimizedForSize original = result;

+          result = new TestOptimizedForSize();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestOptimizedForSize MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestOptimizedForSize();

+        result = DefaultInstance ?? new TestOptimizedForSize();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -201,12 +228,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestOptimizedForSize BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestOptimizedForSize returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       

@@ -218,11 +244,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetI(value); }

       }

       public Builder SetI(int value) {

+        PrepareBuilder();

         result.hasI = true;

         result.i_ = value;

         return this;

       }

       public Builder ClearI() {

+        PrepareBuilder();

         result.hasI = false;

         result.i_ = 0;

         return this;

@@ -237,18 +265,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetMsg(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasMsg = true;

         result.msg_ = value;

         return this;

       }

       public Builder SetMsg(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasMsg = true;

         result.msg_ = builderForValue.Build();

         return this;

       }

       public Builder MergeMsg(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasMsg &&

             result.msg_ != global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance) {

             result.msg_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.CreateBuilder(result.msg_).MergeFrom(value).BuildPartial();

@@ -259,6 +290,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearMsg() {

+        PrepareBuilder();

         result.hasMsg = false;

         result.msg_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance;

         return this;

@@ -339,7 +371,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestRequiredOptimizedForSize prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -349,21 +381,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestRequiredOptimizedForSize();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestRequiredOptimizedForSize cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestRequiredOptimizedForSize result = new TestRequiredOptimizedForSize();

+      bool builderIsReadOnly;

+      TestRequiredOptimizedForSize result;

+      

+      private TestRequiredOptimizedForSize PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestRequiredOptimizedForSize original = result;

+          result = new TestRequiredOptimizedForSize();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestRequiredOptimizedForSize MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestRequiredOptimizedForSize();

+        result = DefaultInstance ?? new TestRequiredOptimizedForSize();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -375,12 +434,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestRequiredOptimizedForSize BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestRequiredOptimizedForSize returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       

@@ -392,11 +450,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetX(value); }

       }

       public Builder SetX(int value) {

+        PrepareBuilder();

         result.hasX = true;

         result.x_ = value;

         return this;

       }

       public Builder ClearX() {

+        PrepareBuilder();

         result.hasX = false;

         result.x_ = 0;

         return this;

@@ -477,7 +537,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestOptionalOptimizedForSize prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -487,21 +547,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestOptionalOptimizedForSize();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestOptionalOptimizedForSize cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestOptionalOptimizedForSize result = new TestOptionalOptimizedForSize();

+      bool builderIsReadOnly;

+      TestOptionalOptimizedForSize result;

+      

+      private TestOptionalOptimizedForSize PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestOptionalOptimizedForSize original = result;

+          result = new TestOptionalOptimizedForSize();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestOptionalOptimizedForSize MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestOptionalOptimizedForSize();

+        result = DefaultInstance ?? new TestOptionalOptimizedForSize();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -513,12 +600,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestOptionalOptimizedForSize BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestOptionalOptimizedForSize returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       

@@ -531,18 +617,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetO(global::Google.ProtocolBuffers.TestProtos.TestRequiredOptimizedForSize value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasO = true;

         result.o_ = value;

         return this;

       }

       public Builder SetO(global::Google.ProtocolBuffers.TestProtos.TestRequiredOptimizedForSize.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasO = true;

         result.o_ = builderForValue.Build();

         return this;

       }

       public Builder MergeO(global::Google.ProtocolBuffers.TestProtos.TestRequiredOptimizedForSize value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasO &&

             result.o_ != global::Google.ProtocolBuffers.TestProtos.TestRequiredOptimizedForSize.DefaultInstance) {

             result.o_ = global::Google.ProtocolBuffers.TestProtos.TestRequiredOptimizedForSize.CreateBuilder(result.o_).MergeFrom(value).BuildPartial();

@@ -553,6 +642,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearO() {

+        PrepareBuilder();

         result.hasO = false;

         result.o_ = global::Google.ProtocolBuffers.TestProtos.TestRequiredOptimizedForSize.DefaultInstance;

         return this;

diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs
index 86616743..547d712a 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs
@@ -1262,7 +1262,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(NestedMessage prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1272,21 +1272,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new NestedMessage();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(NestedMessage cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          NestedMessage result;

+          

+          private NestedMessage PrepareBuilder() {

+            if (builderIsReadOnly) {

+              NestedMessage original = result;

+              result = new NestedMessage();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

           

-          NestedMessage result = new NestedMessage();

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override NestedMessage MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new NestedMessage();

+            result = DefaultInstance ?? new NestedMessage();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -1298,12 +1325,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override NestedMessage BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            NestedMessage returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -1317,6 +1343,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(NestedMessage other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasBb) {

               Bb = other.Bb;

             }

@@ -1329,6 +1356,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -1384,11 +1412,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetBb(value); }

           }

           public Builder SetBb(int value) {

+            PrepareBuilder();

             result.hasBb = true;

             result.bb_ = value;

             return this;

           }

           public Builder ClearBb() {

+            PrepareBuilder();

             result.hasBb = false;

             result.bb_ = 0;

             return this;

@@ -1502,7 +1532,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(OptionalGroup prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1512,21 +1542,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new OptionalGroup();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(OptionalGroup cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          OptionalGroup result;

+          

+          private OptionalGroup PrepareBuilder() {

+            if (builderIsReadOnly) {

+              OptionalGroup original = result;

+              result = new OptionalGroup();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

           

-          OptionalGroup result = new OptionalGroup();

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override OptionalGroup MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new OptionalGroup();

+            result = DefaultInstance ?? new OptionalGroup();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -1538,12 +1595,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override OptionalGroup BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            OptionalGroup returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -1557,6 +1613,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(OptionalGroup other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasA) {

               A = other.A;

             }

@@ -1569,6 +1626,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -1624,11 +1682,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetA(value); }

           }

           public Builder SetA(int value) {

+            PrepareBuilder();

             result.hasA = true;

             result.a_ = value;

             return this;

           }

           public Builder ClearA() {

+            PrepareBuilder();

             result.hasA = false;

             result.a_ = 0;

             return this;

@@ -1742,7 +1802,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(RepeatedGroup prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1752,21 +1812,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new RepeatedGroup();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(RepeatedGroup cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          RepeatedGroup result;

           

-          RepeatedGroup result = new RepeatedGroup();

+          private RepeatedGroup PrepareBuilder() {

+            if (builderIsReadOnly) {

+              RepeatedGroup original = result;

+              result = new RepeatedGroup();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override RepeatedGroup MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new RepeatedGroup();

+            result = DefaultInstance ?? new RepeatedGroup();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -1778,12 +1865,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override RepeatedGroup BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            RepeatedGroup returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -1797,6 +1883,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(RepeatedGroup other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasA) {

               A = other.A;

             }

@@ -1809,6 +1896,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -1864,11 +1952,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetA(value); }

           }

           public Builder SetA(int value) {

+            PrepareBuilder();

             result.hasA = true;

             result.a_ = value;

             return this;

           }

           public Builder ClearA() {

+            PrepareBuilder();

             result.hasA = false;

             result.a_ = 0;

             return this;

@@ -3185,7 +3275,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestAllTypes prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -3195,21 +3285,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestAllTypes();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestAllTypes cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestAllTypes result;

+      

+      private TestAllTypes PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestAllTypes original = result;

+          result = new TestAllTypes();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestAllTypes result = new TestAllTypes();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestAllTypes MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestAllTypes();

+        result = DefaultInstance ?? new TestAllTypes();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -3221,8 +3338,8 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestAllTypes BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.repeatedInt32_.MakeReadOnly();

         result.repeatedInt64_.MakeReadOnly();

@@ -3248,9 +3365,8 @@ namespace Google.ProtocolBuffers.TestProtos {
         result.repeatedImportEnum_.MakeReadOnly();

         result.repeatedStringPiece_.MakeReadOnly();

         result.repeatedCord_.MakeReadOnly();

-        TestAllTypes returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -3264,6 +3380,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestAllTypes other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestAllTypes.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasOptionalInt32) {

           OptionalInt32 = other.OptionalInt32;

         }

@@ -3477,6 +3594,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -3911,11 +4029,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalInt32(value); }

       }

       public Builder SetOptionalInt32(int value) {

+        PrepareBuilder();

         result.hasOptionalInt32 = true;

         result.optionalInt32_ = value;

         return this;

       }

       public Builder ClearOptionalInt32() {

+        PrepareBuilder();

         result.hasOptionalInt32 = false;

         result.optionalInt32_ = 0;

         return this;

@@ -3929,11 +4049,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalInt64(value); }

       }

       public Builder SetOptionalInt64(long value) {

+        PrepareBuilder();

         result.hasOptionalInt64 = true;

         result.optionalInt64_ = value;

         return this;

       }

       public Builder ClearOptionalInt64() {

+        PrepareBuilder();

         result.hasOptionalInt64 = false;

         result.optionalInt64_ = 0L;

         return this;

@@ -3949,11 +4071,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetOptionalUint32(uint value) {

+        PrepareBuilder();

         result.hasOptionalUint32 = true;

         result.optionalUint32_ = value;

         return this;

       }

       public Builder ClearOptionalUint32() {

+        PrepareBuilder();

         result.hasOptionalUint32 = false;

         result.optionalUint32_ = 0;

         return this;

@@ -3969,11 +4093,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetOptionalUint64(ulong value) {

+        PrepareBuilder();

         result.hasOptionalUint64 = true;

         result.optionalUint64_ = value;

         return this;

       }

       public Builder ClearOptionalUint64() {

+        PrepareBuilder();

         result.hasOptionalUint64 = false;

         result.optionalUint64_ = 0UL;

         return this;

@@ -3987,11 +4113,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalSint32(value); }

       }

       public Builder SetOptionalSint32(int value) {

+        PrepareBuilder();

         result.hasOptionalSint32 = true;

         result.optionalSint32_ = value;

         return this;

       }

       public Builder ClearOptionalSint32() {

+        PrepareBuilder();

         result.hasOptionalSint32 = false;

         result.optionalSint32_ = 0;

         return this;

@@ -4005,11 +4133,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalSint64(value); }

       }

       public Builder SetOptionalSint64(long value) {

+        PrepareBuilder();

         result.hasOptionalSint64 = true;

         result.optionalSint64_ = value;

         return this;

       }

       public Builder ClearOptionalSint64() {

+        PrepareBuilder();

         result.hasOptionalSint64 = false;

         result.optionalSint64_ = 0;

         return this;

@@ -4025,11 +4155,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetOptionalFixed32(uint value) {

+        PrepareBuilder();

         result.hasOptionalFixed32 = true;

         result.optionalFixed32_ = value;

         return this;

       }

       public Builder ClearOptionalFixed32() {

+        PrepareBuilder();

         result.hasOptionalFixed32 = false;

         result.optionalFixed32_ = 0;

         return this;

@@ -4045,11 +4177,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetOptionalFixed64(ulong value) {

+        PrepareBuilder();

         result.hasOptionalFixed64 = true;

         result.optionalFixed64_ = value;

         return this;

       }

       public Builder ClearOptionalFixed64() {

+        PrepareBuilder();

         result.hasOptionalFixed64 = false;

         result.optionalFixed64_ = 0;

         return this;

@@ -4063,11 +4197,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalSfixed32(value); }

       }

       public Builder SetOptionalSfixed32(int value) {

+        PrepareBuilder();

         result.hasOptionalSfixed32 = true;

         result.optionalSfixed32_ = value;

         return this;

       }

       public Builder ClearOptionalSfixed32() {

+        PrepareBuilder();

         result.hasOptionalSfixed32 = false;

         result.optionalSfixed32_ = 0;

         return this;

@@ -4081,11 +4217,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalSfixed64(value); }

       }

       public Builder SetOptionalSfixed64(long value) {

+        PrepareBuilder();

         result.hasOptionalSfixed64 = true;

         result.optionalSfixed64_ = value;

         return this;

       }

       public Builder ClearOptionalSfixed64() {

+        PrepareBuilder();

         result.hasOptionalSfixed64 = false;

         result.optionalSfixed64_ = 0;

         return this;

@@ -4099,11 +4237,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalFloat(value); }

       }

       public Builder SetOptionalFloat(float value) {

+        PrepareBuilder();

         result.hasOptionalFloat = true;

         result.optionalFloat_ = value;

         return this;

       }

       public Builder ClearOptionalFloat() {

+        PrepareBuilder();

         result.hasOptionalFloat = false;

         result.optionalFloat_ = 0F;

         return this;

@@ -4117,11 +4257,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalDouble(value); }

       }

       public Builder SetOptionalDouble(double value) {

+        PrepareBuilder();

         result.hasOptionalDouble = true;

         result.optionalDouble_ = value;

         return this;

       }

       public Builder ClearOptionalDouble() {

+        PrepareBuilder();

         result.hasOptionalDouble = false;

         result.optionalDouble_ = 0D;

         return this;

@@ -4135,11 +4277,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalBool(value); }

       }

       public Builder SetOptionalBool(bool value) {

+        PrepareBuilder();

         result.hasOptionalBool = true;

         result.optionalBool_ = value;

         return this;

       }

       public Builder ClearOptionalBool() {

+        PrepareBuilder();

         result.hasOptionalBool = false;

         result.optionalBool_ = false;

         return this;

@@ -4154,11 +4298,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalString(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalString = true;

         result.optionalString_ = value;

         return this;

       }

       public Builder ClearOptionalString() {

+        PrepareBuilder();

         result.hasOptionalString = false;

         result.optionalString_ = "";

         return this;

@@ -4173,11 +4319,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalBytes(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalBytes = true;

         result.optionalBytes_ = value;

         return this;

       }

       public Builder ClearOptionalBytes() {

+        PrepareBuilder();

         result.hasOptionalBytes = false;

         result.optionalBytes_ = pb::ByteString.Empty;

         return this;

@@ -4192,18 +4340,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalGroup = true;

         result.optionalGroup_ = value;

         return this;

       }

       public Builder SetOptionalGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalGroup = true;

         result.optionalGroup_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalGroup &&

             result.optionalGroup_ != global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup.DefaultInstance) {

             result.optionalGroup_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup.CreateBuilder(result.optionalGroup_).MergeFrom(value).BuildPartial();

@@ -4214,6 +4365,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalGroup() {

+        PrepareBuilder();

         result.hasOptionalGroup = false;

         result.optionalGroup_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup.DefaultInstance;

         return this;

@@ -4228,18 +4380,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalNestedMessage = true;

         result.optionalNestedMessage_ = value;

         return this;

       }

       public Builder SetOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalNestedMessage = true;

         result.optionalNestedMessage_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalNestedMessage &&

             result.optionalNestedMessage_ != global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance) {

             result.optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.CreateBuilder(result.optionalNestedMessage_).MergeFrom(value).BuildPartial();

@@ -4250,6 +4405,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalNestedMessage() {

+        PrepareBuilder();

         result.hasOptionalNestedMessage = false;

         result.optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance;

         return this;

@@ -4264,18 +4420,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalForeignMessage = true;

         result.optionalForeignMessage_ = value;

         return this;

       }

       public Builder SetOptionalForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalForeignMessage = true;

         result.optionalForeignMessage_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalForeignMessage &&

             result.optionalForeignMessage_ != global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance) {

             result.optionalForeignMessage_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.CreateBuilder(result.optionalForeignMessage_).MergeFrom(value).BuildPartial();

@@ -4286,6 +4445,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalForeignMessage() {

+        PrepareBuilder();

         result.hasOptionalForeignMessage = false;

         result.optionalForeignMessage_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance;

         return this;

@@ -4300,18 +4460,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalImportMessage = true;

         result.optionalImportMessage_ = value;

         return this;

       }

       public Builder SetOptionalImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalImportMessage = true;

         result.optionalImportMessage_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalImportMessage &&

             result.optionalImportMessage_ != global::Google.ProtocolBuffers.TestProtos.ImportMessage.DefaultInstance) {

             result.optionalImportMessage_ = global::Google.ProtocolBuffers.TestProtos.ImportMessage.CreateBuilder(result.optionalImportMessage_).MergeFrom(value).BuildPartial();

@@ -4322,6 +4485,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalImportMessage() {

+        PrepareBuilder();

         result.hasOptionalImportMessage = false;

         result.optionalImportMessage_ = global::Google.ProtocolBuffers.TestProtos.ImportMessage.DefaultInstance;

         return this;

@@ -4335,11 +4499,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalNestedEnum(value); }

       }

       public Builder SetOptionalNestedEnum(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum value) {

+        PrepareBuilder();

         result.hasOptionalNestedEnum = true;

         result.optionalNestedEnum_ = value;

         return this;

       }

       public Builder ClearOptionalNestedEnum() {

+        PrepareBuilder();

         result.hasOptionalNestedEnum = false;

         result.optionalNestedEnum_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum.FOO;

         return this;

@@ -4353,11 +4519,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalForeignEnum(value); }

       }

       public Builder SetOptionalForeignEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.hasOptionalForeignEnum = true;

         result.optionalForeignEnum_ = value;

         return this;

       }

       public Builder ClearOptionalForeignEnum() {

+        PrepareBuilder();

         result.hasOptionalForeignEnum = false;

         result.optionalForeignEnum_ = global::Google.ProtocolBuffers.TestProtos.ForeignEnum.FOREIGN_FOO;

         return this;

@@ -4371,11 +4539,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalImportEnum(value); }

       }

       public Builder SetOptionalImportEnum(global::Google.ProtocolBuffers.TestProtos.ImportEnum value) {

+        PrepareBuilder();

         result.hasOptionalImportEnum = true;

         result.optionalImportEnum_ = value;

         return this;

       }

       public Builder ClearOptionalImportEnum() {

+        PrepareBuilder();

         result.hasOptionalImportEnum = false;

         result.optionalImportEnum_ = global::Google.ProtocolBuffers.TestProtos.ImportEnum.IMPORT_FOO;

         return this;

@@ -4390,11 +4560,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalStringPiece(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalStringPiece = true;

         result.optionalStringPiece_ = value;

         return this;

       }

       public Builder ClearOptionalStringPiece() {

+        PrepareBuilder();

         result.hasOptionalStringPiece = false;

         result.optionalStringPiece_ = "";

         return this;

@@ -4409,18 +4581,20 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalCord(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalCord = true;

         result.optionalCord_ = value;

         return this;

       }

       public Builder ClearOptionalCord() {

+        PrepareBuilder();

         result.hasOptionalCord = false;

         result.optionalCord_ = "";

         return this;

       }

       

       public pbc::IPopsicleList<int> RepeatedInt32List {

-        get { return result.repeatedInt32_; }

+        get { return PrepareBuilder().repeatedInt32_; }

       }

       public int RepeatedInt32Count {

         get { return result.RepeatedInt32Count; }

@@ -4429,24 +4603,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedInt32(index);

       }

       public Builder SetRepeatedInt32(int index, int value) {

+        PrepareBuilder();

         result.repeatedInt32_[index] = value;

         return this;

       }

       public Builder AddRepeatedInt32(int value) {

+        PrepareBuilder();

         result.repeatedInt32_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedInt32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.repeatedInt32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedInt32() {

+        PrepareBuilder();

         result.repeatedInt32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> RepeatedInt64List {

-        get { return result.repeatedInt64_; }

+        get { return PrepareBuilder().repeatedInt64_; }

       }

       public int RepeatedInt64Count {

         get { return result.RepeatedInt64Count; }

@@ -4455,25 +4633,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedInt64(index);

       }

       public Builder SetRepeatedInt64(int index, long value) {

+        PrepareBuilder();

         result.repeatedInt64_[index] = value;

         return this;

       }

       public Builder AddRepeatedInt64(long value) {

+        PrepareBuilder();

         result.repeatedInt64_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedInt64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.repeatedInt64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedInt64() {

+        PrepareBuilder();

         result.repeatedInt64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> RepeatedUint32List {

-        get { return result.repeatedUint32_; }

+        get { return PrepareBuilder().repeatedUint32_; }

       }

       public int RepeatedUint32Count {

         get { return result.RepeatedUint32Count; }

@@ -4484,27 +4666,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedUint32(int index, uint value) {

+        PrepareBuilder();

         result.repeatedUint32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedUint32(uint value) {

+        PrepareBuilder();

         result.repeatedUint32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedUint32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.repeatedUint32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedUint32() {

+        PrepareBuilder();

         result.repeatedUint32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> RepeatedUint64List {

-        get { return result.repeatedUint64_; }

+        get { return PrepareBuilder().repeatedUint64_; }

       }

       public int RepeatedUint64Count {

         get { return result.RepeatedUint64Count; }

@@ -4515,26 +4701,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedUint64(int index, ulong value) {

+        PrepareBuilder();

         result.repeatedUint64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedUint64(ulong value) {

+        PrepareBuilder();

         result.repeatedUint64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedUint64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.repeatedUint64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedUint64() {

+        PrepareBuilder();

         result.repeatedUint64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> RepeatedSint32List {

-        get { return result.repeatedSint32_; }

+        get { return PrepareBuilder().repeatedSint32_; }

       }

       public int RepeatedSint32Count {

         get { return result.RepeatedSint32Count; }

@@ -4543,24 +4733,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedSint32(index);

       }

       public Builder SetRepeatedSint32(int index, int value) {

+        PrepareBuilder();

         result.repeatedSint32_[index] = value;

         return this;

       }

       public Builder AddRepeatedSint32(int value) {

+        PrepareBuilder();

         result.repeatedSint32_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedSint32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.repeatedSint32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedSint32() {

+        PrepareBuilder();

         result.repeatedSint32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> RepeatedSint64List {

-        get { return result.repeatedSint64_; }

+        get { return PrepareBuilder().repeatedSint64_; }

       }

       public int RepeatedSint64Count {

         get { return result.RepeatedSint64Count; }

@@ -4569,25 +4763,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedSint64(index);

       }

       public Builder SetRepeatedSint64(int index, long value) {

+        PrepareBuilder();

         result.repeatedSint64_[index] = value;

         return this;

       }

       public Builder AddRepeatedSint64(long value) {

+        PrepareBuilder();

         result.repeatedSint64_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedSint64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.repeatedSint64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedSint64() {

+        PrepareBuilder();

         result.repeatedSint64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> RepeatedFixed32List {

-        get { return result.repeatedFixed32_; }

+        get { return PrepareBuilder().repeatedFixed32_; }

       }

       public int RepeatedFixed32Count {

         get { return result.RepeatedFixed32Count; }

@@ -4598,27 +4796,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedFixed32(int index, uint value) {

+        PrepareBuilder();

         result.repeatedFixed32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedFixed32(uint value) {

+        PrepareBuilder();

         result.repeatedFixed32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedFixed32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.repeatedFixed32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFixed32() {

+        PrepareBuilder();

         result.repeatedFixed32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> RepeatedFixed64List {

-        get { return result.repeatedFixed64_; }

+        get { return PrepareBuilder().repeatedFixed64_; }

       }

       public int RepeatedFixed64Count {

         get { return result.RepeatedFixed64Count; }

@@ -4629,26 +4831,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedFixed64(int index, ulong value) {

+        PrepareBuilder();

         result.repeatedFixed64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedFixed64(ulong value) {

+        PrepareBuilder();

         result.repeatedFixed64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedFixed64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.repeatedFixed64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFixed64() {

+        PrepareBuilder();

         result.repeatedFixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> RepeatedSfixed32List {

-        get { return result.repeatedSfixed32_; }

+        get { return PrepareBuilder().repeatedSfixed32_; }

       }

       public int RepeatedSfixed32Count {

         get { return result.RepeatedSfixed32Count; }

@@ -4657,24 +4863,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedSfixed32(index);

       }

       public Builder SetRepeatedSfixed32(int index, int value) {

+        PrepareBuilder();

         result.repeatedSfixed32_[index] = value;

         return this;

       }

       public Builder AddRepeatedSfixed32(int value) {

+        PrepareBuilder();

         result.repeatedSfixed32_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedSfixed32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.repeatedSfixed32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedSfixed32() {

+        PrepareBuilder();

         result.repeatedSfixed32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> RepeatedSfixed64List {

-        get { return result.repeatedSfixed64_; }

+        get { return PrepareBuilder().repeatedSfixed64_; }

       }

       public int RepeatedSfixed64Count {

         get { return result.RepeatedSfixed64Count; }

@@ -4683,24 +4893,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedSfixed64(index);

       }

       public Builder SetRepeatedSfixed64(int index, long value) {

+        PrepareBuilder();

         result.repeatedSfixed64_[index] = value;

         return this;

       }

       public Builder AddRepeatedSfixed64(long value) {

+        PrepareBuilder();

         result.repeatedSfixed64_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedSfixed64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.repeatedSfixed64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedSfixed64() {

+        PrepareBuilder();

         result.repeatedSfixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<float> RepeatedFloatList {

-        get { return result.repeatedFloat_; }

+        get { return PrepareBuilder().repeatedFloat_; }

       }

       public int RepeatedFloatCount {

         get { return result.RepeatedFloatCount; }

@@ -4709,24 +4923,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedFloat(index);

       }

       public Builder SetRepeatedFloat(int index, float value) {

+        PrepareBuilder();

         result.repeatedFloat_[index] = value;

         return this;

       }

       public Builder AddRepeatedFloat(float value) {

+        PrepareBuilder();

         result.repeatedFloat_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedFloat(scg::IEnumerable<float> values) {

+        PrepareBuilder();

         result.repeatedFloat_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFloat() {

+        PrepareBuilder();

         result.repeatedFloat_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<double> RepeatedDoubleList {

-        get { return result.repeatedDouble_; }

+        get { return PrepareBuilder().repeatedDouble_; }

       }

       public int RepeatedDoubleCount {

         get { return result.RepeatedDoubleCount; }

@@ -4735,24 +4953,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedDouble(index);

       }

       public Builder SetRepeatedDouble(int index, double value) {

+        PrepareBuilder();

         result.repeatedDouble_[index] = value;

         return this;

       }

       public Builder AddRepeatedDouble(double value) {

+        PrepareBuilder();

         result.repeatedDouble_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedDouble(scg::IEnumerable<double> values) {

+        PrepareBuilder();

         result.repeatedDouble_.Add(values);

         return this;

       }

       public Builder ClearRepeatedDouble() {

+        PrepareBuilder();

         result.repeatedDouble_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<bool> RepeatedBoolList {

-        get { return result.repeatedBool_; }

+        get { return PrepareBuilder().repeatedBool_; }

       }

       public int RepeatedBoolCount {

         get { return result.RepeatedBoolCount; }

@@ -4761,24 +4983,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedBool(index);

       }

       public Builder SetRepeatedBool(int index, bool value) {

+        PrepareBuilder();

         result.repeatedBool_[index] = value;

         return this;

       }

       public Builder AddRepeatedBool(bool value) {

+        PrepareBuilder();

         result.repeatedBool_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedBool(scg::IEnumerable<bool> values) {

+        PrepareBuilder();

         result.repeatedBool_.Add(values);

         return this;

       }

       public Builder ClearRepeatedBool() {

+        PrepareBuilder();

         result.repeatedBool_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedStringList {

-        get { return result.repeatedString_; }

+        get { return PrepareBuilder().repeatedString_; }

       }

       public int RepeatedStringCount {

         get { return result.RepeatedStringCount; }

@@ -4788,25 +5014,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedString(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedString_[index] = value;

         return this;

       }

       public Builder AddRepeatedString(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedString_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedString(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedString_.Add(values);

         return this;

       }

       public Builder ClearRepeatedString() {

+        PrepareBuilder();

         result.repeatedString_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<pb::ByteString> RepeatedBytesList {

-        get { return result.repeatedBytes_; }

+        get { return PrepareBuilder().repeatedBytes_; }

       }

       public int RepeatedBytesCount {

         get { return result.RepeatedBytesCount; }

@@ -4816,25 +5046,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedBytes(int index, pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedBytes_[index] = value;

         return this;

       }

       public Builder AddRepeatedBytes(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedBytes_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedBytes(scg::IEnumerable<pb::ByteString> values) {

+        PrepareBuilder();

         result.repeatedBytes_.Add(values);

         return this;

       }

       public Builder ClearRepeatedBytes() {

+        PrepareBuilder();

         result.repeatedBytes_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup> RepeatedGroupList {

-        get { return result.repeatedGroup_; }

+        get { return PrepareBuilder().repeatedGroup_; }

       }

       public int RepeatedGroupCount {

         get { return result.RepeatedGroupCount; }

@@ -4844,35 +5078,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedGroup(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedGroup_[index] = value;

         return this;

       }

       public Builder SetRepeatedGroup(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedGroup_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedGroup_.Add(value);

         return this;

       }

       public Builder AddRepeatedGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedGroup_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedGroup(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup> values) {

+        PrepareBuilder();

         result.repeatedGroup_.Add(values);

         return this;

       }

       public Builder ClearRepeatedGroup() {

+        PrepareBuilder();

         result.repeatedGroup_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage> RepeatedNestedMessageList {

-        get { return result.repeatedNestedMessage_; }

+        get { return PrepareBuilder().repeatedNestedMessage_; }

       }

       public int RepeatedNestedMessageCount {

         get { return result.RepeatedNestedMessageCount; }

@@ -4882,35 +5122,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedNestedMessage(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedNestedMessage_[index] = value;

         return this;

       }

       public Builder SetRepeatedNestedMessage(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedNestedMessage_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedNestedMessage_.Add(value);

         return this;

       }

       public Builder AddRepeatedNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedNestedMessage_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedNestedMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage> values) {

+        PrepareBuilder();

         result.repeatedNestedMessage_.Add(values);

         return this;

       }

       public Builder ClearRepeatedNestedMessage() {

+        PrepareBuilder();

         result.repeatedNestedMessage_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> RepeatedForeignMessageList {

-        get { return result.repeatedForeignMessage_; }

+        get { return PrepareBuilder().repeatedForeignMessage_; }

       }

       public int RepeatedForeignMessageCount {

         get { return result.RepeatedForeignMessageCount; }

@@ -4920,35 +5166,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedForeignMessage(int index, global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedForeignMessage_[index] = value;

         return this;

       }

       public Builder SetRepeatedForeignMessage(int index, global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedForeignMessage_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedForeignMessage_.Add(value);

         return this;

       }

       public Builder AddRepeatedForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedForeignMessage_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedForeignMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> values) {

+        PrepareBuilder();

         result.repeatedForeignMessage_.Add(values);

         return this;

       }

       public Builder ClearRepeatedForeignMessage() {

+        PrepareBuilder();

         result.repeatedForeignMessage_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ImportMessage> RepeatedImportMessageList {

-        get { return result.repeatedImportMessage_; }

+        get { return PrepareBuilder().repeatedImportMessage_; }

       }

       public int RepeatedImportMessageCount {

         get { return result.RepeatedImportMessageCount; }

@@ -4958,35 +5210,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedImportMessage(int index, global::Google.ProtocolBuffers.TestProtos.ImportMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedImportMessage_[index] = value;

         return this;

       }

       public Builder SetRepeatedImportMessage(int index, global::Google.ProtocolBuffers.TestProtos.ImportMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedImportMessage_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedImportMessage_.Add(value);

         return this;

       }

       public Builder AddRepeatedImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedImportMessage_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedImportMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ImportMessage> values) {

+        PrepareBuilder();

         result.repeatedImportMessage_.Add(values);

         return this;

       }

       public Builder ClearRepeatedImportMessage() {

+        PrepareBuilder();

         result.repeatedImportMessage_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum> RepeatedNestedEnumList {

-        get { return result.repeatedNestedEnum_; }

+        get { return PrepareBuilder().repeatedNestedEnum_; }

       }

       public int RepeatedNestedEnumCount {

         get { return result.RepeatedNestedEnumCount; }

@@ -4995,24 +5253,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedNestedEnum(index);

       }

       public Builder SetRepeatedNestedEnum(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum value) {

+        PrepareBuilder();

         result.repeatedNestedEnum_[index] = value;

         return this;

       }

       public Builder AddRepeatedNestedEnum(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum value) {

+        PrepareBuilder();

         result.repeatedNestedEnum_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedNestedEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum> values) {

+        PrepareBuilder();

         result.repeatedNestedEnum_.Add(values);

         return this;

       }

       public Builder ClearRepeatedNestedEnum() {

+        PrepareBuilder();

         result.repeatedNestedEnum_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> RepeatedForeignEnumList {

-        get { return result.repeatedForeignEnum_; }

+        get { return PrepareBuilder().repeatedForeignEnum_; }

       }

       public int RepeatedForeignEnumCount {

         get { return result.RepeatedForeignEnumCount; }

@@ -5021,24 +5283,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedForeignEnum(index);

       }

       public Builder SetRepeatedForeignEnum(int index, global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.repeatedForeignEnum_[index] = value;

         return this;

       }

       public Builder AddRepeatedForeignEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.repeatedForeignEnum_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedForeignEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> values) {

+        PrepareBuilder();

         result.repeatedForeignEnum_.Add(values);

         return this;

       }

       public Builder ClearRepeatedForeignEnum() {

+        PrepareBuilder();

         result.repeatedForeignEnum_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ImportEnum> RepeatedImportEnumList {

-        get { return result.repeatedImportEnum_; }

+        get { return PrepareBuilder().repeatedImportEnum_; }

       }

       public int RepeatedImportEnumCount {

         get { return result.RepeatedImportEnumCount; }

@@ -5047,24 +5313,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedImportEnum(index);

       }

       public Builder SetRepeatedImportEnum(int index, global::Google.ProtocolBuffers.TestProtos.ImportEnum value) {

+        PrepareBuilder();

         result.repeatedImportEnum_[index] = value;

         return this;

       }

       public Builder AddRepeatedImportEnum(global::Google.ProtocolBuffers.TestProtos.ImportEnum value) {

+        PrepareBuilder();

         result.repeatedImportEnum_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedImportEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ImportEnum> values) {

+        PrepareBuilder();

         result.repeatedImportEnum_.Add(values);

         return this;

       }

       public Builder ClearRepeatedImportEnum() {

+        PrepareBuilder();

         result.repeatedImportEnum_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedStringPieceList {

-        get { return result.repeatedStringPiece_; }

+        get { return PrepareBuilder().repeatedStringPiece_; }

       }

       public int RepeatedStringPieceCount {

         get { return result.RepeatedStringPieceCount; }

@@ -5074,25 +5344,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedStringPiece(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedStringPiece_[index] = value;

         return this;

       }

       public Builder AddRepeatedStringPiece(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedStringPiece_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedStringPiece(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedStringPiece_.Add(values);

         return this;

       }

       public Builder ClearRepeatedStringPiece() {

+        PrepareBuilder();

         result.repeatedStringPiece_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedCordList {

-        get { return result.repeatedCord_; }

+        get { return PrepareBuilder().repeatedCord_; }

       }

       public int RepeatedCordCount {

         get { return result.RepeatedCordCount; }

@@ -5102,19 +5376,23 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedCord(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedCord_[index] = value;

         return this;

       }

       public Builder AddRepeatedCord(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedCord_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedCord(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedCord_.Add(values);

         return this;

       }

       public Builder ClearRepeatedCord() {

+        PrepareBuilder();

         result.repeatedCord_.Clear();

         return this;

       }

@@ -5127,11 +5405,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultInt32(value); }

       }

       public Builder SetDefaultInt32(int value) {

+        PrepareBuilder();

         result.hasDefaultInt32 = true;

         result.defaultInt32_ = value;

         return this;

       }

       public Builder ClearDefaultInt32() {

+        PrepareBuilder();

         result.hasDefaultInt32 = false;

         result.defaultInt32_ = 41;

         return this;

@@ -5145,11 +5425,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultInt64(value); }

       }

       public Builder SetDefaultInt64(long value) {

+        PrepareBuilder();

         result.hasDefaultInt64 = true;

         result.defaultInt64_ = value;

         return this;

       }

       public Builder ClearDefaultInt64() {

+        PrepareBuilder();

         result.hasDefaultInt64 = false;

         result.defaultInt64_ = 42L;

         return this;

@@ -5165,11 +5447,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetDefaultUint32(uint value) {

+        PrepareBuilder();

         result.hasDefaultUint32 = true;

         result.defaultUint32_ = value;

         return this;

       }

       public Builder ClearDefaultUint32() {

+        PrepareBuilder();

         result.hasDefaultUint32 = false;

         result.defaultUint32_ = 43;

         return this;

@@ -5185,11 +5469,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetDefaultUint64(ulong value) {

+        PrepareBuilder();

         result.hasDefaultUint64 = true;

         result.defaultUint64_ = value;

         return this;

       }

       public Builder ClearDefaultUint64() {

+        PrepareBuilder();

         result.hasDefaultUint64 = false;

         result.defaultUint64_ = 44UL;

         return this;

@@ -5203,11 +5489,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultSint32(value); }

       }

       public Builder SetDefaultSint32(int value) {

+        PrepareBuilder();

         result.hasDefaultSint32 = true;

         result.defaultSint32_ = value;

         return this;

       }

       public Builder ClearDefaultSint32() {

+        PrepareBuilder();

         result.hasDefaultSint32 = false;

         result.defaultSint32_ = -45;

         return this;

@@ -5221,11 +5509,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultSint64(value); }

       }

       public Builder SetDefaultSint64(long value) {

+        PrepareBuilder();

         result.hasDefaultSint64 = true;

         result.defaultSint64_ = value;

         return this;

       }

       public Builder ClearDefaultSint64() {

+        PrepareBuilder();

         result.hasDefaultSint64 = false;

         result.defaultSint64_ = 46;

         return this;

@@ -5241,11 +5531,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetDefaultFixed32(uint value) {

+        PrepareBuilder();

         result.hasDefaultFixed32 = true;

         result.defaultFixed32_ = value;

         return this;

       }

       public Builder ClearDefaultFixed32() {

+        PrepareBuilder();

         result.hasDefaultFixed32 = false;

         result.defaultFixed32_ = 47;

         return this;

@@ -5261,11 +5553,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetDefaultFixed64(ulong value) {

+        PrepareBuilder();

         result.hasDefaultFixed64 = true;

         result.defaultFixed64_ = value;

         return this;

       }

       public Builder ClearDefaultFixed64() {

+        PrepareBuilder();

         result.hasDefaultFixed64 = false;

         result.defaultFixed64_ = 48;

         return this;

@@ -5279,11 +5573,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultSfixed32(value); }

       }

       public Builder SetDefaultSfixed32(int value) {

+        PrepareBuilder();

         result.hasDefaultSfixed32 = true;

         result.defaultSfixed32_ = value;

         return this;

       }

       public Builder ClearDefaultSfixed32() {

+        PrepareBuilder();

         result.hasDefaultSfixed32 = false;

         result.defaultSfixed32_ = 49;

         return this;

@@ -5297,11 +5593,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultSfixed64(value); }

       }

       public Builder SetDefaultSfixed64(long value) {

+        PrepareBuilder();

         result.hasDefaultSfixed64 = true;

         result.defaultSfixed64_ = value;

         return this;

       }

       public Builder ClearDefaultSfixed64() {

+        PrepareBuilder();

         result.hasDefaultSfixed64 = false;

         result.defaultSfixed64_ = -50;

         return this;

@@ -5315,11 +5613,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultFloat(value); }

       }

       public Builder SetDefaultFloat(float value) {

+        PrepareBuilder();

         result.hasDefaultFloat = true;

         result.defaultFloat_ = value;

         return this;

       }

       public Builder ClearDefaultFloat() {

+        PrepareBuilder();

         result.hasDefaultFloat = false;

         result.defaultFloat_ = 51.5F;

         return this;

@@ -5333,11 +5633,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultDouble(value); }

       }

       public Builder SetDefaultDouble(double value) {

+        PrepareBuilder();

         result.hasDefaultDouble = true;

         result.defaultDouble_ = value;

         return this;

       }

       public Builder ClearDefaultDouble() {

+        PrepareBuilder();

         result.hasDefaultDouble = false;

         result.defaultDouble_ = 52000D;

         return this;

@@ -5351,11 +5653,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultBool(value); }

       }

       public Builder SetDefaultBool(bool value) {

+        PrepareBuilder();

         result.hasDefaultBool = true;

         result.defaultBool_ = value;

         return this;

       }

       public Builder ClearDefaultBool() {

+        PrepareBuilder();

         result.hasDefaultBool = false;

         result.defaultBool_ = true;

         return this;

@@ -5370,11 +5674,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetDefaultString(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDefaultString = true;

         result.defaultString_ = value;

         return this;

       }

       public Builder ClearDefaultString() {

+        PrepareBuilder();

         result.hasDefaultString = false;

         result.defaultString_ = "hello";

         return this;

@@ -5389,11 +5695,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetDefaultBytes(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDefaultBytes = true;

         result.defaultBytes_ = value;

         return this;

       }

       public Builder ClearDefaultBytes() {

+        PrepareBuilder();

         result.hasDefaultBytes = false;

         result.defaultBytes_ = (pb::ByteString) global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Descriptor.Fields[62].DefaultValue;

         return this;

@@ -5407,11 +5715,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultNestedEnum(value); }

       }

       public Builder SetDefaultNestedEnum(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum value) {

+        PrepareBuilder();

         result.hasDefaultNestedEnum = true;

         result.defaultNestedEnum_ = value;

         return this;

       }

       public Builder ClearDefaultNestedEnum() {

+        PrepareBuilder();

         result.hasDefaultNestedEnum = false;

         result.defaultNestedEnum_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum.BAR;

         return this;

@@ -5425,11 +5735,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultForeignEnum(value); }

       }

       public Builder SetDefaultForeignEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.hasDefaultForeignEnum = true;

         result.defaultForeignEnum_ = value;

         return this;

       }

       public Builder ClearDefaultForeignEnum() {

+        PrepareBuilder();

         result.hasDefaultForeignEnum = false;

         result.defaultForeignEnum_ = global::Google.ProtocolBuffers.TestProtos.ForeignEnum.FOREIGN_BAR;

         return this;

@@ -5443,11 +5755,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultImportEnum(value); }

       }

       public Builder SetDefaultImportEnum(global::Google.ProtocolBuffers.TestProtos.ImportEnum value) {

+        PrepareBuilder();

         result.hasDefaultImportEnum = true;

         result.defaultImportEnum_ = value;

         return this;

       }

       public Builder ClearDefaultImportEnum() {

+        PrepareBuilder();

         result.hasDefaultImportEnum = false;

         result.defaultImportEnum_ = global::Google.ProtocolBuffers.TestProtos.ImportEnum.IMPORT_BAR;

         return this;

@@ -5462,11 +5776,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetDefaultStringPiece(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDefaultStringPiece = true;

         result.defaultStringPiece_ = value;

         return this;

       }

       public Builder ClearDefaultStringPiece() {

+        PrepareBuilder();

         result.hasDefaultStringPiece = false;

         result.defaultStringPiece_ = "abc";

         return this;

@@ -5481,11 +5797,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetDefaultCord(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDefaultCord = true;

         result.defaultCord_ = value;

         return this;

       }

       public Builder ClearDefaultCord() {

+        PrepareBuilder();

         result.hasDefaultCord = false;

         result.defaultCord_ = "123";

         return this;

@@ -5601,7 +5919,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestDeprecatedFields prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -5611,21 +5929,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestDeprecatedFields();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestDeprecatedFields cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestDeprecatedFields result;

       

-      TestDeprecatedFields result = new TestDeprecatedFields();

+      private TestDeprecatedFields PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestDeprecatedFields original = result;

+          result = new TestDeprecatedFields();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestDeprecatedFields MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestDeprecatedFields();

+        result = DefaultInstance ?? new TestDeprecatedFields();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -5637,12 +5982,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestDeprecatedFields BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestDeprecatedFields returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -5656,6 +6000,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestDeprecatedFields other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestDeprecatedFields.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasDeprecatedInt32) {

           DeprecatedInt32 = other.DeprecatedInt32;

         }

@@ -5668,6 +6013,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -5726,12 +6072,14 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.ObsoleteAttribute()]

       public Builder SetDeprecatedInt32(int value) {

+        PrepareBuilder();

         result.hasDeprecatedInt32 = true;

         result.deprecatedInt32_ = value;

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder ClearDeprecatedInt32() {

+        PrepareBuilder();

         result.hasDeprecatedInt32 = false;

         result.deprecatedInt32_ = 0;

         return this;

@@ -5845,7 +6193,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(ForeignMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -5855,21 +6203,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new ForeignMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(ForeignMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      ForeignMessage result = new ForeignMessage();

+      bool builderIsReadOnly;

+      ForeignMessage result;

+      

+      private ForeignMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          ForeignMessage original = result;

+          result = new ForeignMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override ForeignMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new ForeignMessage();

+        result = DefaultInstance ?? new ForeignMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -5881,12 +6256,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override ForeignMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        ForeignMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -5900,6 +6274,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(ForeignMessage other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasC) {

           C = other.C;

         }

@@ -5912,6 +6287,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -5967,11 +6343,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetC(value); }

       }

       public Builder SetC(int value) {

+        PrepareBuilder();

         result.hasC = true;

         result.c_ = value;

         return this;

       }

       public Builder ClearC() {

+        PrepareBuilder();

         result.hasC = false;

         result.c_ = 0;

         return this;

@@ -6073,7 +6451,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestAllExtensions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -6083,21 +6461,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestAllExtensions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestAllExtensions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestAllExtensions result = new TestAllExtensions();

+      bool builderIsReadOnly;

+      TestAllExtensions result;

+      

+      private TestAllExtensions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestAllExtensions original = result;

+          result = new TestAllExtensions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestAllExtensions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestAllExtensions();

+        result = DefaultInstance ?? new TestAllExtensions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -6109,12 +6514,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestAllExtensions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestAllExtensions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -6128,6 +6532,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestAllExtensions other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestAllExtensions.DefaultInstance) return this;

+        PrepareBuilder();

           this.MergeExtensionFields(other);

         this.MergeUnknownFields(other.UnknownFields);

         return this;

@@ -6138,6 +6543,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -6289,7 +6695,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(OptionalGroup_extension prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -6299,21 +6705,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new OptionalGroup_extension();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(OptionalGroup_extension cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      OptionalGroup_extension result = new OptionalGroup_extension();

+      bool builderIsReadOnly;

+      OptionalGroup_extension result;

+      

+      private OptionalGroup_extension PrepareBuilder() {

+        if (builderIsReadOnly) {

+          OptionalGroup_extension original = result;

+          result = new OptionalGroup_extension();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override OptionalGroup_extension MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new OptionalGroup_extension();

+        result = DefaultInstance ?? new OptionalGroup_extension();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -6325,12 +6758,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override OptionalGroup_extension BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        OptionalGroup_extension returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -6344,6 +6776,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(OptionalGroup_extension other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.OptionalGroup_extension.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           A = other.A;

         }

@@ -6356,6 +6789,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -6411,11 +6845,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetA(value); }

       }

       public Builder SetA(int value) {

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = 0;

         return this;

@@ -6529,7 +6965,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(RepeatedGroup_extension prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -6539,21 +6975,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new RepeatedGroup_extension();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(RepeatedGroup_extension cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      RepeatedGroup_extension result;

+      

+      private RepeatedGroup_extension PrepareBuilder() {

+        if (builderIsReadOnly) {

+          RepeatedGroup_extension original = result;

+          result = new RepeatedGroup_extension();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      RepeatedGroup_extension result = new RepeatedGroup_extension();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override RepeatedGroup_extension MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new RepeatedGroup_extension();

+        result = DefaultInstance ?? new RepeatedGroup_extension();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -6565,12 +7028,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override RepeatedGroup_extension BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        RepeatedGroup_extension returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -6584,6 +7046,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(RepeatedGroup_extension other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.RepeatedGroup_extension.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           A = other.A;

         }

@@ -6596,6 +7059,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -6651,11 +7115,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetA(value); }

       }

       public Builder SetA(int value) {

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = 0;

         return this;

@@ -6755,7 +7221,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestNestedExtension prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -6765,21 +7231,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestNestedExtension();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestNestedExtension cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestNestedExtension result;

+      

+      private TestNestedExtension PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestNestedExtension original = result;

+          result = new TestNestedExtension();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestNestedExtension result = new TestNestedExtension();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestNestedExtension MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestNestedExtension();

+        result = DefaultInstance ?? new TestNestedExtension();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -6791,12 +7284,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestNestedExtension BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestNestedExtension returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -6810,6 +7302,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestNestedExtension other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestNestedExtension.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -6819,6 +7312,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -7489,7 +7983,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestRequired prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -7499,21 +7993,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestRequired();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestRequired cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestRequired result = new TestRequired();

+      bool builderIsReadOnly;

+      TestRequired result;

+      

+      private TestRequired PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestRequired original = result;

+          result = new TestRequired();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestRequired MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestRequired();

+        result = DefaultInstance ?? new TestRequired();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -7525,12 +8046,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestRequired BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestRequired returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -7544,6 +8064,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestRequired other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestRequired.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           A = other.A;

         }

@@ -7652,6 +8173,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -7835,11 +8357,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetA(value); }

       }

       public Builder SetA(int value) {

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = 0;

         return this;

@@ -7853,11 +8377,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy2(value); }

       }

       public Builder SetDummy2(int value) {

+        PrepareBuilder();

         result.hasDummy2 = true;

         result.dummy2_ = value;

         return this;

       }

       public Builder ClearDummy2() {

+        PrepareBuilder();

         result.hasDummy2 = false;

         result.dummy2_ = 0;

         return this;

@@ -7871,11 +8397,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetB(value); }

       }

       public Builder SetB(int value) {

+        PrepareBuilder();

         result.hasB = true;

         result.b_ = value;

         return this;

       }

       public Builder ClearB() {

+        PrepareBuilder();

         result.hasB = false;

         result.b_ = 0;

         return this;

@@ -7889,11 +8417,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy4(value); }

       }

       public Builder SetDummy4(int value) {

+        PrepareBuilder();

         result.hasDummy4 = true;

         result.dummy4_ = value;

         return this;

       }

       public Builder ClearDummy4() {

+        PrepareBuilder();

         result.hasDummy4 = false;

         result.dummy4_ = 0;

         return this;

@@ -7907,11 +8437,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy5(value); }

       }

       public Builder SetDummy5(int value) {

+        PrepareBuilder();

         result.hasDummy5 = true;

         result.dummy5_ = value;

         return this;

       }

       public Builder ClearDummy5() {

+        PrepareBuilder();

         result.hasDummy5 = false;

         result.dummy5_ = 0;

         return this;

@@ -7925,11 +8457,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy6(value); }

       }

       public Builder SetDummy6(int value) {

+        PrepareBuilder();

         result.hasDummy6 = true;

         result.dummy6_ = value;

         return this;

       }

       public Builder ClearDummy6() {

+        PrepareBuilder();

         result.hasDummy6 = false;

         result.dummy6_ = 0;

         return this;

@@ -7943,11 +8477,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy7(value); }

       }

       public Builder SetDummy7(int value) {

+        PrepareBuilder();

         result.hasDummy7 = true;

         result.dummy7_ = value;

         return this;

       }

       public Builder ClearDummy7() {

+        PrepareBuilder();

         result.hasDummy7 = false;

         result.dummy7_ = 0;

         return this;

@@ -7961,11 +8497,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy8(value); }

       }

       public Builder SetDummy8(int value) {

+        PrepareBuilder();

         result.hasDummy8 = true;

         result.dummy8_ = value;

         return this;

       }

       public Builder ClearDummy8() {

+        PrepareBuilder();

         result.hasDummy8 = false;

         result.dummy8_ = 0;

         return this;

@@ -7979,11 +8517,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy9(value); }

       }

       public Builder SetDummy9(int value) {

+        PrepareBuilder();

         result.hasDummy9 = true;

         result.dummy9_ = value;

         return this;

       }

       public Builder ClearDummy9() {

+        PrepareBuilder();

         result.hasDummy9 = false;

         result.dummy9_ = 0;

         return this;

@@ -7997,11 +8537,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy10(value); }

       }

       public Builder SetDummy10(int value) {

+        PrepareBuilder();

         result.hasDummy10 = true;

         result.dummy10_ = value;

         return this;

       }

       public Builder ClearDummy10() {

+        PrepareBuilder();

         result.hasDummy10 = false;

         result.dummy10_ = 0;

         return this;

@@ -8015,11 +8557,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy11(value); }

       }

       public Builder SetDummy11(int value) {

+        PrepareBuilder();

         result.hasDummy11 = true;

         result.dummy11_ = value;

         return this;

       }

       public Builder ClearDummy11() {

+        PrepareBuilder();

         result.hasDummy11 = false;

         result.dummy11_ = 0;

         return this;

@@ -8033,11 +8577,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy12(value); }

       }

       public Builder SetDummy12(int value) {

+        PrepareBuilder();

         result.hasDummy12 = true;

         result.dummy12_ = value;

         return this;

       }

       public Builder ClearDummy12() {

+        PrepareBuilder();

         result.hasDummy12 = false;

         result.dummy12_ = 0;

         return this;

@@ -8051,11 +8597,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy13(value); }

       }

       public Builder SetDummy13(int value) {

+        PrepareBuilder();

         result.hasDummy13 = true;

         result.dummy13_ = value;

         return this;

       }

       public Builder ClearDummy13() {

+        PrepareBuilder();

         result.hasDummy13 = false;

         result.dummy13_ = 0;

         return this;

@@ -8069,11 +8617,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy14(value); }

       }

       public Builder SetDummy14(int value) {

+        PrepareBuilder();

         result.hasDummy14 = true;

         result.dummy14_ = value;

         return this;

       }

       public Builder ClearDummy14() {

+        PrepareBuilder();

         result.hasDummy14 = false;

         result.dummy14_ = 0;

         return this;

@@ -8087,11 +8637,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy15(value); }

       }

       public Builder SetDummy15(int value) {

+        PrepareBuilder();

         result.hasDummy15 = true;

         result.dummy15_ = value;

         return this;

       }

       public Builder ClearDummy15() {

+        PrepareBuilder();

         result.hasDummy15 = false;

         result.dummy15_ = 0;

         return this;

@@ -8105,11 +8657,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy16(value); }

       }

       public Builder SetDummy16(int value) {

+        PrepareBuilder();

         result.hasDummy16 = true;

         result.dummy16_ = value;

         return this;

       }

       public Builder ClearDummy16() {

+        PrepareBuilder();

         result.hasDummy16 = false;

         result.dummy16_ = 0;

         return this;

@@ -8123,11 +8677,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy17(value); }

       }

       public Builder SetDummy17(int value) {

+        PrepareBuilder();

         result.hasDummy17 = true;

         result.dummy17_ = value;

         return this;

       }

       public Builder ClearDummy17() {

+        PrepareBuilder();

         result.hasDummy17 = false;

         result.dummy17_ = 0;

         return this;

@@ -8141,11 +8697,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy18(value); }

       }

       public Builder SetDummy18(int value) {

+        PrepareBuilder();

         result.hasDummy18 = true;

         result.dummy18_ = value;

         return this;

       }

       public Builder ClearDummy18() {

+        PrepareBuilder();

         result.hasDummy18 = false;

         result.dummy18_ = 0;

         return this;

@@ -8159,11 +8717,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy19(value); }

       }

       public Builder SetDummy19(int value) {

+        PrepareBuilder();

         result.hasDummy19 = true;

         result.dummy19_ = value;

         return this;

       }

       public Builder ClearDummy19() {

+        PrepareBuilder();

         result.hasDummy19 = false;

         result.dummy19_ = 0;

         return this;

@@ -8177,11 +8737,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy20(value); }

       }

       public Builder SetDummy20(int value) {

+        PrepareBuilder();

         result.hasDummy20 = true;

         result.dummy20_ = value;

         return this;

       }

       public Builder ClearDummy20() {

+        PrepareBuilder();

         result.hasDummy20 = false;

         result.dummy20_ = 0;

         return this;

@@ -8195,11 +8757,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy21(value); }

       }

       public Builder SetDummy21(int value) {

+        PrepareBuilder();

         result.hasDummy21 = true;

         result.dummy21_ = value;

         return this;

       }

       public Builder ClearDummy21() {

+        PrepareBuilder();

         result.hasDummy21 = false;

         result.dummy21_ = 0;

         return this;

@@ -8213,11 +8777,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy22(value); }

       }

       public Builder SetDummy22(int value) {

+        PrepareBuilder();

         result.hasDummy22 = true;

         result.dummy22_ = value;

         return this;

       }

       public Builder ClearDummy22() {

+        PrepareBuilder();

         result.hasDummy22 = false;

         result.dummy22_ = 0;

         return this;

@@ -8231,11 +8797,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy23(value); }

       }

       public Builder SetDummy23(int value) {

+        PrepareBuilder();

         result.hasDummy23 = true;

         result.dummy23_ = value;

         return this;

       }

       public Builder ClearDummy23() {

+        PrepareBuilder();

         result.hasDummy23 = false;

         result.dummy23_ = 0;

         return this;

@@ -8249,11 +8817,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy24(value); }

       }

       public Builder SetDummy24(int value) {

+        PrepareBuilder();

         result.hasDummy24 = true;

         result.dummy24_ = value;

         return this;

       }

       public Builder ClearDummy24() {

+        PrepareBuilder();

         result.hasDummy24 = false;

         result.dummy24_ = 0;

         return this;

@@ -8267,11 +8837,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy25(value); }

       }

       public Builder SetDummy25(int value) {

+        PrepareBuilder();

         result.hasDummy25 = true;

         result.dummy25_ = value;

         return this;

       }

       public Builder ClearDummy25() {

+        PrepareBuilder();

         result.hasDummy25 = false;

         result.dummy25_ = 0;

         return this;

@@ -8285,11 +8857,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy26(value); }

       }

       public Builder SetDummy26(int value) {

+        PrepareBuilder();

         result.hasDummy26 = true;

         result.dummy26_ = value;

         return this;

       }

       public Builder ClearDummy26() {

+        PrepareBuilder();

         result.hasDummy26 = false;

         result.dummy26_ = 0;

         return this;

@@ -8303,11 +8877,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy27(value); }

       }

       public Builder SetDummy27(int value) {

+        PrepareBuilder();

         result.hasDummy27 = true;

         result.dummy27_ = value;

         return this;

       }

       public Builder ClearDummy27() {

+        PrepareBuilder();

         result.hasDummy27 = false;

         result.dummy27_ = 0;

         return this;

@@ -8321,11 +8897,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy28(value); }

       }

       public Builder SetDummy28(int value) {

+        PrepareBuilder();

         result.hasDummy28 = true;

         result.dummy28_ = value;

         return this;

       }

       public Builder ClearDummy28() {

+        PrepareBuilder();

         result.hasDummy28 = false;

         result.dummy28_ = 0;

         return this;

@@ -8339,11 +8917,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy29(value); }

       }

       public Builder SetDummy29(int value) {

+        PrepareBuilder();

         result.hasDummy29 = true;

         result.dummy29_ = value;

         return this;

       }

       public Builder ClearDummy29() {

+        PrepareBuilder();

         result.hasDummy29 = false;

         result.dummy29_ = 0;

         return this;

@@ -8357,11 +8937,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy30(value); }

       }

       public Builder SetDummy30(int value) {

+        PrepareBuilder();

         result.hasDummy30 = true;

         result.dummy30_ = value;

         return this;

       }

       public Builder ClearDummy30() {

+        PrepareBuilder();

         result.hasDummy30 = false;

         result.dummy30_ = 0;

         return this;

@@ -8375,11 +8957,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy31(value); }

       }

       public Builder SetDummy31(int value) {

+        PrepareBuilder();

         result.hasDummy31 = true;

         result.dummy31_ = value;

         return this;

       }

       public Builder ClearDummy31() {

+        PrepareBuilder();

         result.hasDummy31 = false;

         result.dummy31_ = 0;

         return this;

@@ -8393,11 +8977,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy32(value); }

       }

       public Builder SetDummy32(int value) {

+        PrepareBuilder();

         result.hasDummy32 = true;

         result.dummy32_ = value;

         return this;

       }

       public Builder ClearDummy32() {

+        PrepareBuilder();

         result.hasDummy32 = false;

         result.dummy32_ = 0;

         return this;

@@ -8411,11 +8997,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetC(value); }

       }

       public Builder SetC(int value) {

+        PrepareBuilder();

         result.hasC = true;

         result.c_ = value;

         return this;

       }

       public Builder ClearC() {

+        PrepareBuilder();

         result.hasC = false;

         result.c_ = 0;

         return this;

@@ -8569,7 +9157,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestRequiredForeign prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -8579,21 +9167,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestRequiredForeign();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestRequiredForeign cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestRequiredForeign result;

       

-      TestRequiredForeign result = new TestRequiredForeign();

+      private TestRequiredForeign PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestRequiredForeign original = result;

+          result = new TestRequiredForeign();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestRequiredForeign MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestRequiredForeign();

+        result = DefaultInstance ?? new TestRequiredForeign();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -8605,13 +9220,12 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestRequiredForeign BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.repeatedMessage_.MakeReadOnly();

-        TestRequiredForeign returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -8625,6 +9239,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestRequiredForeign other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestRequiredForeign.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasOptionalMessage) {

           MergeOptionalMessage(other.OptionalMessage);

         }

@@ -8643,6 +9258,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -8712,18 +9328,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalMessage(global::Google.ProtocolBuffers.TestProtos.TestRequired value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalMessage = true;

         result.optionalMessage_ = value;

         return this;

       }

       public Builder SetOptionalMessage(global::Google.ProtocolBuffers.TestProtos.TestRequired.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalMessage = true;

         result.optionalMessage_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalMessage(global::Google.ProtocolBuffers.TestProtos.TestRequired value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalMessage &&

             result.optionalMessage_ != global::Google.ProtocolBuffers.TestProtos.TestRequired.DefaultInstance) {

             result.optionalMessage_ = global::Google.ProtocolBuffers.TestProtos.TestRequired.CreateBuilder(result.optionalMessage_).MergeFrom(value).BuildPartial();

@@ -8734,13 +9353,14 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalMessage() {

+        PrepareBuilder();

         result.hasOptionalMessage = false;

         result.optionalMessage_ = global::Google.ProtocolBuffers.TestProtos.TestRequired.DefaultInstance;

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestRequired> RepeatedMessageList {

-        get { return result.repeatedMessage_; }

+        get { return PrepareBuilder().repeatedMessage_; }

       }

       public int RepeatedMessageCount {

         get { return result.RepeatedMessageCount; }

@@ -8750,29 +9370,35 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedMessage(int index, global::Google.ProtocolBuffers.TestProtos.TestRequired value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedMessage_[index] = value;

         return this;

       }

       public Builder SetRepeatedMessage(int index, global::Google.ProtocolBuffers.TestProtos.TestRequired.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedMessage_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedMessage(global::Google.ProtocolBuffers.TestProtos.TestRequired value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedMessage_.Add(value);

         return this;

       }

       public Builder AddRepeatedMessage(global::Google.ProtocolBuffers.TestProtos.TestRequired.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedMessage_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestRequired> values) {

+        PrepareBuilder();

         result.repeatedMessage_.Add(values);

         return this;

       }

       public Builder ClearRepeatedMessage() {

+        PrepareBuilder();

         result.repeatedMessage_.Clear();

         return this;

       }

@@ -8785,11 +9411,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy(value); }

       }

       public Builder SetDummy(int value) {

+        PrepareBuilder();

         result.hasDummy = true;

         result.dummy_ = value;

         return this;

       }

       public Builder ClearDummy() {

+        PrepareBuilder();

         result.hasDummy = false;

         result.dummy_ = 0;

         return this;

@@ -8903,7 +9531,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestForeignNested prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -8913,21 +9541,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestForeignNested();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestForeignNested cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestForeignNested result = new TestForeignNested();

+      bool builderIsReadOnly;

+      TestForeignNested result;

+      

+      private TestForeignNested PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestForeignNested original = result;

+          result = new TestForeignNested();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestForeignNested MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestForeignNested();

+        result = DefaultInstance ?? new TestForeignNested();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -8939,12 +9594,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestForeignNested BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestForeignNested returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -8958,6 +9612,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestForeignNested other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestForeignNested.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasForeignNested) {

           MergeForeignNested(other.ForeignNested);

         }

@@ -8970,6 +9625,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -9031,18 +9687,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetForeignNested(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasForeignNested = true;

         result.foreignNested_ = value;

         return this;

       }

       public Builder SetForeignNested(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasForeignNested = true;

         result.foreignNested_ = builderForValue.Build();

         return this;

       }

       public Builder MergeForeignNested(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasForeignNested &&

             result.foreignNested_ != global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance) {

             result.foreignNested_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.CreateBuilder(result.foreignNested_).MergeFrom(value).BuildPartial();

@@ -9053,6 +9712,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearForeignNested() {

+        PrepareBuilder();

         result.hasForeignNested = false;

         result.foreignNested_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance;

         return this;

@@ -9150,7 +9810,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestEmptyMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -9160,21 +9820,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestEmptyMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestEmptyMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestEmptyMessage result;

+      

+      private TestEmptyMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestEmptyMessage original = result;

+          result = new TestEmptyMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestEmptyMessage result = new TestEmptyMessage();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestEmptyMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestEmptyMessage();

+        result = DefaultInstance ?? new TestEmptyMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -9186,12 +9873,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestEmptyMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestEmptyMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -9205,6 +9891,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestEmptyMessage other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestEmptyMessage.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -9214,6 +9901,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -9353,7 +10041,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestEmptyMessageWithExtensions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -9363,21 +10051,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestEmptyMessageWithExtensions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestEmptyMessageWithExtensions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestEmptyMessageWithExtensions result = new TestEmptyMessageWithExtensions();

+      bool builderIsReadOnly;

+      TestEmptyMessageWithExtensions result;

+      

+      private TestEmptyMessageWithExtensions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestEmptyMessageWithExtensions original = result;

+          result = new TestEmptyMessageWithExtensions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestEmptyMessageWithExtensions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestEmptyMessageWithExtensions();

+        result = DefaultInstance ?? new TestEmptyMessageWithExtensions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -9389,12 +10104,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestEmptyMessageWithExtensions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestEmptyMessageWithExtensions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -9408,6 +10122,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestEmptyMessageWithExtensions other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestEmptyMessageWithExtensions.DefaultInstance) return this;

+        PrepareBuilder();

           this.MergeExtensionFields(other);

         this.MergeUnknownFields(other.UnknownFields);

         return this;

@@ -9418,6 +10133,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -9559,7 +10275,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestMultipleExtensionRanges prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -9569,21 +10285,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestMultipleExtensionRanges();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestMultipleExtensionRanges cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestMultipleExtensionRanges result;

+      

+      private TestMultipleExtensionRanges PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestMultipleExtensionRanges original = result;

+          result = new TestMultipleExtensionRanges();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestMultipleExtensionRanges result = new TestMultipleExtensionRanges();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestMultipleExtensionRanges MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestMultipleExtensionRanges();

+        result = DefaultInstance ?? new TestMultipleExtensionRanges();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -9595,12 +10338,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestMultipleExtensionRanges BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestMultipleExtensionRanges returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -9614,6 +10356,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestMultipleExtensionRanges other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestMultipleExtensionRanges.DefaultInstance) return this;

+        PrepareBuilder();

           this.MergeExtensionFields(other);

         this.MergeUnknownFields(other.UnknownFields);

         return this;

@@ -9624,6 +10367,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -9791,7 +10535,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestReallyLargeTagNumber prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -9801,21 +10545,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestReallyLargeTagNumber();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestReallyLargeTagNumber cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestReallyLargeTagNumber result;

+      

+      private TestReallyLargeTagNumber PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestReallyLargeTagNumber original = result;

+          result = new TestReallyLargeTagNumber();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestReallyLargeTagNumber result = new TestReallyLargeTagNumber();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestReallyLargeTagNumber MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestReallyLargeTagNumber();

+        result = DefaultInstance ?? new TestReallyLargeTagNumber();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -9827,12 +10598,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestReallyLargeTagNumber BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestReallyLargeTagNumber returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -9846,6 +10616,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestReallyLargeTagNumber other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestReallyLargeTagNumber.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           A = other.A;

         }

@@ -9861,6 +10632,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -9920,11 +10692,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetA(value); }

       }

       public Builder SetA(int value) {

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = 0;

         return this;

@@ -9938,11 +10712,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetBb(value); }

       }

       public Builder SetBb(int value) {

+        PrepareBuilder();

         result.hasBb = true;

         result.bb_ = value;

         return this;

       }

       public Builder ClearBb() {

+        PrepareBuilder();

         result.hasBb = false;

         result.bb_ = 0;

         return this;

@@ -10072,7 +10848,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestRecursiveMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -10082,21 +10858,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestRecursiveMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestRecursiveMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestRecursiveMessage result = new TestRecursiveMessage();

+      bool builderIsReadOnly;

+      TestRecursiveMessage result;

+      

+      private TestRecursiveMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestRecursiveMessage original = result;

+          result = new TestRecursiveMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestRecursiveMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestRecursiveMessage();

+        result = DefaultInstance ?? new TestRecursiveMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -10108,12 +10911,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestRecursiveMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestRecursiveMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -10127,6 +10929,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestRecursiveMessage other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           MergeA(other.A);

         }

@@ -10142,6 +10945,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -10207,18 +11011,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetA(global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder SetA(global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = builderForValue.Build();

         return this;

       }

       public Builder MergeA(global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasA &&

             result.a_ != global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage.DefaultInstance) {

             result.a_ = global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage.CreateBuilder(result.a_).MergeFrom(value).BuildPartial();

@@ -10229,6 +11036,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage.DefaultInstance;

         return this;

@@ -10242,11 +11050,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetI(value); }

       }

       public Builder SetI(int value) {

+        PrepareBuilder();

         result.hasI = true;

         result.i_ = value;

         return this;

       }

       public Builder ClearI() {

+        PrepareBuilder();

         result.hasI = false;

         result.i_ = 0;

         return this;

@@ -10360,7 +11170,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestMutualRecursionA prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -10370,21 +11180,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestMutualRecursionA();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestMutualRecursionA cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestMutualRecursionA result;

+      

+      private TestMutualRecursionA PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestMutualRecursionA original = result;

+          result = new TestMutualRecursionA();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestMutualRecursionA result = new TestMutualRecursionA();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestMutualRecursionA MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestMutualRecursionA();

+        result = DefaultInstance ?? new TestMutualRecursionA();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -10396,12 +11233,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestMutualRecursionA BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestMutualRecursionA returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -10415,6 +11251,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestMutualRecursionA other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasBb) {

           MergeBb(other.Bb);

         }

@@ -10427,6 +11264,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -10488,18 +11326,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetBb(global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasBb = true;

         result.bb_ = value;

         return this;

       }

       public Builder SetBb(global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasBb = true;

         result.bb_ = builderForValue.Build();

         return this;

       }

       public Builder MergeBb(global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasBb &&

             result.bb_ != global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB.DefaultInstance) {

             result.bb_ = global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB.CreateBuilder(result.bb_).MergeFrom(value).BuildPartial();

@@ -10510,6 +11351,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearBb() {

+        PrepareBuilder();

         result.hasBb = false;

         result.bb_ = global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB.DefaultInstance;

         return this;

@@ -10639,7 +11481,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestMutualRecursionB prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -10649,21 +11491,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestMutualRecursionB();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestMutualRecursionB cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestMutualRecursionB result = new TestMutualRecursionB();

+      bool builderIsReadOnly;

+      TestMutualRecursionB result;

+      

+      private TestMutualRecursionB PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestMutualRecursionB original = result;

+          result = new TestMutualRecursionB();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestMutualRecursionB MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestMutualRecursionB();

+        result = DefaultInstance ?? new TestMutualRecursionB();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -10675,12 +11544,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestMutualRecursionB BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestMutualRecursionB returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -10694,6 +11562,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestMutualRecursionB other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           MergeA(other.A);

         }

@@ -10709,6 +11578,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -10774,18 +11644,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetA(global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder SetA(global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = builderForValue.Build();

         return this;

       }

       public Builder MergeA(global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasA &&

             result.a_ != global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA.DefaultInstance) {

             result.a_ = global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA.CreateBuilder(result.a_).MergeFrom(value).BuildPartial();

@@ -10796,6 +11669,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA.DefaultInstance;

         return this;

@@ -10809,11 +11683,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalInt32(value); }

       }

       public Builder SetOptionalInt32(int value) {

+        PrepareBuilder();

         result.hasOptionalInt32 = true;

         result.optionalInt32_ = value;

         return this;

       }

       public Builder ClearOptionalInt32() {

+        PrepareBuilder();

         result.hasOptionalInt32 = false;

         result.optionalInt32_ = 0;

         return this;

@@ -10960,7 +11836,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(Foo prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -10970,21 +11846,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new Foo();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(Foo cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          Foo result;

           

-          Foo result = new Foo();

+          private Foo PrepareBuilder() {

+            if (builderIsReadOnly) {

+              Foo original = result;

+              result = new Foo();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override Foo MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new Foo();

+            result = DefaultInstance ?? new Foo();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -10996,12 +11899,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Foo BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            Foo returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -11015,6 +11917,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(Foo other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasA) {

               A = other.A;

             }

@@ -11027,6 +11930,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -11082,11 +11986,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetA(value); }

           }

           public Builder SetA(int value) {

+            PrepareBuilder();

             result.hasA = true;

             result.a_ = value;

             return this;

           }

           public Builder ClearA() {

+            PrepareBuilder();

             result.hasA = false;

             result.a_ = 0;

             return this;

@@ -11200,7 +12106,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(Bar prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -11210,21 +12116,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new Bar();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(Bar cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

           

-          Bar result = new Bar();

+          bool builderIsReadOnly;

+          Bar result;

+          

+          private Bar PrepareBuilder() {

+            if (builderIsReadOnly) {

+              Bar original = result;

+              result = new Bar();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override Bar MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new Bar();

+            result = DefaultInstance ?? new Bar();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -11236,12 +12169,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Bar BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            Bar returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -11255,6 +12187,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(Bar other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasA) {

               A = other.A;

             }

@@ -11267,6 +12200,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -11322,11 +12256,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetA(value); }

           }

           public Builder SetA(int value) {

+            PrepareBuilder();

             result.hasA = true;

             result.a_ = value;

             return this;

           }

           public Builder ClearA() {

+            PrepareBuilder();

             result.hasA = false;

             result.a_ = 0;

             return this;

@@ -11447,7 +12383,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestDupFieldNumber prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -11457,21 +12393,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestDupFieldNumber();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestDupFieldNumber cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestDupFieldNumber result = new TestDupFieldNumber();

+      bool builderIsReadOnly;

+      TestDupFieldNumber result;

+      

+      private TestDupFieldNumber PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestDupFieldNumber original = result;

+          result = new TestDupFieldNumber();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestDupFieldNumber MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestDupFieldNumber();

+        result = DefaultInstance ?? new TestDupFieldNumber();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -11483,12 +12446,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestDupFieldNumber BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestDupFieldNumber returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -11502,6 +12464,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestDupFieldNumber other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           A = other.A;

         }

@@ -11520,6 +12483,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -11593,11 +12557,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetA(value); }

       }

       public Builder SetA(int value) {

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = 0;

         return this;

@@ -11612,18 +12578,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetFoo(global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasFoo = true;

         result.foo_ = value;

         return this;

       }

       public Builder SetFoo(global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasFoo = true;

         result.foo_ = builderForValue.Build();

         return this;

       }

       public Builder MergeFoo(global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasFoo &&

             result.foo_ != global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo.DefaultInstance) {

             result.foo_ = global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo.CreateBuilder(result.foo_).MergeFrom(value).BuildPartial();

@@ -11634,6 +12603,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearFoo() {

+        PrepareBuilder();

         result.hasFoo = false;

         result.foo_ = global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo.DefaultInstance;

         return this;

@@ -11648,18 +12618,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetBar(global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasBar = true;

         result.bar_ = value;

         return this;

       }

       public Builder SetBar(global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasBar = true;

         result.bar_ = builderForValue.Build();

         return this;

       }

       public Builder MergeBar(global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasBar &&

             result.bar_ != global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar.DefaultInstance) {

             result.bar_ = global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar.CreateBuilder(result.bar_).MergeFrom(value).BuildPartial();

@@ -11670,6 +12643,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearBar() {

+        PrepareBuilder();

         result.hasBar = false;

         result.bar_ = global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar.DefaultInstance;

         return this;

@@ -11841,7 +12815,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(NestedMessage prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -11851,21 +12825,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new NestedMessage();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(NestedMessage cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          NestedMessage result;

+          

+          private NestedMessage PrepareBuilder() {

+            if (builderIsReadOnly) {

+              NestedMessage original = result;

+              result = new NestedMessage();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

           

-          NestedMessage result = new NestedMessage();

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override NestedMessage MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new NestedMessage();

+            result = DefaultInstance ?? new NestedMessage();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -11877,14 +12878,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override NestedMessage BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

             result.nestedmessageRepeatedInt32_.MakeReadOnly();

             result.nestedmessageRepeatedForeignmessage_.MakeReadOnly();

-            NestedMessage returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -11898,6 +12898,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(NestedMessage other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.nestedmessageRepeatedInt32_.Count != 0) {

               result.nestedmessageRepeatedInt32_.Add(other.nestedmessageRepeatedInt32_);

             }

@@ -11913,6 +12914,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -11966,7 +12968,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           

           public pbc::IPopsicleList<int> NestedmessageRepeatedInt32List {

-            get { return result.nestedmessageRepeatedInt32_; }

+            get { return PrepareBuilder().nestedmessageRepeatedInt32_; }

           }

           public int NestedmessageRepeatedInt32Count {

             get { return result.NestedmessageRepeatedInt32Count; }

@@ -11975,24 +12977,28 @@ namespace Google.ProtocolBuffers.TestProtos {
             return result.GetNestedmessageRepeatedInt32(index);

           }

           public Builder SetNestedmessageRepeatedInt32(int index, int value) {

+            PrepareBuilder();

             result.nestedmessageRepeatedInt32_[index] = value;

             return this;

           }

           public Builder AddNestedmessageRepeatedInt32(int value) {

+            PrepareBuilder();

             result.nestedmessageRepeatedInt32_.Add(value);

             return this;

           }

           public Builder AddRangeNestedmessageRepeatedInt32(scg::IEnumerable<int> values) {

+            PrepareBuilder();

             result.nestedmessageRepeatedInt32_.Add(values);

             return this;

           }

           public Builder ClearNestedmessageRepeatedInt32() {

+            PrepareBuilder();

             result.nestedmessageRepeatedInt32_.Clear();

             return this;

           }

           

           public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> NestedmessageRepeatedForeignmessageList {

-            get { return result.nestedmessageRepeatedForeignmessage_; }

+            get { return PrepareBuilder().nestedmessageRepeatedForeignmessage_; }

           }

           public int NestedmessageRepeatedForeignmessageCount {

             get { return result.NestedmessageRepeatedForeignmessageCount; }

@@ -12002,29 +13008,35 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetNestedmessageRepeatedForeignmessage(int index, global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.nestedmessageRepeatedForeignmessage_[index] = value;

             return this;

           }

           public Builder SetNestedmessageRepeatedForeignmessage(int index, global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

             pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+            PrepareBuilder();

             result.nestedmessageRepeatedForeignmessage_[index] = builderForValue.Build();

             return this;

           }

           public Builder AddNestedmessageRepeatedForeignmessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.nestedmessageRepeatedForeignmessage_.Add(value);

             return this;

           }

           public Builder AddNestedmessageRepeatedForeignmessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

             pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+            PrepareBuilder();

             result.nestedmessageRepeatedForeignmessage_.Add(builderForValue.Build());

             return this;

           }

           public Builder AddRangeNestedmessageRepeatedForeignmessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> values) {

+            PrepareBuilder();

             result.nestedmessageRepeatedForeignmessage_.Add(values);

             return this;

           }

           public Builder ClearNestedmessageRepeatedForeignmessage() {

+            PrepareBuilder();

             result.nestedmessageRepeatedForeignmessage_.Clear();

             return this;

           }

@@ -12112,7 +13124,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestNestedMessageHasBits prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -12122,21 +13134,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestNestedMessageHasBits();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestNestedMessageHasBits cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestNestedMessageHasBits result = new TestNestedMessageHasBits();

+      bool builderIsReadOnly;

+      TestNestedMessageHasBits result;

+      

+      private TestNestedMessageHasBits PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestNestedMessageHasBits original = result;

+          result = new TestNestedMessageHasBits();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestNestedMessageHasBits MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestNestedMessageHasBits();

+        result = DefaultInstance ?? new TestNestedMessageHasBits();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -12148,12 +13187,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestNestedMessageHasBits BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestNestedMessageHasBits returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -12167,6 +13205,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestNestedMessageHasBits other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasOptionalNestedMessage) {

           MergeOptionalNestedMessage(other.OptionalNestedMessage);

         }

@@ -12179,6 +13218,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -12240,18 +13280,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalNestedMessage = true;

         result.optionalNestedMessage_ = value;

         return this;

       }

       public Builder SetOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalNestedMessage = true;

         result.optionalNestedMessage_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalNestedMessage &&

             result.optionalNestedMessage_ != global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage.DefaultInstance) {

             result.optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage.CreateBuilder(result.optionalNestedMessage_).MergeFrom(value).BuildPartial();

@@ -12262,6 +13305,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalNestedMessage() {

+        PrepareBuilder();

         result.hasOptionalNestedMessage = false;

         result.optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage.DefaultInstance;

         return this;

@@ -12590,7 +13634,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestCamelCaseFieldNames prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -12600,21 +13644,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestCamelCaseFieldNames();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestCamelCaseFieldNames cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestCamelCaseFieldNames result;

+      

+      private TestCamelCaseFieldNames PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestCamelCaseFieldNames original = result;

+          result = new TestCamelCaseFieldNames();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestCamelCaseFieldNames result = new TestCamelCaseFieldNames();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestCamelCaseFieldNames MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestCamelCaseFieldNames();

+        result = DefaultInstance ?? new TestCamelCaseFieldNames();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -12626,8 +13697,8 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestCamelCaseFieldNames BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.repeatedPrimitiveField_.MakeReadOnly();

         result.repeatedStringField_.MakeReadOnly();

@@ -12635,9 +13706,8 @@ namespace Google.ProtocolBuffers.TestProtos {
         result.repeatedMessageField_.MakeReadOnly();

         result.repeatedStringPieceField_.MakeReadOnly();

         result.repeatedCordField_.MakeReadOnly();

-        TestCamelCaseFieldNames returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -12651,6 +13721,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestCamelCaseFieldNames other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestCamelCaseFieldNames.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasPrimitiveField) {

           PrimitiveField = other.PrimitiveField;

         }

@@ -12696,6 +13767,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -12819,11 +13891,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetPrimitiveField(value); }

       }

       public Builder SetPrimitiveField(int value) {

+        PrepareBuilder();

         result.hasPrimitiveField = true;

         result.primitiveField_ = value;

         return this;

       }

       public Builder ClearPrimitiveField() {

+        PrepareBuilder();

         result.hasPrimitiveField = false;

         result.primitiveField_ = 0;

         return this;

@@ -12838,11 +13912,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetStringField(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasStringField = true;

         result.stringField_ = value;

         return this;

       }

       public Builder ClearStringField() {

+        PrepareBuilder();

         result.hasStringField = false;

         result.stringField_ = "";

         return this;

@@ -12856,11 +13932,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetEnumField(value); }

       }

       public Builder SetEnumField(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.hasEnumField = true;

         result.enumField_ = value;

         return this;

       }

       public Builder ClearEnumField() {

+        PrepareBuilder();

         result.hasEnumField = false;

         result.enumField_ = global::Google.ProtocolBuffers.TestProtos.ForeignEnum.FOREIGN_FOO;

         return this;

@@ -12875,18 +13953,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetMessageField(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasMessageField = true;

         result.messageField_ = value;

         return this;

       }

       public Builder SetMessageField(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasMessageField = true;

         result.messageField_ = builderForValue.Build();

         return this;

       }

       public Builder MergeMessageField(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasMessageField &&

             result.messageField_ != global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance) {

             result.messageField_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.CreateBuilder(result.messageField_).MergeFrom(value).BuildPartial();

@@ -12897,6 +13978,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearMessageField() {

+        PrepareBuilder();

         result.hasMessageField = false;

         result.messageField_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance;

         return this;

@@ -12911,11 +13993,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetStringPieceField(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasStringPieceField = true;

         result.stringPieceField_ = value;

         return this;

       }

       public Builder ClearStringPieceField() {

+        PrepareBuilder();

         result.hasStringPieceField = false;

         result.stringPieceField_ = "";

         return this;

@@ -12930,18 +14014,20 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetCordField(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasCordField = true;

         result.cordField_ = value;

         return this;

       }

       public Builder ClearCordField() {

+        PrepareBuilder();

         result.hasCordField = false;

         result.cordField_ = "";

         return this;

       }

       

       public pbc::IPopsicleList<int> RepeatedPrimitiveFieldList {

-        get { return result.repeatedPrimitiveField_; }

+        get { return PrepareBuilder().repeatedPrimitiveField_; }

       }

       public int RepeatedPrimitiveFieldCount {

         get { return result.RepeatedPrimitiveFieldCount; }

@@ -12950,24 +14036,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedPrimitiveField(index);

       }

       public Builder SetRepeatedPrimitiveField(int index, int value) {

+        PrepareBuilder();

         result.repeatedPrimitiveField_[index] = value;

         return this;

       }

       public Builder AddRepeatedPrimitiveField(int value) {

+        PrepareBuilder();

         result.repeatedPrimitiveField_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedPrimitiveField(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.repeatedPrimitiveField_.Add(values);

         return this;

       }

       public Builder ClearRepeatedPrimitiveField() {

+        PrepareBuilder();

         result.repeatedPrimitiveField_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedStringFieldList {

-        get { return result.repeatedStringField_; }

+        get { return PrepareBuilder().repeatedStringField_; }

       }

       public int RepeatedStringFieldCount {

         get { return result.RepeatedStringFieldCount; }

@@ -12977,25 +14067,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedStringField(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedStringField_[index] = value;

         return this;

       }

       public Builder AddRepeatedStringField(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedStringField_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedStringField(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedStringField_.Add(values);

         return this;

       }

       public Builder ClearRepeatedStringField() {

+        PrepareBuilder();

         result.repeatedStringField_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> RepeatedEnumFieldList {

-        get { return result.repeatedEnumField_; }

+        get { return PrepareBuilder().repeatedEnumField_; }

       }

       public int RepeatedEnumFieldCount {

         get { return result.RepeatedEnumFieldCount; }

@@ -13004,24 +14098,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedEnumField(index);

       }

       public Builder SetRepeatedEnumField(int index, global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.repeatedEnumField_[index] = value;

         return this;

       }

       public Builder AddRepeatedEnumField(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.repeatedEnumField_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedEnumField(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> values) {

+        PrepareBuilder();

         result.repeatedEnumField_.Add(values);

         return this;

       }

       public Builder ClearRepeatedEnumField() {

+        PrepareBuilder();

         result.repeatedEnumField_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> RepeatedMessageFieldList {

-        get { return result.repeatedMessageField_; }

+        get { return PrepareBuilder().repeatedMessageField_; }

       }

       public int RepeatedMessageFieldCount {

         get { return result.RepeatedMessageFieldCount; }

@@ -13031,35 +14129,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedMessageField(int index, global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedMessageField_[index] = value;

         return this;

       }

       public Builder SetRepeatedMessageField(int index, global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedMessageField_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedMessageField(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedMessageField_.Add(value);

         return this;

       }

       public Builder AddRepeatedMessageField(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedMessageField_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedMessageField(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> values) {

+        PrepareBuilder();

         result.repeatedMessageField_.Add(values);

         return this;

       }

       public Builder ClearRepeatedMessageField() {

+        PrepareBuilder();

         result.repeatedMessageField_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedStringPieceFieldList {

-        get { return result.repeatedStringPieceField_; }

+        get { return PrepareBuilder().repeatedStringPieceField_; }

       }

       public int RepeatedStringPieceFieldCount {

         get { return result.RepeatedStringPieceFieldCount; }

@@ -13069,25 +14173,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedStringPieceField(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedStringPieceField_[index] = value;

         return this;

       }

       public Builder AddRepeatedStringPieceField(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedStringPieceField_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedStringPieceField(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedStringPieceField_.Add(values);

         return this;

       }

       public Builder ClearRepeatedStringPieceField() {

+        PrepareBuilder();

         result.repeatedStringPieceField_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedCordFieldList {

-        get { return result.repeatedCordField_; }

+        get { return PrepareBuilder().repeatedCordField_; }

       }

       public int RepeatedCordFieldCount {

         get { return result.RepeatedCordFieldCount; }

@@ -13097,19 +14205,23 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedCordField(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedCordField_[index] = value;

         return this;

       }

       public Builder AddRepeatedCordField(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedCordField_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedCordField(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedCordField_.Add(values);

         return this;

       }

       public Builder ClearRepeatedCordField() {

+        PrepareBuilder();

         result.repeatedCordField_.Clear();

         return this;

       }

@@ -13259,7 +14371,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestFieldOrderings prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -13269,21 +14381,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestFieldOrderings();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestFieldOrderings cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestFieldOrderings result;

+      

+      private TestFieldOrderings PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestFieldOrderings original = result;

+          result = new TestFieldOrderings();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestFieldOrderings result = new TestFieldOrderings();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestFieldOrderings MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestFieldOrderings();

+        result = DefaultInstance ?? new TestFieldOrderings();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -13295,12 +14434,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestFieldOrderings BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestFieldOrderings returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -13314,6 +14452,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestFieldOrderings other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestFieldOrderings.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasMyString) {

           MyString = other.MyString;

         }

@@ -13333,6 +14472,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -13397,11 +14537,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetMyString(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasMyString = true;

         result.myString_ = value;

         return this;

       }

       public Builder ClearMyString() {

+        PrepareBuilder();

         result.hasMyString = false;

         result.myString_ = "";

         return this;

@@ -13415,11 +14557,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetMyInt(value); }

       }

       public Builder SetMyInt(long value) {

+        PrepareBuilder();

         result.hasMyInt = true;

         result.myInt_ = value;

         return this;

       }

       public Builder ClearMyInt() {

+        PrepareBuilder();

         result.hasMyInt = false;

         result.myInt_ = 0L;

         return this;

@@ -13433,11 +14577,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetMyFloat(value); }

       }

       public Builder SetMyFloat(float value) {

+        PrepareBuilder();

         result.hasMyFloat = true;

         result.myFloat_ = value;

         return this;

       }

       public Builder ClearMyFloat() {

+        PrepareBuilder();

         result.hasMyFloat = false;

         result.myFloat_ = 0F;

         return this;

@@ -13841,7 +14987,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestExtremeDefaultValues prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -13851,21 +14997,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestExtremeDefaultValues();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestExtremeDefaultValues cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestExtremeDefaultValues result;

       

-      TestExtremeDefaultValues result = new TestExtremeDefaultValues();

+      private TestExtremeDefaultValues PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestExtremeDefaultValues original = result;

+          result = new TestExtremeDefaultValues();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestExtremeDefaultValues MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestExtremeDefaultValues();

+        result = DefaultInstance ?? new TestExtremeDefaultValues();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -13877,12 +15050,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestExtremeDefaultValues BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestExtremeDefaultValues returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -13896,6 +15068,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestExtremeDefaultValues other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestExtremeDefaultValues.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasEscapedBytes) {

           EscapedBytes = other.EscapedBytes;

         }

@@ -13962,6 +15135,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -14090,11 +15264,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetEscapedBytes(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasEscapedBytes = true;

         result.escapedBytes_ = value;

         return this;

       }

       public Builder ClearEscapedBytes() {

+        PrepareBuilder();

         result.hasEscapedBytes = false;

         result.escapedBytes_ = (pb::ByteString) global::Google.ProtocolBuffers.TestProtos.TestExtremeDefaultValues.Descriptor.Fields[0].DefaultValue;

         return this;

@@ -14110,11 +15286,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetLargeUint32(uint value) {

+        PrepareBuilder();

         result.hasLargeUint32 = true;

         result.largeUint32_ = value;

         return this;

       }

       public Builder ClearLargeUint32() {

+        PrepareBuilder();

         result.hasLargeUint32 = false;

         result.largeUint32_ = 4294967295;

         return this;

@@ -14130,11 +15308,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetLargeUint64(ulong value) {

+        PrepareBuilder();

         result.hasLargeUint64 = true;

         result.largeUint64_ = value;

         return this;

       }

       public Builder ClearLargeUint64() {

+        PrepareBuilder();

         result.hasLargeUint64 = false;

         result.largeUint64_ = 18446744073709551615UL;

         return this;

@@ -14148,11 +15328,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetSmallInt32(value); }

       }

       public Builder SetSmallInt32(int value) {

+        PrepareBuilder();

         result.hasSmallInt32 = true;

         result.smallInt32_ = value;

         return this;

       }

       public Builder ClearSmallInt32() {

+        PrepareBuilder();

         result.hasSmallInt32 = false;

         result.smallInt32_ = -2147483647;

         return this;

@@ -14166,11 +15348,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetSmallInt64(value); }

       }

       public Builder SetSmallInt64(long value) {

+        PrepareBuilder();

         result.hasSmallInt64 = true;

         result.smallInt64_ = value;

         return this;

       }

       public Builder ClearSmallInt64() {

+        PrepareBuilder();

         result.hasSmallInt64 = false;

         result.smallInt64_ = -9223372036854775807L;

         return this;

@@ -14185,11 +15369,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetUtf8String(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasUtf8String = true;

         result.utf8String_ = value;

         return this;

       }

       public Builder ClearUtf8String() {

+        PrepareBuilder();

         result.hasUtf8String = false;

         result.utf8String_ = (string) global::Google.ProtocolBuffers.TestProtos.TestExtremeDefaultValues.Descriptor.Fields[5].DefaultValue;

         return this;

@@ -14203,11 +15389,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetZeroFloat(value); }

       }

       public Builder SetZeroFloat(float value) {

+        PrepareBuilder();

         result.hasZeroFloat = true;

         result.zeroFloat_ = value;

         return this;

       }

       public Builder ClearZeroFloat() {

+        PrepareBuilder();

         result.hasZeroFloat = false;

         result.zeroFloat_ = 0F;

         return this;

@@ -14221,11 +15409,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOneFloat(value); }

       }

       public Builder SetOneFloat(float value) {

+        PrepareBuilder();

         result.hasOneFloat = true;

         result.oneFloat_ = value;

         return this;

       }

       public Builder ClearOneFloat() {

+        PrepareBuilder();

         result.hasOneFloat = false;

         result.oneFloat_ = 1F;

         return this;

@@ -14239,11 +15429,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetSmallFloat(value); }

       }

       public Builder SetSmallFloat(float value) {

+        PrepareBuilder();

         result.hasSmallFloat = true;

         result.smallFloat_ = value;

         return this;

       }

       public Builder ClearSmallFloat() {

+        PrepareBuilder();

         result.hasSmallFloat = false;

         result.smallFloat_ = 1.5F;

         return this;

@@ -14257,11 +15449,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetNegativeOneFloat(value); }

       }

       public Builder SetNegativeOneFloat(float value) {

+        PrepareBuilder();

         result.hasNegativeOneFloat = true;

         result.negativeOneFloat_ = value;

         return this;

       }

       public Builder ClearNegativeOneFloat() {

+        PrepareBuilder();

         result.hasNegativeOneFloat = false;

         result.negativeOneFloat_ = -1F;

         return this;

@@ -14275,11 +15469,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetNegativeFloat(value); }

       }

       public Builder SetNegativeFloat(float value) {

+        PrepareBuilder();

         result.hasNegativeFloat = true;

         result.negativeFloat_ = value;

         return this;

       }

       public Builder ClearNegativeFloat() {

+        PrepareBuilder();

         result.hasNegativeFloat = false;

         result.negativeFloat_ = -1.5F;

         return this;

@@ -14293,11 +15489,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetLargeFloat(value); }

       }

       public Builder SetLargeFloat(float value) {

+        PrepareBuilder();

         result.hasLargeFloat = true;

         result.largeFloat_ = value;

         return this;

       }

       public Builder ClearLargeFloat() {

+        PrepareBuilder();

         result.hasLargeFloat = false;

         result.largeFloat_ = 2E+08F;

         return this;

@@ -14311,11 +15509,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetSmallNegativeFloat(value); }

       }

       public Builder SetSmallNegativeFloat(float value) {

+        PrepareBuilder();

         result.hasSmallNegativeFloat = true;

         result.smallNegativeFloat_ = value;

         return this;

       }

       public Builder ClearSmallNegativeFloat() {

+        PrepareBuilder();

         result.hasSmallNegativeFloat = false;

         result.smallNegativeFloat_ = -8E-28F;

         return this;

@@ -14329,11 +15529,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetInfDouble(value); }

       }

       public Builder SetInfDouble(double value) {

+        PrepareBuilder();

         result.hasInfDouble = true;

         result.infDouble_ = value;

         return this;

       }

       public Builder ClearInfDouble() {

+        PrepareBuilder();

         result.hasInfDouble = false;

         result.infDouble_ = double.PositiveInfinity;

         return this;

@@ -14347,11 +15549,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetNegInfDouble(value); }

       }

       public Builder SetNegInfDouble(double value) {

+        PrepareBuilder();

         result.hasNegInfDouble = true;

         result.negInfDouble_ = value;

         return this;

       }

       public Builder ClearNegInfDouble() {

+        PrepareBuilder();

         result.hasNegInfDouble = false;

         result.negInfDouble_ = double.NegativeInfinity;

         return this;

@@ -14365,11 +15569,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetNanDouble(value); }

       }

       public Builder SetNanDouble(double value) {

+        PrepareBuilder();

         result.hasNanDouble = true;

         result.nanDouble_ = value;

         return this;

       }

       public Builder ClearNanDouble() {

+        PrepareBuilder();

         result.hasNanDouble = false;

         result.nanDouble_ = double.NaN;

         return this;

@@ -14383,11 +15589,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetInfFloat(value); }

       }

       public Builder SetInfFloat(float value) {

+        PrepareBuilder();

         result.hasInfFloat = true;

         result.infFloat_ = value;

         return this;

       }

       public Builder ClearInfFloat() {

+        PrepareBuilder();

         result.hasInfFloat = false;

         result.infFloat_ = float.PositiveInfinity;

         return this;

@@ -14401,11 +15609,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetNegInfFloat(value); }

       }

       public Builder SetNegInfFloat(float value) {

+        PrepareBuilder();

         result.hasNegInfFloat = true;

         result.negInfFloat_ = value;

         return this;

       }

       public Builder ClearNegInfFloat() {

+        PrepareBuilder();

         result.hasNegInfFloat = false;

         result.negInfFloat_ = float.NegativeInfinity;

         return this;

@@ -14419,11 +15629,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetNanFloat(value); }

       }

       public Builder SetNanFloat(float value) {

+        PrepareBuilder();

         result.hasNanFloat = true;

         result.nanFloat_ = value;

         return this;

       }

       public Builder ClearNanFloat() {

+        PrepareBuilder();

         result.hasNanFloat = false;

         result.nanFloat_ = float.NaN;

         return this;

@@ -14537,7 +15749,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(OneString prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -14547,21 +15759,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new OneString();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(OneString cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      OneString result = new OneString();

+      bool builderIsReadOnly;

+      OneString result;

+      

+      private OneString PrepareBuilder() {

+        if (builderIsReadOnly) {

+          OneString original = result;

+          result = new OneString();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override OneString MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new OneString();

+        result = DefaultInstance ?? new OneString();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -14573,12 +15812,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override OneString BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        OneString returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -14592,6 +15830,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(OneString other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.OneString.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasData) {

           Data = other.Data;

         }

@@ -14604,6 +15843,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -14660,11 +15900,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetData(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasData = true;

         result.data_ = value;

         return this;

       }

       public Builder ClearData() {

+        PrepareBuilder();

         result.hasData = false;

         result.data_ = "";

         return this;

@@ -14778,7 +16020,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(OneBytes prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -14788,21 +16030,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new OneBytes();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(OneBytes cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      OneBytes result = new OneBytes();

+      bool builderIsReadOnly;

+      OneBytes result;

+      

+      private OneBytes PrepareBuilder() {

+        if (builderIsReadOnly) {

+          OneBytes original = result;

+          result = new OneBytes();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override OneBytes MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new OneBytes();

+        result = DefaultInstance ?? new OneBytes();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -14814,12 +16083,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override OneBytes BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        OneBytes returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -14833,6 +16101,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(OneBytes other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.OneBytes.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasData) {

           Data = other.Data;

         }

@@ -14845,6 +16114,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -14901,11 +16171,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetData(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasData = true;

         result.data_ = value;

         return this;

       }

       public Builder ClearData() {

+        PrepareBuilder();

         result.hasData = false;

         result.data_ = pb::ByteString.Empty;

         return this;

@@ -15376,7 +16648,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestPackedTypes prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -15386,21 +16658,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestPackedTypes();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestPackedTypes cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestPackedTypes result = new TestPackedTypes();

+      bool builderIsReadOnly;

+      TestPackedTypes result;

+      

+      private TestPackedTypes PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestPackedTypes original = result;

+          result = new TestPackedTypes();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestPackedTypes MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestPackedTypes();

+        result = DefaultInstance ?? new TestPackedTypes();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -15412,8 +16711,8 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestPackedTypes BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.packedInt32_.MakeReadOnly();

         result.packedInt64_.MakeReadOnly();

@@ -15429,9 +16728,8 @@ namespace Google.ProtocolBuffers.TestProtos {
         result.packedDouble_.MakeReadOnly();

         result.packedBool_.MakeReadOnly();

         result.packedEnum_.MakeReadOnly();

-        TestPackedTypes returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -15445,6 +16743,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestPackedTypes other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestPackedTypes.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.packedInt32_.Count != 0) {

           result.packedInt32_.Add(other.packedInt32_);

         }

@@ -15496,6 +16795,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -15619,7 +16919,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       

       public pbc::IPopsicleList<int> PackedInt32List {

-        get { return result.packedInt32_; }

+        get { return PrepareBuilder().packedInt32_; }

       }

       public int PackedInt32Count {

         get { return result.PackedInt32Count; }

@@ -15628,24 +16928,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedInt32(index);

       }

       public Builder SetPackedInt32(int index, int value) {

+        PrepareBuilder();

         result.packedInt32_[index] = value;

         return this;

       }

       public Builder AddPackedInt32(int value) {

+        PrepareBuilder();

         result.packedInt32_.Add(value);

         return this;

       }

       public Builder AddRangePackedInt32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.packedInt32_.Add(values);

         return this;

       }

       public Builder ClearPackedInt32() {

+        PrepareBuilder();

         result.packedInt32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> PackedInt64List {

-        get { return result.packedInt64_; }

+        get { return PrepareBuilder().packedInt64_; }

       }

       public int PackedInt64Count {

         get { return result.PackedInt64Count; }

@@ -15654,25 +16958,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedInt64(index);

       }

       public Builder SetPackedInt64(int index, long value) {

+        PrepareBuilder();

         result.packedInt64_[index] = value;

         return this;

       }

       public Builder AddPackedInt64(long value) {

+        PrepareBuilder();

         result.packedInt64_.Add(value);

         return this;

       }

       public Builder AddRangePackedInt64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.packedInt64_.Add(values);

         return this;

       }

       public Builder ClearPackedInt64() {

+        PrepareBuilder();

         result.packedInt64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> PackedUint32List {

-        get { return result.packedUint32_; }

+        get { return PrepareBuilder().packedUint32_; }

       }

       public int PackedUint32Count {

         get { return result.PackedUint32Count; }

@@ -15683,27 +16991,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetPackedUint32(int index, uint value) {

+        PrepareBuilder();

         result.packedUint32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddPackedUint32(uint value) {

+        PrepareBuilder();

         result.packedUint32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangePackedUint32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.packedUint32_.Add(values);

         return this;

       }

       public Builder ClearPackedUint32() {

+        PrepareBuilder();

         result.packedUint32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> PackedUint64List {

-        get { return result.packedUint64_; }

+        get { return PrepareBuilder().packedUint64_; }

       }

       public int PackedUint64Count {

         get { return result.PackedUint64Count; }

@@ -15714,26 +17026,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetPackedUint64(int index, ulong value) {

+        PrepareBuilder();

         result.packedUint64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddPackedUint64(ulong value) {

+        PrepareBuilder();

         result.packedUint64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangePackedUint64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.packedUint64_.Add(values);

         return this;

       }

       public Builder ClearPackedUint64() {

+        PrepareBuilder();

         result.packedUint64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> PackedSint32List {

-        get { return result.packedSint32_; }

+        get { return PrepareBuilder().packedSint32_; }

       }

       public int PackedSint32Count {

         get { return result.PackedSint32Count; }

@@ -15742,24 +17058,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedSint32(index);

       }

       public Builder SetPackedSint32(int index, int value) {

+        PrepareBuilder();

         result.packedSint32_[index] = value;

         return this;

       }

       public Builder AddPackedSint32(int value) {

+        PrepareBuilder();

         result.packedSint32_.Add(value);

         return this;

       }

       public Builder AddRangePackedSint32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.packedSint32_.Add(values);

         return this;

       }

       public Builder ClearPackedSint32() {

+        PrepareBuilder();

         result.packedSint32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> PackedSint64List {

-        get { return result.packedSint64_; }

+        get { return PrepareBuilder().packedSint64_; }

       }

       public int PackedSint64Count {

         get { return result.PackedSint64Count; }

@@ -15768,25 +17088,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedSint64(index);

       }

       public Builder SetPackedSint64(int index, long value) {

+        PrepareBuilder();

         result.packedSint64_[index] = value;

         return this;

       }

       public Builder AddPackedSint64(long value) {

+        PrepareBuilder();

         result.packedSint64_.Add(value);

         return this;

       }

       public Builder AddRangePackedSint64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.packedSint64_.Add(values);

         return this;

       }

       public Builder ClearPackedSint64() {

+        PrepareBuilder();

         result.packedSint64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> PackedFixed32List {

-        get { return result.packedFixed32_; }

+        get { return PrepareBuilder().packedFixed32_; }

       }

       public int PackedFixed32Count {

         get { return result.PackedFixed32Count; }

@@ -15797,27 +17121,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetPackedFixed32(int index, uint value) {

+        PrepareBuilder();

         result.packedFixed32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddPackedFixed32(uint value) {

+        PrepareBuilder();

         result.packedFixed32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangePackedFixed32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.packedFixed32_.Add(values);

         return this;

       }

       public Builder ClearPackedFixed32() {

+        PrepareBuilder();

         result.packedFixed32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> PackedFixed64List {

-        get { return result.packedFixed64_; }

+        get { return PrepareBuilder().packedFixed64_; }

       }

       public int PackedFixed64Count {

         get { return result.PackedFixed64Count; }

@@ -15828,26 +17156,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetPackedFixed64(int index, ulong value) {

+        PrepareBuilder();

         result.packedFixed64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddPackedFixed64(ulong value) {

+        PrepareBuilder();

         result.packedFixed64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangePackedFixed64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.packedFixed64_.Add(values);

         return this;

       }

       public Builder ClearPackedFixed64() {

+        PrepareBuilder();

         result.packedFixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> PackedSfixed32List {

-        get { return result.packedSfixed32_; }

+        get { return PrepareBuilder().packedSfixed32_; }

       }

       public int PackedSfixed32Count {

         get { return result.PackedSfixed32Count; }

@@ -15856,24 +17188,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedSfixed32(index);

       }

       public Builder SetPackedSfixed32(int index, int value) {

+        PrepareBuilder();

         result.packedSfixed32_[index] = value;

         return this;

       }

       public Builder AddPackedSfixed32(int value) {

+        PrepareBuilder();

         result.packedSfixed32_.Add(value);

         return this;

       }

       public Builder AddRangePackedSfixed32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.packedSfixed32_.Add(values);

         return this;

       }

       public Builder ClearPackedSfixed32() {

+        PrepareBuilder();

         result.packedSfixed32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> PackedSfixed64List {

-        get { return result.packedSfixed64_; }

+        get { return PrepareBuilder().packedSfixed64_; }

       }

       public int PackedSfixed64Count {

         get { return result.PackedSfixed64Count; }

@@ -15882,24 +17218,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedSfixed64(index);

       }

       public Builder SetPackedSfixed64(int index, long value) {

+        PrepareBuilder();

         result.packedSfixed64_[index] = value;

         return this;

       }

       public Builder AddPackedSfixed64(long value) {

+        PrepareBuilder();

         result.packedSfixed64_.Add(value);

         return this;

       }

       public Builder AddRangePackedSfixed64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.packedSfixed64_.Add(values);

         return this;

       }

       public Builder ClearPackedSfixed64() {

+        PrepareBuilder();

         result.packedSfixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<float> PackedFloatList {

-        get { return result.packedFloat_; }

+        get { return PrepareBuilder().packedFloat_; }

       }

       public int PackedFloatCount {

         get { return result.PackedFloatCount; }

@@ -15908,24 +17248,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedFloat(index);

       }

       public Builder SetPackedFloat(int index, float value) {

+        PrepareBuilder();

         result.packedFloat_[index] = value;

         return this;

       }

       public Builder AddPackedFloat(float value) {

+        PrepareBuilder();

         result.packedFloat_.Add(value);

         return this;

       }

       public Builder AddRangePackedFloat(scg::IEnumerable<float> values) {

+        PrepareBuilder();

         result.packedFloat_.Add(values);

         return this;

       }

       public Builder ClearPackedFloat() {

+        PrepareBuilder();

         result.packedFloat_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<double> PackedDoubleList {

-        get { return result.packedDouble_; }

+        get { return PrepareBuilder().packedDouble_; }

       }

       public int PackedDoubleCount {

         get { return result.PackedDoubleCount; }

@@ -15934,24 +17278,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedDouble(index);

       }

       public Builder SetPackedDouble(int index, double value) {

+        PrepareBuilder();

         result.packedDouble_[index] = value;

         return this;

       }

       public Builder AddPackedDouble(double value) {

+        PrepareBuilder();

         result.packedDouble_.Add(value);

         return this;

       }

       public Builder AddRangePackedDouble(scg::IEnumerable<double> values) {

+        PrepareBuilder();

         result.packedDouble_.Add(values);

         return this;

       }

       public Builder ClearPackedDouble() {

+        PrepareBuilder();

         result.packedDouble_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<bool> PackedBoolList {

-        get { return result.packedBool_; }

+        get { return PrepareBuilder().packedBool_; }

       }

       public int PackedBoolCount {

         get { return result.PackedBoolCount; }

@@ -15960,24 +17308,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedBool(index);

       }

       public Builder SetPackedBool(int index, bool value) {

+        PrepareBuilder();

         result.packedBool_[index] = value;

         return this;

       }

       public Builder AddPackedBool(bool value) {

+        PrepareBuilder();

         result.packedBool_.Add(value);

         return this;

       }

       public Builder AddRangePackedBool(scg::IEnumerable<bool> values) {

+        PrepareBuilder();

         result.packedBool_.Add(values);

         return this;

       }

       public Builder ClearPackedBool() {

+        PrepareBuilder();

         result.packedBool_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> PackedEnumList {

-        get { return result.packedEnum_; }

+        get { return PrepareBuilder().packedEnum_; }

       }

       public int PackedEnumCount {

         get { return result.PackedEnumCount; }

@@ -15986,18 +17338,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedEnum(index);

       }

       public Builder SetPackedEnum(int index, global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.packedEnum_[index] = value;

         return this;

       }

       public Builder AddPackedEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.packedEnum_.Add(value);

         return this;

       }

       public Builder AddRangePackedEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> values) {

+        PrepareBuilder();

         result.packedEnum_.Add(values);

         return this;

       }

       public Builder ClearPackedEnum() {

+        PrepareBuilder();

         result.packedEnum_.Clear();

         return this;

       }

@@ -16412,7 +17768,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestUnpackedTypes prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -16422,21 +17778,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestUnpackedTypes();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestUnpackedTypes cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestUnpackedTypes result;

+      

+      private TestUnpackedTypes PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestUnpackedTypes original = result;

+          result = new TestUnpackedTypes();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestUnpackedTypes result = new TestUnpackedTypes();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestUnpackedTypes MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestUnpackedTypes();

+        result = DefaultInstance ?? new TestUnpackedTypes();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -16448,8 +17831,8 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestUnpackedTypes BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.unpackedInt32_.MakeReadOnly();

         result.unpackedInt64_.MakeReadOnly();

@@ -16465,9 +17848,8 @@ namespace Google.ProtocolBuffers.TestProtos {
         result.unpackedDouble_.MakeReadOnly();

         result.unpackedBool_.MakeReadOnly();

         result.unpackedEnum_.MakeReadOnly();

-        TestUnpackedTypes returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -16481,6 +17863,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestUnpackedTypes other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestUnpackedTypes.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.unpackedInt32_.Count != 0) {

           result.unpackedInt32_.Add(other.unpackedInt32_);

         }

@@ -16532,6 +17915,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -16655,7 +18039,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       

       public pbc::IPopsicleList<int> UnpackedInt32List {

-        get { return result.unpackedInt32_; }

+        get { return PrepareBuilder().unpackedInt32_; }

       }

       public int UnpackedInt32Count {

         get { return result.UnpackedInt32Count; }

@@ -16664,24 +18048,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedInt32(index);

       }

       public Builder SetUnpackedInt32(int index, int value) {

+        PrepareBuilder();

         result.unpackedInt32_[index] = value;

         return this;

       }

       public Builder AddUnpackedInt32(int value) {

+        PrepareBuilder();

         result.unpackedInt32_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedInt32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.unpackedInt32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedInt32() {

+        PrepareBuilder();

         result.unpackedInt32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> UnpackedInt64List {

-        get { return result.unpackedInt64_; }

+        get { return PrepareBuilder().unpackedInt64_; }

       }

       public int UnpackedInt64Count {

         get { return result.UnpackedInt64Count; }

@@ -16690,25 +18078,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedInt64(index);

       }

       public Builder SetUnpackedInt64(int index, long value) {

+        PrepareBuilder();

         result.unpackedInt64_[index] = value;

         return this;

       }

       public Builder AddUnpackedInt64(long value) {

+        PrepareBuilder();

         result.unpackedInt64_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedInt64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.unpackedInt64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedInt64() {

+        PrepareBuilder();

         result.unpackedInt64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> UnpackedUint32List {

-        get { return result.unpackedUint32_; }

+        get { return PrepareBuilder().unpackedUint32_; }

       }

       public int UnpackedUint32Count {

         get { return result.UnpackedUint32Count; }

@@ -16719,27 +18111,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetUnpackedUint32(int index, uint value) {

+        PrepareBuilder();

         result.unpackedUint32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddUnpackedUint32(uint value) {

+        PrepareBuilder();

         result.unpackedUint32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeUnpackedUint32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.unpackedUint32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedUint32() {

+        PrepareBuilder();

         result.unpackedUint32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> UnpackedUint64List {

-        get { return result.unpackedUint64_; }

+        get { return PrepareBuilder().unpackedUint64_; }

       }

       public int UnpackedUint64Count {

         get { return result.UnpackedUint64Count; }

@@ -16750,26 +18146,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetUnpackedUint64(int index, ulong value) {

+        PrepareBuilder();

         result.unpackedUint64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddUnpackedUint64(ulong value) {

+        PrepareBuilder();

         result.unpackedUint64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeUnpackedUint64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.unpackedUint64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedUint64() {

+        PrepareBuilder();

         result.unpackedUint64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> UnpackedSint32List {

-        get { return result.unpackedSint32_; }

+        get { return PrepareBuilder().unpackedSint32_; }

       }

       public int UnpackedSint32Count {

         get { return result.UnpackedSint32Count; }

@@ -16778,24 +18178,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedSint32(index);

       }

       public Builder SetUnpackedSint32(int index, int value) {

+        PrepareBuilder();

         result.unpackedSint32_[index] = value;

         return this;

       }

       public Builder AddUnpackedSint32(int value) {

+        PrepareBuilder();

         result.unpackedSint32_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedSint32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.unpackedSint32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedSint32() {

+        PrepareBuilder();

         result.unpackedSint32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> UnpackedSint64List {

-        get { return result.unpackedSint64_; }

+        get { return PrepareBuilder().unpackedSint64_; }

       }

       public int UnpackedSint64Count {

         get { return result.UnpackedSint64Count; }

@@ -16804,25 +18208,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedSint64(index);

       }

       public Builder SetUnpackedSint64(int index, long value) {

+        PrepareBuilder();

         result.unpackedSint64_[index] = value;

         return this;

       }

       public Builder AddUnpackedSint64(long value) {

+        PrepareBuilder();

         result.unpackedSint64_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedSint64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.unpackedSint64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedSint64() {

+        PrepareBuilder();

         result.unpackedSint64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> UnpackedFixed32List {

-        get { return result.unpackedFixed32_; }

+        get { return PrepareBuilder().unpackedFixed32_; }

       }

       public int UnpackedFixed32Count {

         get { return result.UnpackedFixed32Count; }

@@ -16833,27 +18241,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetUnpackedFixed32(int index, uint value) {

+        PrepareBuilder();

         result.unpackedFixed32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddUnpackedFixed32(uint value) {

+        PrepareBuilder();

         result.unpackedFixed32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeUnpackedFixed32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.unpackedFixed32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedFixed32() {

+        PrepareBuilder();

         result.unpackedFixed32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> UnpackedFixed64List {

-        get { return result.unpackedFixed64_; }

+        get { return PrepareBuilder().unpackedFixed64_; }

       }

       public int UnpackedFixed64Count {

         get { return result.UnpackedFixed64Count; }

@@ -16864,26 +18276,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetUnpackedFixed64(int index, ulong value) {

+        PrepareBuilder();

         result.unpackedFixed64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddUnpackedFixed64(ulong value) {

+        PrepareBuilder();

         result.unpackedFixed64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeUnpackedFixed64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.unpackedFixed64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedFixed64() {

+        PrepareBuilder();

         result.unpackedFixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> UnpackedSfixed32List {

-        get { return result.unpackedSfixed32_; }

+        get { return PrepareBuilder().unpackedSfixed32_; }

       }

       public int UnpackedSfixed32Count {

         get { return result.UnpackedSfixed32Count; }

@@ -16892,24 +18308,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedSfixed32(index);

       }

       public Builder SetUnpackedSfixed32(int index, int value) {

+        PrepareBuilder();

         result.unpackedSfixed32_[index] = value;

         return this;

       }

       public Builder AddUnpackedSfixed32(int value) {

+        PrepareBuilder();

         result.unpackedSfixed32_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedSfixed32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.unpackedSfixed32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedSfixed32() {

+        PrepareBuilder();

         result.unpackedSfixed32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> UnpackedSfixed64List {

-        get { return result.unpackedSfixed64_; }

+        get { return PrepareBuilder().unpackedSfixed64_; }

       }

       public int UnpackedSfixed64Count {

         get { return result.UnpackedSfixed64Count; }

@@ -16918,24 +18338,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedSfixed64(index);

       }

       public Builder SetUnpackedSfixed64(int index, long value) {

+        PrepareBuilder();

         result.unpackedSfixed64_[index] = value;

         return this;

       }

       public Builder AddUnpackedSfixed64(long value) {

+        PrepareBuilder();

         result.unpackedSfixed64_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedSfixed64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.unpackedSfixed64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedSfixed64() {

+        PrepareBuilder();

         result.unpackedSfixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<float> UnpackedFloatList {

-        get { return result.unpackedFloat_; }

+        get { return PrepareBuilder().unpackedFloat_; }

       }

       public int UnpackedFloatCount {

         get { return result.UnpackedFloatCount; }

@@ -16944,24 +18368,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedFloat(index);

       }

       public Builder SetUnpackedFloat(int index, float value) {

+        PrepareBuilder();

         result.unpackedFloat_[index] = value;

         return this;

       }

       public Builder AddUnpackedFloat(float value) {

+        PrepareBuilder();

         result.unpackedFloat_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedFloat(scg::IEnumerable<float> values) {

+        PrepareBuilder();

         result.unpackedFloat_.Add(values);

         return this;

       }

       public Builder ClearUnpackedFloat() {

+        PrepareBuilder();

         result.unpackedFloat_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<double> UnpackedDoubleList {

-        get { return result.unpackedDouble_; }

+        get { return PrepareBuilder().unpackedDouble_; }

       }

       public int UnpackedDoubleCount {

         get { return result.UnpackedDoubleCount; }

@@ -16970,24 +18398,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedDouble(index);

       }

       public Builder SetUnpackedDouble(int index, double value) {

+        PrepareBuilder();

         result.unpackedDouble_[index] = value;

         return this;

       }

       public Builder AddUnpackedDouble(double value) {

+        PrepareBuilder();

         result.unpackedDouble_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedDouble(scg::IEnumerable<double> values) {

+        PrepareBuilder();

         result.unpackedDouble_.Add(values);

         return this;

       }

       public Builder ClearUnpackedDouble() {

+        PrepareBuilder();

         result.unpackedDouble_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<bool> UnpackedBoolList {

-        get { return result.unpackedBool_; }

+        get { return PrepareBuilder().unpackedBool_; }

       }

       public int UnpackedBoolCount {

         get { return result.UnpackedBoolCount; }

@@ -16996,24 +18428,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedBool(index);

       }

       public Builder SetUnpackedBool(int index, bool value) {

+        PrepareBuilder();

         result.unpackedBool_[index] = value;

         return this;

       }

       public Builder AddUnpackedBool(bool value) {

+        PrepareBuilder();

         result.unpackedBool_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedBool(scg::IEnumerable<bool> values) {

+        PrepareBuilder();

         result.unpackedBool_.Add(values);

         return this;

       }

       public Builder ClearUnpackedBool() {

+        PrepareBuilder();

         result.unpackedBool_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> UnpackedEnumList {

-        get { return result.unpackedEnum_; }

+        get { return PrepareBuilder().unpackedEnum_; }

       }

       public int UnpackedEnumCount {

         get { return result.UnpackedEnumCount; }

@@ -17022,18 +18458,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedEnum(index);

       }

       public Builder SetUnpackedEnum(int index, global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.unpackedEnum_[index] = value;

         return this;

       }

       public Builder AddUnpackedEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.unpackedEnum_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> values) {

+        PrepareBuilder();

         result.unpackedEnum_.Add(values);

         return this;

       }

       public Builder ClearUnpackedEnum() {

+        PrepareBuilder();

         result.unpackedEnum_.Clear();

         return this;

       }

@@ -17134,7 +18574,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestPackedExtensions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -17144,21 +18584,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestPackedExtensions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestPackedExtensions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestPackedExtensions result;

+      

+      private TestPackedExtensions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestPackedExtensions original = result;

+          result = new TestPackedExtensions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestPackedExtensions result = new TestPackedExtensions();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestPackedExtensions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestPackedExtensions();

+        result = DefaultInstance ?? new TestPackedExtensions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -17170,12 +18637,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestPackedExtensions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestPackedExtensions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -17189,6 +18655,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestPackedExtensions other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestPackedExtensions.DefaultInstance) return this;

+        PrepareBuilder();

           this.MergeExtensionFields(other);

         this.MergeUnknownFields(other.UnknownFields);

         return this;

@@ -17199,6 +18666,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -17338,7 +18806,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestUnpackedExtensions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -17348,21 +18816,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestUnpackedExtensions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestUnpackedExtensions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestUnpackedExtensions result;

+      

+      private TestUnpackedExtensions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestUnpackedExtensions original = result;

+          result = new TestUnpackedExtensions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestUnpackedExtensions result = new TestUnpackedExtensions();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestUnpackedExtensions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestUnpackedExtensions();

+        result = DefaultInstance ?? new TestUnpackedExtensions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -17374,12 +18869,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestUnpackedExtensions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestUnpackedExtensions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -17393,6 +18887,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestUnpackedExtensions other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestUnpackedExtensions.DefaultInstance) return this;

+        PrepareBuilder();

           this.MergeExtensionFields(other);

         this.MergeUnknownFields(other.UnknownFields);

         return this;

@@ -17403,6 +18898,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -17595,7 +19091,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(DynamicMessageType prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -17605,21 +19101,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new DynamicMessageType();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(DynamicMessageType cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          DynamicMessageType result;

           

-          DynamicMessageType result = new DynamicMessageType();

+          private DynamicMessageType PrepareBuilder() {

+            if (builderIsReadOnly) {

+              DynamicMessageType original = result;

+              result = new DynamicMessageType();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override DynamicMessageType MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new DynamicMessageType();

+            result = DefaultInstance ?? new DynamicMessageType();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -17631,12 +19154,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override DynamicMessageType BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            DynamicMessageType returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -17650,6 +19172,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(DynamicMessageType other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasDynamicField) {

               DynamicField = other.DynamicField;

             }

@@ -17662,6 +19185,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -17717,11 +19241,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetDynamicField(value); }

           }

           public Builder SetDynamicField(int value) {

+            PrepareBuilder();

             result.hasDynamicField = true;

             result.dynamicField_ = value;

             return this;

           }

           public Builder ClearDynamicField() {

+            PrepareBuilder();

             result.hasDynamicField = false;

             result.dynamicField_ = 0;

             return this;

@@ -17925,7 +19451,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestDynamicExtensions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -17935,21 +19461,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestDynamicExtensions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestDynamicExtensions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestDynamicExtensions result = new TestDynamicExtensions();

+      bool builderIsReadOnly;

+      TestDynamicExtensions result;

+      

+      private TestDynamicExtensions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestDynamicExtensions original = result;

+          result = new TestDynamicExtensions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestDynamicExtensions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestDynamicExtensions();

+        result = DefaultInstance ?? new TestDynamicExtensions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -17961,14 +19514,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestDynamicExtensions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.repeatedExtension_.MakeReadOnly();

         result.packedExtension_.MakeReadOnly();

-        TestDynamicExtensions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -17982,6 +19534,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestDynamicExtensions other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasScalarExtension) {

           ScalarExtension = other.ScalarExtension;

         }

@@ -18012,6 +19565,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -18120,11 +19674,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetScalarExtension(uint value) {

+        PrepareBuilder();

         result.hasScalarExtension = true;

         result.scalarExtension_ = value;

         return this;

       }

       public Builder ClearScalarExtension() {

+        PrepareBuilder();

         result.hasScalarExtension = false;

         result.scalarExtension_ = 0;

         return this;

@@ -18138,11 +19694,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetEnumExtension(value); }

       }

       public Builder SetEnumExtension(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.hasEnumExtension = true;

         result.enumExtension_ = value;

         return this;

       }

       public Builder ClearEnumExtension() {

+        PrepareBuilder();

         result.hasEnumExtension = false;

         result.enumExtension_ = global::Google.ProtocolBuffers.TestProtos.ForeignEnum.FOREIGN_FOO;

         return this;

@@ -18156,11 +19714,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDynamicEnumExtension(value); }

       }

       public Builder SetDynamicEnumExtension(global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicEnumType value) {

+        PrepareBuilder();

         result.hasDynamicEnumExtension = true;

         result.dynamicEnumExtension_ = value;

         return this;

       }

       public Builder ClearDynamicEnumExtension() {

+        PrepareBuilder();

         result.hasDynamicEnumExtension = false;

         result.dynamicEnumExtension_ = global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicEnumType.DYNAMIC_FOO;

         return this;

@@ -18175,18 +19735,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetMessageExtension(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasMessageExtension = true;

         result.messageExtension_ = value;

         return this;

       }

       public Builder SetMessageExtension(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasMessageExtension = true;

         result.messageExtension_ = builderForValue.Build();

         return this;

       }

       public Builder MergeMessageExtension(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasMessageExtension &&

             result.messageExtension_ != global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance) {

             result.messageExtension_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.CreateBuilder(result.messageExtension_).MergeFrom(value).BuildPartial();

@@ -18197,6 +19760,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearMessageExtension() {

+        PrepareBuilder();

         result.hasMessageExtension = false;

         result.messageExtension_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance;

         return this;

@@ -18211,18 +19775,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetDynamicMessageExtension(global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDynamicMessageExtension = true;

         result.dynamicMessageExtension_ = value;

         return this;

       }

       public Builder SetDynamicMessageExtension(global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasDynamicMessageExtension = true;

         result.dynamicMessageExtension_ = builderForValue.Build();

         return this;

       }

       public Builder MergeDynamicMessageExtension(global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasDynamicMessageExtension &&

             result.dynamicMessageExtension_ != global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType.DefaultInstance) {

             result.dynamicMessageExtension_ = global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType.CreateBuilder(result.dynamicMessageExtension_).MergeFrom(value).BuildPartial();

@@ -18233,13 +19800,14 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearDynamicMessageExtension() {

+        PrepareBuilder();

         result.hasDynamicMessageExtension = false;

         result.dynamicMessageExtension_ = global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType.DefaultInstance;

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedExtensionList {

-        get { return result.repeatedExtension_; }

+        get { return PrepareBuilder().repeatedExtension_; }

       }

       public int RepeatedExtensionCount {

         get { return result.RepeatedExtensionCount; }

@@ -18249,25 +19817,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedExtension(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedExtension_[index] = value;

         return this;

       }

       public Builder AddRepeatedExtension(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedExtension_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedExtension(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedExtension_.Add(values);

         return this;

       }

       public Builder ClearRepeatedExtension() {

+        PrepareBuilder();

         result.repeatedExtension_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> PackedExtensionList {

-        get { return result.packedExtension_; }

+        get { return PrepareBuilder().packedExtension_; }

       }

       public int PackedExtensionCount {

         get { return result.PackedExtensionCount; }

@@ -18276,18 +19848,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedExtension(index);

       }

       public Builder SetPackedExtension(int index, int value) {

+        PrepareBuilder();

         result.packedExtension_[index] = value;

         return this;

       }

       public Builder AddPackedExtension(int value) {

+        PrepareBuilder();

         result.packedExtension_.Add(value);

         return this;

       }

       public Builder AddRangePackedExtension(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.packedExtension_.Add(values);

         return this;

       }

       public Builder ClearPackedExtension() {

+        PrepareBuilder();

         result.packedExtension_.Clear();

         return this;

       }

@@ -18522,7 +20098,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestRepeatedScalarDifferentTagSizes prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -18532,21 +20108,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestRepeatedScalarDifferentTagSizes();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestRepeatedScalarDifferentTagSizes cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestRepeatedScalarDifferentTagSizes result;

+      

+      private TestRepeatedScalarDifferentTagSizes PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestRepeatedScalarDifferentTagSizes original = result;

+          result = new TestRepeatedScalarDifferentTagSizes();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestRepeatedScalarDifferentTagSizes result = new TestRepeatedScalarDifferentTagSizes();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestRepeatedScalarDifferentTagSizes MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestRepeatedScalarDifferentTagSizes();

+        result = DefaultInstance ?? new TestRepeatedScalarDifferentTagSizes();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -18558,8 +20161,8 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestRepeatedScalarDifferentTagSizes BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.repeatedFixed32_.MakeReadOnly();

         result.repeatedInt32_.MakeReadOnly();

@@ -18567,9 +20170,8 @@ namespace Google.ProtocolBuffers.TestProtos {
         result.repeatedInt64_.MakeReadOnly();

         result.repeatedFloat_.MakeReadOnly();

         result.repeatedUint64_.MakeReadOnly();

-        TestRepeatedScalarDifferentTagSizes returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -18583,6 +20185,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestRepeatedScalarDifferentTagSizes other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestRepeatedScalarDifferentTagSizes.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.repeatedFixed32_.Count != 0) {

           result.repeatedFixed32_.Add(other.repeatedFixed32_);

         }

@@ -18610,6 +20213,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -18685,7 +20289,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> RepeatedFixed32List {

-        get { return result.repeatedFixed32_; }

+        get { return PrepareBuilder().repeatedFixed32_; }

       }

       public int RepeatedFixed32Count {

         get { return result.RepeatedFixed32Count; }

@@ -18696,26 +20300,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedFixed32(int index, uint value) {

+        PrepareBuilder();

         result.repeatedFixed32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedFixed32(uint value) {

+        PrepareBuilder();

         result.repeatedFixed32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedFixed32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.repeatedFixed32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFixed32() {

+        PrepareBuilder();

         result.repeatedFixed32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> RepeatedInt32List {

-        get { return result.repeatedInt32_; }

+        get { return PrepareBuilder().repeatedInt32_; }

       }

       public int RepeatedInt32Count {

         get { return result.RepeatedInt32Count; }

@@ -18724,25 +20332,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedInt32(index);

       }

       public Builder SetRepeatedInt32(int index, int value) {

+        PrepareBuilder();

         result.repeatedInt32_[index] = value;

         return this;

       }

       public Builder AddRepeatedInt32(int value) {

+        PrepareBuilder();

         result.repeatedInt32_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedInt32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.repeatedInt32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedInt32() {

+        PrepareBuilder();

         result.repeatedInt32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> RepeatedFixed64List {

-        get { return result.repeatedFixed64_; }

+        get { return PrepareBuilder().repeatedFixed64_; }

       }

       public int RepeatedFixed64Count {

         get { return result.RepeatedFixed64Count; }

@@ -18753,26 +20365,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedFixed64(int index, ulong value) {

+        PrepareBuilder();

         result.repeatedFixed64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedFixed64(ulong value) {

+        PrepareBuilder();

         result.repeatedFixed64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedFixed64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.repeatedFixed64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFixed64() {

+        PrepareBuilder();

         result.repeatedFixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> RepeatedInt64List {

-        get { return result.repeatedInt64_; }

+        get { return PrepareBuilder().repeatedInt64_; }

       }

       public int RepeatedInt64Count {

         get { return result.RepeatedInt64Count; }

@@ -18781,24 +20397,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedInt64(index);

       }

       public Builder SetRepeatedInt64(int index, long value) {

+        PrepareBuilder();

         result.repeatedInt64_[index] = value;

         return this;

       }

       public Builder AddRepeatedInt64(long value) {

+        PrepareBuilder();

         result.repeatedInt64_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedInt64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.repeatedInt64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedInt64() {

+        PrepareBuilder();

         result.repeatedInt64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<float> RepeatedFloatList {

-        get { return result.repeatedFloat_; }

+        get { return PrepareBuilder().repeatedFloat_; }

       }

       public int RepeatedFloatCount {

         get { return result.RepeatedFloatCount; }

@@ -18807,25 +20427,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedFloat(index);

       }

       public Builder SetRepeatedFloat(int index, float value) {

+        PrepareBuilder();

         result.repeatedFloat_[index] = value;

         return this;

       }

       public Builder AddRepeatedFloat(float value) {

+        PrepareBuilder();

         result.repeatedFloat_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedFloat(scg::IEnumerable<float> values) {

+        PrepareBuilder();

         result.repeatedFloat_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFloat() {

+        PrepareBuilder();

         result.repeatedFloat_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> RepeatedUint64List {

-        get { return result.repeatedUint64_; }

+        get { return PrepareBuilder().repeatedUint64_; }

       }

       public int RepeatedUint64Count {

         get { return result.RepeatedUint64Count; }

@@ -18836,20 +20460,24 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedUint64(int index, ulong value) {

+        PrepareBuilder();

         result.repeatedUint64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedUint64(ulong value) {

+        PrepareBuilder();

         result.repeatedUint64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedUint64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.repeatedUint64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedUint64() {

+        PrepareBuilder();

         result.repeatedUint64_.Clear();

         return this;

       }

@@ -18946,7 +20574,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(FooRequest prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -18956,21 +20584,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new FooRequest();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(FooRequest cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      FooRequest result = new FooRequest();

+      bool builderIsReadOnly;

+      FooRequest result;

+      

+      private FooRequest PrepareBuilder() {

+        if (builderIsReadOnly) {

+          FooRequest original = result;

+          result = new FooRequest();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override FooRequest MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new FooRequest();

+        result = DefaultInstance ?? new FooRequest();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -18982,12 +20637,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override FooRequest BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        FooRequest returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -19001,6 +20655,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(FooRequest other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.FooRequest.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -19010,6 +20665,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -19145,7 +20801,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(FooResponse prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -19155,21 +20811,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new FooResponse();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(FooResponse cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      FooResponse result;

+      

+      private FooResponse PrepareBuilder() {

+        if (builderIsReadOnly) {

+          FooResponse original = result;

+          result = new FooResponse();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      FooResponse result = new FooResponse();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override FooResponse MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new FooResponse();

+        result = DefaultInstance ?? new FooResponse();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -19181,12 +20864,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override FooResponse BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        FooResponse returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -19200,6 +20882,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(FooResponse other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.FooResponse.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -19209,6 +20892,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -19344,7 +21028,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(BarRequest prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -19354,21 +21038,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new BarRequest();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(BarRequest cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      BarRequest result;

+      

+      private BarRequest PrepareBuilder() {

+        if (builderIsReadOnly) {

+          BarRequest original = result;

+          result = new BarRequest();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      BarRequest result = new BarRequest();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override BarRequest MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new BarRequest();

+        result = DefaultInstance ?? new BarRequest();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -19380,12 +21091,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override BarRequest BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        BarRequest returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -19399,6 +21109,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(BarRequest other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.BarRequest.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -19408,6 +21119,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -19543,7 +21255,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(BarResponse prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -19553,21 +21265,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new BarResponse();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(BarResponse cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      BarResponse result = new BarResponse();

+      bool builderIsReadOnly;

+      BarResponse result;

+      

+      private BarResponse PrepareBuilder() {

+        if (builderIsReadOnly) {

+          BarResponse original = result;

+          result = new BarResponse();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override BarResponse MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new BarResponse();

+        result = DefaultInstance ?? new BarResponse();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -19579,12 +21318,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override BarResponse BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        BarResponse returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -19598,6 +21336,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(BarResponse other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.BarResponse.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -19607,6 +21346,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestRpcInterop.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestRpcInterop.cs
index a2a965eb..cb805861 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestRpcInterop.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestRpcInterop.cs
@@ -189,7 +189,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(SearchRequest prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -199,21 +199,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new SearchRequest();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(SearchRequest cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      SearchRequest result;

       

-      SearchRequest result = new SearchRequest();

+      private SearchRequest PrepareBuilder() {

+        if (builderIsReadOnly) {

+          SearchRequest original = result;

+          result = new SearchRequest();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override SearchRequest MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new SearchRequest();

+        result = DefaultInstance ?? new SearchRequest();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -225,13 +252,12 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override SearchRequest BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.criteria_.MakeReadOnly();

-        SearchRequest returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -245,6 +271,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(SearchRequest other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.SearchRequest.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.criteria_.Count != 0) {

           result.criteria_.Add(other.criteria_);

         }

@@ -257,6 +284,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -305,7 +333,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       

       public pbc::IPopsicleList<string> CriteriaList {

-        get { return result.criteria_; }

+        get { return PrepareBuilder().criteria_; }

       }

       public int CriteriaCount {

         get { return result.CriteriaCount; }

@@ -315,19 +343,23 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetCriteria(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.criteria_[index] = value;

         return this;

       }

       public Builder AddCriteria(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.criteria_.Add(value);

         return this;

       }

       public Builder AddRangeCriteria(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.criteria_.Add(values);

         return this;

       }

       public Builder ClearCriteria() {

+        PrepareBuilder();

         result.criteria_.Clear();

         return this;

       }

@@ -490,7 +522,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(ResultItem prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -500,21 +532,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new ResultItem();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(ResultItem cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          ResultItem result;

           

-          ResultItem result = new ResultItem();

+          private ResultItem PrepareBuilder() {

+            if (builderIsReadOnly) {

+              ResultItem original = result;

+              result = new ResultItem();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override ResultItem MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new ResultItem();

+            result = DefaultInstance ?? new ResultItem();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -526,12 +585,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override ResultItem BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            ResultItem returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -545,6 +603,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(ResultItem other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.SearchResponse.Types.ResultItem.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasUrl) {

               Url = other.Url;

             }

@@ -560,6 +619,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -620,11 +680,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetUrl(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasUrl = true;

             result.url_ = value;

             return this;

           }

           public Builder ClearUrl() {

+            PrepareBuilder();

             result.hasUrl = false;

             result.url_ = "";

             return this;

@@ -639,11 +701,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetName(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasName = true;

             result.name_ = value;

             return this;

           }

           public Builder ClearName() {

+            PrepareBuilder();

             result.hasName = false;

             result.name_ = "";

             return this;

@@ -737,7 +801,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(SearchResponse prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -747,21 +811,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new SearchResponse();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(SearchResponse cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      SearchResponse result;

       

-      SearchResponse result = new SearchResponse();

+      private SearchResponse PrepareBuilder() {

+        if (builderIsReadOnly) {

+          SearchResponse original = result;

+          result = new SearchResponse();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override SearchResponse MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new SearchResponse();

+        result = DefaultInstance ?? new SearchResponse();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -773,13 +864,12 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override SearchResponse BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.results_.MakeReadOnly();

-        SearchResponse returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -793,6 +883,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(SearchResponse other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.SearchResponse.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.results_.Count != 0) {

           result.results_.Add(other.results_);

         }

@@ -805,6 +896,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -853,7 +945,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.SearchResponse.Types.ResultItem> ResultsList {

-        get { return result.results_; }

+        get { return PrepareBuilder().results_; }

       }

       public int ResultsCount {

         get { return result.ResultsCount; }

@@ -863,29 +955,35 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetResults(int index, global::Google.ProtocolBuffers.TestProtos.SearchResponse.Types.ResultItem value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.results_[index] = value;

         return this;

       }

       public Builder SetResults(int index, global::Google.ProtocolBuffers.TestProtos.SearchResponse.Types.ResultItem.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.results_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddResults(global::Google.ProtocolBuffers.TestProtos.SearchResponse.Types.ResultItem value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.results_.Add(value);

         return this;

       }

       public Builder AddResults(global::Google.ProtocolBuffers.TestProtos.SearchResponse.Types.ResultItem.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.results_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeResults(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.SearchResponse.Types.ResultItem> values) {

+        PrepareBuilder();

         result.results_.Add(values);

         return this;

       }

       public Builder ClearResults() {

+        PrepareBuilder();

         result.results_.Clear();

         return this;

       }

@@ -1023,7 +1121,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(RefineSearchRequest prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1033,21 +1131,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new RefineSearchRequest();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(RefineSearchRequest cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      RefineSearchRequest result;

       

-      RefineSearchRequest result = new RefineSearchRequest();

+      private RefineSearchRequest PrepareBuilder() {

+        if (builderIsReadOnly) {

+          RefineSearchRequest original = result;

+          result = new RefineSearchRequest();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override RefineSearchRequest MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new RefineSearchRequest();

+        result = DefaultInstance ?? new RefineSearchRequest();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1059,13 +1184,12 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override RefineSearchRequest BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.criteria_.MakeReadOnly();

-        RefineSearchRequest returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1079,6 +1203,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(RefineSearchRequest other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.RefineSearchRequest.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.criteria_.Count != 0) {

           result.criteria_.Add(other.criteria_);

         }

@@ -1094,6 +1219,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1151,7 +1277,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       

       public pbc::IPopsicleList<string> CriteriaList {

-        get { return result.criteria_; }

+        get { return PrepareBuilder().criteria_; }

       }

       public int CriteriaCount {

         get { return result.CriteriaCount; }

@@ -1161,19 +1287,23 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetCriteria(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.criteria_[index] = value;

         return this;

       }

       public Builder AddCriteria(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.criteria_.Add(value);

         return this;

       }

       public Builder AddRangeCriteria(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.criteria_.Add(values);

         return this;

       }

       public Builder ClearCriteria() {

+        PrepareBuilder();

         result.criteria_.Clear();

         return this;

       }

@@ -1187,18 +1317,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetPreviousResults(global::Google.ProtocolBuffers.TestProtos.SearchResponse value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasPreviousResults = true;

         result.previousResults_ = value;

         return this;

       }

       public Builder SetPreviousResults(global::Google.ProtocolBuffers.TestProtos.SearchResponse.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasPreviousResults = true;

         result.previousResults_ = builderForValue.Build();

         return this;

       }

       public Builder MergePreviousResults(global::Google.ProtocolBuffers.TestProtos.SearchResponse value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasPreviousResults &&

             result.previousResults_ != global::Google.ProtocolBuffers.TestProtos.SearchResponse.DefaultInstance) {

             result.previousResults_ = global::Google.ProtocolBuffers.TestProtos.SearchResponse.CreateBuilder(result.previousResults_).MergeFrom(value).BuildPartial();

@@ -1209,6 +1342,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearPreviousResults() {

+        PrepareBuilder();

         result.hasPreviousResults = false;

         result.previousResults_ = global::Google.ProtocolBuffers.TestProtos.SearchResponse.DefaultInstance;

         return this;

diff --git a/src/ProtocolBuffers.Test/TestProtos/UnitTestXmlSerializerTestProtoFile.cs b/src/ProtocolBuffers.Test/TestProtos/UnitTestXmlSerializerTestProtoFile.cs
index ca0be5ab..798f09ad 100644
--- a/src/ProtocolBuffers.Test/TestProtos/UnitTestXmlSerializerTestProtoFile.cs
+++ b/src/ProtocolBuffers.Test/TestProtos/UnitTestXmlSerializerTestProtoFile.cs
@@ -263,7 +263,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestXmlChild prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.SerializableAttribute()]

@@ -274,21 +274,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestXmlChild();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestXmlChild cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestXmlChild result = new TestXmlChild();

+      bool builderIsReadOnly;

+      TestXmlChild result;

+      

+      private TestXmlChild PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestXmlChild original = result;

+          result = new TestXmlChild();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestXmlChild MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestXmlChild();

+        result = DefaultInstance ?? new TestXmlChild();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -300,13 +327,12 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestXmlChild BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.options_.MakeReadOnly();

-        TestXmlChild returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -320,6 +346,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestXmlChild other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestXmlChild.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.options_.Count != 0) {

           result.options_.Add(other.options_);

         }

@@ -335,6 +362,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -397,7 +425,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.EnumOptions> OptionsList {

-        get { return result.options_; }

+        get { return PrepareBuilder().options_; }

       }

       public int OptionsCount {

         get { return result.OptionsCount; }

@@ -406,18 +434,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetOptions(index);

       }

       public Builder SetOptions(int index, global::Google.ProtocolBuffers.TestProtos.EnumOptions value) {

+        PrepareBuilder();

         result.options_[index] = value;

         return this;

       }

       public Builder AddOptions(global::Google.ProtocolBuffers.TestProtos.EnumOptions value) {

+        PrepareBuilder();

         result.options_.Add(value);

         return this;

       }

       public Builder AddRangeOptions(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.EnumOptions> values) {

+        PrepareBuilder();

         result.options_.Add(values);

         return this;

       }

       public Builder ClearOptions() {

+        PrepareBuilder();

         result.options_.Clear();

         return this;

       }

@@ -431,11 +463,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetBinary(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasBinary = true;

         result.binary_ = value;

         return this;

       }

       public Builder ClearBinary() {

+        PrepareBuilder();

         result.hasBinary = false;

         result.binary_ = pb::ByteString.Empty;

         return this;

@@ -534,7 +568,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestXmlNoFields prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.SerializableAttribute()]

@@ -545,21 +579,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestXmlNoFields();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestXmlNoFields cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestXmlNoFields result = new TestXmlNoFields();

+      bool builderIsReadOnly;

+      TestXmlNoFields result;

+      

+      private TestXmlNoFields PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestXmlNoFields original = result;

+          result = new TestXmlNoFields();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestXmlNoFields MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestXmlNoFields();

+        result = DefaultInstance ?? new TestXmlNoFields();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -571,12 +632,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestXmlNoFields BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestXmlNoFields returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -590,6 +650,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestXmlNoFields other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestXmlNoFields.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -599,6 +660,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -751,7 +813,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestXmlRescursive prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.SerializableAttribute()]

@@ -762,21 +824,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestXmlRescursive();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestXmlRescursive cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestXmlRescursive result = new TestXmlRescursive();

+      bool builderIsReadOnly;

+      TestXmlRescursive result;

+      

+      private TestXmlRescursive PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestXmlRescursive original = result;

+          result = new TestXmlRescursive();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestXmlRescursive MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestXmlRescursive();

+        result = DefaultInstance ?? new TestXmlRescursive();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -788,12 +877,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestXmlRescursive BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestXmlRescursive returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -807,6 +895,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestXmlRescursive other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestXmlRescursive.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasChild) {

           MergeChild(other.Child);

         }

@@ -819,6 +908,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -880,18 +970,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetChild(global::Google.ProtocolBuffers.TestProtos.TestXmlRescursive value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasChild = true;

         result.child_ = value;

         return this;

       }

       public Builder SetChild(global::Google.ProtocolBuffers.TestProtos.TestXmlRescursive.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasChild = true;

         result.child_ = builderForValue.Build();

         return this;

       }

       public Builder MergeChild(global::Google.ProtocolBuffers.TestProtos.TestXmlRescursive value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasChild &&

             result.child_ != global::Google.ProtocolBuffers.TestProtos.TestXmlRescursive.DefaultInstance) {

             result.child_ = global::Google.ProtocolBuffers.TestProtos.TestXmlRescursive.CreateBuilder(result.child_).MergeFrom(value).BuildPartial();

@@ -902,6 +995,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearChild() {

+        PrepareBuilder();

         result.hasChild = false;

         result.child_ = global::Google.ProtocolBuffers.TestProtos.TestXmlRescursive.DefaultInstance;

         return this;

@@ -1075,7 +1169,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(Children prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.SerializableAttribute()]

@@ -1086,21 +1180,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new Children();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(Children cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

           

-          Children result = new Children();

+          bool builderIsReadOnly;

+          Children result;

+          

+          private Children PrepareBuilder() {

+            if (builderIsReadOnly) {

+              Children original = result;

+              result = new Children();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override Children MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new Children();

+            result = DefaultInstance ?? new Children();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -1112,13 +1233,12 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Children BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

             result.options_.MakeReadOnly();

-            Children returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -1132,6 +1252,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(Children other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestXmlMessage.Types.Children.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.options_.Count != 0) {

               result.options_.Add(other.options_);

             }

@@ -1147,6 +1268,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -1209,7 +1331,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           

           public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.EnumOptions> OptionsList {

-            get { return result.options_; }

+            get { return PrepareBuilder().options_; }

           }

           public int OptionsCount {

             get { return result.OptionsCount; }

@@ -1218,18 +1340,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             return result.GetOptions(index);

           }

           public Builder SetOptions(int index, global::Google.ProtocolBuffers.TestProtos.EnumOptions value) {

+            PrepareBuilder();

             result.options_[index] = value;

             return this;

           }

           public Builder AddOptions(global::Google.ProtocolBuffers.TestProtos.EnumOptions value) {

+            PrepareBuilder();

             result.options_.Add(value);

             return this;

           }

           public Builder AddRangeOptions(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.EnumOptions> values) {

+            PrepareBuilder();

             result.options_.Add(values);

             return this;

           }

           public Builder ClearOptions() {

+            PrepareBuilder();

             result.options_.Clear();

             return this;

           }

@@ -1243,11 +1369,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetBinary(pb::ByteString value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasBinary = true;

             result.binary_ = value;

             return this;

           }

           public Builder ClearBinary() {

+            PrepareBuilder();

             result.hasBinary = false;

             result.binary_ = pb::ByteString.Empty;

             return this;

@@ -1452,7 +1580,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestXmlMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.SerializableAttribute()]

@@ -1463,21 +1591,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestXmlMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestXmlMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestXmlMessage result = new TestXmlMessage();

+      bool builderIsReadOnly;

+      TestXmlMessage result;

+      

+      private TestXmlMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestXmlMessage original = result;

+          result = new TestXmlMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestXmlMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestXmlMessage();

+        result = DefaultInstance ?? new TestXmlMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1489,15 +1644,14 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestXmlMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.numbers_.MakeReadOnly();

         result.textlines_.MakeReadOnly();

         result.children_.MakeReadOnly();

-        TestXmlMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1511,6 +1665,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestXmlMessage other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestXmlMessage.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasNumber) {

           Number = other.Number;

         }

@@ -1542,6 +1697,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1627,18 +1783,20 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetNumber(value); }

       }

       public Builder SetNumber(long value) {

+        PrepareBuilder();

         result.hasNumber = true;

         result.number_ = value;

         return this;

       }

       public Builder ClearNumber() {

+        PrepareBuilder();

         result.hasNumber = false;

         result.number_ = 0L;

         return this;

       }

       

       public pbc::IPopsicleList<int> NumbersList {

-        get { return result.numbers_; }

+        get { return PrepareBuilder().numbers_; }

       }

       public int NumbersCount {

         get { return result.NumbersCount; }

@@ -1647,18 +1805,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetNumbers(index);

       }

       public Builder SetNumbers(int index, int value) {

+        PrepareBuilder();

         result.numbers_[index] = value;

         return this;

       }

       public Builder AddNumbers(int value) {

+        PrepareBuilder();

         result.numbers_.Add(value);

         return this;

       }

       public Builder AddRangeNumbers(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.numbers_.Add(values);

         return this;

       }

       public Builder ClearNumbers() {

+        PrepareBuilder();

         result.numbers_.Clear();

         return this;

       }

@@ -1672,18 +1834,20 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetText(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasText = true;

         result.text_ = value;

         return this;

       }

       public Builder ClearText() {

+        PrepareBuilder();

         result.hasText = false;

         result.text_ = "";

         return this;

       }

       

       public pbc::IPopsicleList<string> TextlinesList {

-        get { return result.textlines_; }

+        get { return PrepareBuilder().textlines_; }

       }

       public int TextlinesCount {

         get { return result.TextlinesCount; }

@@ -1693,19 +1857,23 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetTextlines(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.textlines_[index] = value;

         return this;

       }

       public Builder AddTextlines(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.textlines_.Add(value);

         return this;

       }

       public Builder AddRangeTextlines(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.textlines_.Add(values);

         return this;

       }

       public Builder ClearTextlines() {

+        PrepareBuilder();

         result.textlines_.Clear();

         return this;

       }

@@ -1718,11 +1886,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetValid(value); }

       }

       public Builder SetValid(bool value) {

+        PrepareBuilder();

         result.hasValid = true;

         result.valid_ = value;

         return this;

       }

       public Builder ClearValid() {

+        PrepareBuilder();

         result.hasValid = false;

         result.valid_ = false;

         return this;

@@ -1737,18 +1907,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetChild(global::Google.ProtocolBuffers.TestProtos.TestXmlChild value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasChild = true;

         result.child_ = value;

         return this;

       }

       public Builder SetChild(global::Google.ProtocolBuffers.TestProtos.TestXmlChild.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasChild = true;

         result.child_ = builderForValue.Build();

         return this;

       }

       public Builder MergeChild(global::Google.ProtocolBuffers.TestProtos.TestXmlChild value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasChild &&

             result.child_ != global::Google.ProtocolBuffers.TestProtos.TestXmlChild.DefaultInstance) {

             result.child_ = global::Google.ProtocolBuffers.TestProtos.TestXmlChild.CreateBuilder(result.child_).MergeFrom(value).BuildPartial();

@@ -1759,13 +1932,14 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearChild() {

+        PrepareBuilder();

         result.hasChild = false;

         result.child_ = global::Google.ProtocolBuffers.TestProtos.TestXmlChild.DefaultInstance;

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestXmlMessage.Types.Children> ChildrenList {

-        get { return result.children_; }

+        get { return PrepareBuilder().children_; }

       }

       public int ChildrenCount {

         get { return result.ChildrenCount; }

@@ -1775,29 +1949,35 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetChildren(int index, global::Google.ProtocolBuffers.TestProtos.TestXmlMessage.Types.Children value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.children_[index] = value;

         return this;

       }

       public Builder SetChildren(int index, global::Google.ProtocolBuffers.TestProtos.TestXmlMessage.Types.Children.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.children_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddChildren(global::Google.ProtocolBuffers.TestProtos.TestXmlMessage.Types.Children value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.children_.Add(value);

         return this;

       }

       public Builder AddChildren(global::Google.ProtocolBuffers.TestProtos.TestXmlMessage.Types.Children.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.children_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeChildren(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestXmlMessage.Types.Children> values) {

+        PrepareBuilder();

         result.children_.Add(values);

         return this;

       }

       public Builder ClearChildren() {

+        PrepareBuilder();

         result.children_.Clear();

         return this;

       }

@@ -1912,7 +2092,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestXmlExtension prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.SerializableAttribute()]

@@ -1923,21 +2103,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestXmlExtension();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestXmlExtension cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestXmlExtension result = new TestXmlExtension();

+      bool builderIsReadOnly;

+      TestXmlExtension result;

+      

+      private TestXmlExtension PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestXmlExtension original = result;

+          result = new TestXmlExtension();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestXmlExtension MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestXmlExtension();

+        result = DefaultInstance ?? new TestXmlExtension();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1949,12 +2156,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestXmlExtension BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestXmlExtension returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1968,6 +2174,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestXmlExtension other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestXmlExtension.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasNumber) {

           Number = other.Number;

         }

@@ -1980,6 +2187,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -2035,11 +2243,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetNumber(value); }

       }

       public Builder SetNumber(int value) {

+        PrepareBuilder();

         result.hasNumber = true;

         result.number_ = value;

         return this;

       }

       public Builder ClearNumber() {

+        PrepareBuilder();

         result.hasNumber = false;

         result.number_ = 0;

         return this;

diff --git a/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs b/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs
index 76cb1fee..2bebb011 100644
--- a/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs
+++ b/src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs
@@ -433,7 +433,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(CSharpFileOptions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -443,21 +443,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new CSharpFileOptions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(CSharpFileOptions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      CSharpFileOptions result;

       

-      CSharpFileOptions result = new CSharpFileOptions();

+      private CSharpFileOptions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          CSharpFileOptions original = result;

+          result = new CSharpFileOptions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override CSharpFileOptions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new CSharpFileOptions();

+        result = DefaultInstance ?? new CSharpFileOptions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -469,12 +496,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override CSharpFileOptions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        CSharpFileOptions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -488,6 +514,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(CSharpFileOptions other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.CSharpFileOptions.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasNamespace) {

           Namespace = other.Namespace;

         }

@@ -539,6 +566,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -655,11 +683,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetNamespace(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasNamespace = true;

         result.namespace_ = value;

         return this;

       }

       public Builder ClearNamespace() {

+        PrepareBuilder();

         result.hasNamespace = false;

         result.namespace_ = "";

         return this;

@@ -674,11 +704,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetUmbrellaClassname(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasUmbrellaClassname = true;

         result.umbrellaClassname_ = value;

         return this;

       }

       public Builder ClearUmbrellaClassname() {

+        PrepareBuilder();

         result.hasUmbrellaClassname = false;

         result.umbrellaClassname_ = "";

         return this;

@@ -692,11 +724,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetPublicClasses(value); }

       }

       public Builder SetPublicClasses(bool value) {

+        PrepareBuilder();

         result.hasPublicClasses = true;

         result.publicClasses_ = value;

         return this;

       }

       public Builder ClearPublicClasses() {

+        PrepareBuilder();

         result.hasPublicClasses = false;

         result.publicClasses_ = true;

         return this;

@@ -710,11 +744,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetMultipleFiles(value); }

       }

       public Builder SetMultipleFiles(bool value) {

+        PrepareBuilder();

         result.hasMultipleFiles = true;

         result.multipleFiles_ = value;

         return this;

       }

       public Builder ClearMultipleFiles() {

+        PrepareBuilder();

         result.hasMultipleFiles = false;

         result.multipleFiles_ = false;

         return this;

@@ -728,11 +764,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetNestClasses(value); }

       }

       public Builder SetNestClasses(bool value) {

+        PrepareBuilder();

         result.hasNestClasses = true;

         result.nestClasses_ = value;

         return this;

       }

       public Builder ClearNestClasses() {

+        PrepareBuilder();

         result.hasNestClasses = false;

         result.nestClasses_ = false;

         return this;

@@ -746,11 +784,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetCodeContracts(value); }

       }

       public Builder SetCodeContracts(bool value) {

+        PrepareBuilder();

         result.hasCodeContracts = true;

         result.codeContracts_ = value;

         return this;

       }

       public Builder ClearCodeContracts() {

+        PrepareBuilder();

         result.hasCodeContracts = false;

         result.codeContracts_ = false;

         return this;

@@ -764,11 +804,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetExpandNamespaceDirectories(value); }

       }

       public Builder SetExpandNamespaceDirectories(bool value) {

+        PrepareBuilder();

         result.hasExpandNamespaceDirectories = true;

         result.expandNamespaceDirectories_ = value;

         return this;

       }

       public Builder ClearExpandNamespaceDirectories() {

+        PrepareBuilder();

         result.hasExpandNamespaceDirectories = false;

         result.expandNamespaceDirectories_ = false;

         return this;

@@ -782,11 +824,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetClsCompliance(value); }

       }

       public Builder SetClsCompliance(bool value) {

+        PrepareBuilder();

         result.hasClsCompliance = true;

         result.clsCompliance_ = value;

         return this;

       }

       public Builder ClearClsCompliance() {

+        PrepareBuilder();

         result.hasClsCompliance = false;

         result.clsCompliance_ = true;

         return this;

@@ -800,11 +844,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetAddSerializable(value); }

       }

       public Builder SetAddSerializable(bool value) {

+        PrepareBuilder();

         result.hasAddSerializable = true;

         result.addSerializable_ = value;

         return this;

       }

       public Builder ClearAddSerializable() {

+        PrepareBuilder();

         result.hasAddSerializable = false;

         result.addSerializable_ = false;

         return this;

@@ -819,11 +865,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetFileExtension(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasFileExtension = true;

         result.fileExtension_ = value;

         return this;

       }

       public Builder ClearFileExtension() {

+        PrepareBuilder();

         result.hasFileExtension = false;

         result.fileExtension_ = ".cs";

         return this;

@@ -838,11 +886,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetUmbrellaNamespace(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasUmbrellaNamespace = true;

         result.umbrellaNamespace_ = value;

         return this;

       }

       public Builder ClearUmbrellaNamespace() {

+        PrepareBuilder();

         result.hasUmbrellaNamespace = false;

         result.umbrellaNamespace_ = "";

         return this;

@@ -857,11 +907,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetOutputDirectory(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOutputDirectory = true;

         result.outputDirectory_ = value;

         return this;

       }

       public Builder ClearOutputDirectory() {

+        PrepareBuilder();

         result.hasOutputDirectory = false;

         result.outputDirectory_ = ".";

         return this;

@@ -875,11 +927,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetIgnoreGoogleProtobuf(value); }

       }

       public Builder SetIgnoreGoogleProtobuf(bool value) {

+        PrepareBuilder();

         result.hasIgnoreGoogleProtobuf = true;

         result.ignoreGoogleProtobuf_ = value;

         return this;

       }

       public Builder ClearIgnoreGoogleProtobuf() {

+        PrepareBuilder();

         result.hasIgnoreGoogleProtobuf = false;

         result.ignoreGoogleProtobuf_ = false;

         return this;

@@ -893,11 +947,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetServiceGeneratorType(value); }

       }

       public Builder SetServiceGeneratorType(global::Google.ProtocolBuffers.DescriptorProtos.CSharpServiceType value) {

+        PrepareBuilder();

         result.hasServiceGeneratorType = true;

         result.serviceGeneratorType_ = value;

         return this;

       }

       public Builder ClearServiceGeneratorType() {

+        PrepareBuilder();

         result.hasServiceGeneratorType = false;

         result.serviceGeneratorType_ = global::Google.ProtocolBuffers.DescriptorProtos.CSharpServiceType.NONE;

         return this;

@@ -1011,7 +1067,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(CSharpFieldOptions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1021,21 +1077,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new CSharpFieldOptions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(CSharpFieldOptions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      CSharpFieldOptions result;

       

-      CSharpFieldOptions result = new CSharpFieldOptions();

+      private CSharpFieldOptions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          CSharpFieldOptions original = result;

+          result = new CSharpFieldOptions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override CSharpFieldOptions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new CSharpFieldOptions();

+        result = DefaultInstance ?? new CSharpFieldOptions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1047,12 +1130,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override CSharpFieldOptions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        CSharpFieldOptions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1066,6 +1148,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(CSharpFieldOptions other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.CSharpFieldOptions.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasPropertyName) {

           PropertyName = other.PropertyName;

         }

@@ -1078,6 +1161,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1134,11 +1218,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetPropertyName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasPropertyName = true;

         result.propertyName_ = value;

         return this;

       }

       public Builder ClearPropertyName() {

+        PrepareBuilder();

         result.hasPropertyName = false;

         result.propertyName_ = "";

         return this;

@@ -1252,7 +1338,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(CSharpServiceOptions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1262,21 +1348,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new CSharpServiceOptions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(CSharpServiceOptions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      CSharpServiceOptions result;

       

-      CSharpServiceOptions result = new CSharpServiceOptions();

+      private CSharpServiceOptions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          CSharpServiceOptions original = result;

+          result = new CSharpServiceOptions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override CSharpServiceOptions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new CSharpServiceOptions();

+        result = DefaultInstance ?? new CSharpServiceOptions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1288,12 +1401,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override CSharpServiceOptions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        CSharpServiceOptions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1307,6 +1419,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(CSharpServiceOptions other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.CSharpServiceOptions.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasInterfaceId) {

           InterfaceId = other.InterfaceId;

         }

@@ -1319,6 +1432,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1375,11 +1489,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetInterfaceId(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasInterfaceId = true;

         result.interfaceId_ = value;

         return this;

       }

       public Builder ClearInterfaceId() {

+        PrepareBuilder();

         result.hasInterfaceId = false;

         result.interfaceId_ = "";

         return this;

@@ -1493,7 +1609,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(CSharpMethodOptions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1503,21 +1619,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new CSharpMethodOptions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(CSharpMethodOptions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      CSharpMethodOptions result;

       

-      CSharpMethodOptions result = new CSharpMethodOptions();

+      private CSharpMethodOptions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          CSharpMethodOptions original = result;

+          result = new CSharpMethodOptions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override CSharpMethodOptions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new CSharpMethodOptions();

+        result = DefaultInstance ?? new CSharpMethodOptions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1529,12 +1672,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override CSharpMethodOptions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        CSharpMethodOptions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1548,6 +1690,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(CSharpMethodOptions other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.CSharpMethodOptions.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasDispatchId) {

           DispatchId = other.DispatchId;

         }

@@ -1560,6 +1703,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1615,11 +1759,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetDispatchId(value); }

       }

       public Builder SetDispatchId(int value) {

+        PrepareBuilder();

         result.hasDispatchId = true;

         result.dispatchId_ = value;

         return this;

       }

       public Builder ClearDispatchId() {

+        PrepareBuilder();

         result.hasDispatchId = false;

         result.dispatchId_ = 0;

         return this;

diff --git a/src/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs b/src/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
index ff5429d8..de6e2ed8 100644
--- a/src/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
+++ b/src/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
@@ -337,7 +337,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(FileDescriptorSet prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -347,21 +347,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new FileDescriptorSet();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(FileDescriptorSet cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      FileDescriptorSet result;

       

-      FileDescriptorSet result = new FileDescriptorSet();

+      private FileDescriptorSet PrepareBuilder() {

+        if (builderIsReadOnly) {

+          FileDescriptorSet original = result;

+          result = new FileDescriptorSet();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override FileDescriptorSet MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new FileDescriptorSet();

+        result = DefaultInstance ?? new FileDescriptorSet();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -373,13 +400,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override FileDescriptorSet BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.file_.MakeReadOnly();

-        FileDescriptorSet returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -393,6 +419,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(FileDescriptorSet other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorSet.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.file_.Count != 0) {

           result.file_.Add(other.file_);

         }

@@ -405,6 +432,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -453,7 +481,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto> FileList {

-        get { return result.file_; }

+        get { return PrepareBuilder().file_; }

       }

       public int FileCount {

         get { return result.FileCount; }

@@ -463,29 +491,35 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetFile(int index, global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.file_[index] = value;

         return this;

       }

       public Builder SetFile(int index, global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.file_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddFile(global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.file_.Add(value);

         return this;

       }

       public Builder AddFile(global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.file_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeFile(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto> values) {

+        PrepareBuilder();

         result.file_.Add(values);

         return this;

       }

       public Builder ClearFile() {

+        PrepareBuilder();

         result.file_.Clear();

         return this;

       }

@@ -740,7 +774,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(FileDescriptorProto prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -750,21 +784,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new FileDescriptorProto();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(FileDescriptorProto cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      FileDescriptorProto result = new FileDescriptorProto();

+      bool builderIsReadOnly;

+      FileDescriptorProto result;

+      

+      private FileDescriptorProto PrepareBuilder() {

+        if (builderIsReadOnly) {

+          FileDescriptorProto original = result;

+          result = new FileDescriptorProto();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override FileDescriptorProto MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new FileDescriptorProto();

+        result = DefaultInstance ?? new FileDescriptorProto();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -776,17 +837,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override FileDescriptorProto BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.dependency_.MakeReadOnly();

         result.messageType_.MakeReadOnly();

         result.enumType_.MakeReadOnly();

         result.service_.MakeReadOnly();

         result.extension_.MakeReadOnly();

-        FileDescriptorProto returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -800,6 +860,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(FileDescriptorProto other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasName) {

           Name = other.Name;

         }

@@ -833,6 +894,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -922,11 +984,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasName = true;

         result.name_ = value;

         return this;

       }

       public Builder ClearName() {

+        PrepareBuilder();

         result.hasName = false;

         result.name_ = "";

         return this;

@@ -941,18 +1005,20 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetPackage(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasPackage = true;

         result.package_ = value;

         return this;

       }

       public Builder ClearPackage() {

+        PrepareBuilder();

         result.hasPackage = false;

         result.package_ = "";

         return this;

       }

       

       public pbc::IPopsicleList<string> DependencyList {

-        get { return result.dependency_; }

+        get { return PrepareBuilder().dependency_; }

       }

       public int DependencyCount {

         get { return result.DependencyCount; }

@@ -962,25 +1028,29 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetDependency(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.dependency_[index] = value;

         return this;

       }

       public Builder AddDependency(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.dependency_.Add(value);

         return this;

       }

       public Builder AddRangeDependency(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.dependency_.Add(values);

         return this;

       }

       public Builder ClearDependency() {

+        PrepareBuilder();

         result.dependency_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto> MessageTypeList {

-        get { return result.messageType_; }

+        get { return PrepareBuilder().messageType_; }

       }

       public int MessageTypeCount {

         get { return result.MessageTypeCount; }

@@ -990,35 +1060,41 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetMessageType(int index, global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.messageType_[index] = value;

         return this;

       }

       public Builder SetMessageType(int index, global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.messageType_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddMessageType(global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.messageType_.Add(value);

         return this;

       }

       public Builder AddMessageType(global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.messageType_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeMessageType(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto> values) {

+        PrepareBuilder();

         result.messageType_.Add(values);

         return this;

       }

       public Builder ClearMessageType() {

+        PrepareBuilder();

         result.messageType_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto> EnumTypeList {

-        get { return result.enumType_; }

+        get { return PrepareBuilder().enumType_; }

       }

       public int EnumTypeCount {

         get { return result.EnumTypeCount; }

@@ -1028,35 +1104,41 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetEnumType(int index, global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.enumType_[index] = value;

         return this;

       }

       public Builder SetEnumType(int index, global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.enumType_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddEnumType(global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.enumType_.Add(value);

         return this;

       }

       public Builder AddEnumType(global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.enumType_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeEnumType(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto> values) {

+        PrepareBuilder();

         result.enumType_.Add(values);

         return this;

       }

       public Builder ClearEnumType() {

+        PrepareBuilder();

         result.enumType_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto> ServiceList {

-        get { return result.service_; }

+        get { return PrepareBuilder().service_; }

       }

       public int ServiceCount {

         get { return result.ServiceCount; }

@@ -1066,35 +1148,41 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetService(int index, global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.service_[index] = value;

         return this;

       }

       public Builder SetService(int index, global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.service_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddService(global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.service_.Add(value);

         return this;

       }

       public Builder AddService(global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.service_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeService(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto> values) {

+        PrepareBuilder();

         result.service_.Add(values);

         return this;

       }

       public Builder ClearService() {

+        PrepareBuilder();

         result.service_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> ExtensionList {

-        get { return result.extension_; }

+        get { return PrepareBuilder().extension_; }

       }

       public int ExtensionCount {

         get { return result.ExtensionCount; }

@@ -1104,29 +1192,35 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetExtension(int index, global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.extension_[index] = value;

         return this;

       }

       public Builder SetExtension(int index, global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.extension_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddExtension(global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.extension_.Add(value);

         return this;

       }

       public Builder AddExtension(global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.extension_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeExtension(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> values) {

+        PrepareBuilder();

         result.extension_.Add(values);

         return this;

       }

       public Builder ClearExtension() {

+        PrepareBuilder();

         result.extension_.Clear();

         return this;

       }

@@ -1140,18 +1234,21 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetOptions(global::Google.ProtocolBuffers.DescriptorProtos.FileOptions value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptions = true;

         result.options_ = value;

         return this;

       }

       public Builder SetOptions(global::Google.ProtocolBuffers.DescriptorProtos.FileOptions.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptions = true;

         result.options_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptions(global::Google.ProtocolBuffers.DescriptorProtos.FileOptions value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptions &&

             result.options_ != global::Google.ProtocolBuffers.DescriptorProtos.FileOptions.DefaultInstance) {

             result.options_ = global::Google.ProtocolBuffers.DescriptorProtos.FileOptions.CreateBuilder(result.options_).MergeFrom(value).BuildPartial();

@@ -1162,6 +1259,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;

       }

       public Builder ClearOptions() {

+        PrepareBuilder();

         result.hasOptions = false;

         result.options_ = global::Google.ProtocolBuffers.DescriptorProtos.FileOptions.DefaultInstance;

         return this;

@@ -1324,7 +1422,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(ExtensionRange prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1334,21 +1432,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new ExtensionRange();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(ExtensionRange cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

           

-          ExtensionRange result = new ExtensionRange();

+          bool builderIsReadOnly;

+          ExtensionRange result;

+          

+          private ExtensionRange PrepareBuilder() {

+            if (builderIsReadOnly) {

+              ExtensionRange original = result;

+              result = new ExtensionRange();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override ExtensionRange MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new ExtensionRange();

+            result = DefaultInstance ?? new ExtensionRange();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -1360,12 +1485,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           }

           

           public override ExtensionRange BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            ExtensionRange returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -1379,6 +1503,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           

           public override Builder MergeFrom(ExtensionRange other) {

             if (other == global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasStart) {

               Start = other.Start;

             }

@@ -1394,6 +1519,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -1453,11 +1579,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
             set { SetStart(value); }

           }

           public Builder SetStart(int value) {

+            PrepareBuilder();

             result.hasStart = true;

             result.start_ = value;

             return this;

           }

           public Builder ClearStart() {

+            PrepareBuilder();

             result.hasStart = false;

             result.start_ = 0;

             return this;

@@ -1471,11 +1599,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
             set { SetEnd(value); }

           }

           public Builder SetEnd(int value) {

+            PrepareBuilder();

             result.hasEnd = true;

             result.end_ = value;

             return this;

           }

           public Builder ClearEnd() {

+            PrepareBuilder();

             result.hasEnd = false;

             result.end_ = 0;

             return this;

@@ -1685,7 +1815,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(DescriptorProto prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1695,21 +1825,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new DescriptorProto();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(DescriptorProto cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      DescriptorProto result;

+      

+      private DescriptorProto PrepareBuilder() {

+        if (builderIsReadOnly) {

+          DescriptorProto original = result;

+          result = new DescriptorProto();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      DescriptorProto result = new DescriptorProto();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override DescriptorProto MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new DescriptorProto();

+        result = DefaultInstance ?? new DescriptorProto();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1721,17 +1878,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override DescriptorProto BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.field_.MakeReadOnly();

         result.extension_.MakeReadOnly();

         result.nestedType_.MakeReadOnly();

         result.enumType_.MakeReadOnly();

         result.extensionRange_.MakeReadOnly();

-        DescriptorProto returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -1745,6 +1901,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(DescriptorProto other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasName) {

           Name = other.Name;

         }

@@ -1775,6 +1932,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -1860,18 +2018,20 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasName = true;

         result.name_ = value;

         return this;

       }

       public Builder ClearName() {

+        PrepareBuilder();

         result.hasName = false;

         result.name_ = "";

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> FieldList {

-        get { return result.field_; }

+        get { return PrepareBuilder().field_; }

       }

       public int FieldCount {

         get { return result.FieldCount; }

@@ -1881,35 +2041,41 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetField(int index, global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.field_[index] = value;

         return this;

       }

       public Builder SetField(int index, global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.field_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddField(global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.field_.Add(value);

         return this;

       }

       public Builder AddField(global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.field_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeField(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> values) {

+        PrepareBuilder();

         result.field_.Add(values);

         return this;

       }

       public Builder ClearField() {

+        PrepareBuilder();

         result.field_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> ExtensionList {

-        get { return result.extension_; }

+        get { return PrepareBuilder().extension_; }

       }

       public int ExtensionCount {

         get { return result.ExtensionCount; }

@@ -1919,35 +2085,41 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetExtension(int index, global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.extension_[index] = value;

         return this;

       }

       public Builder SetExtension(int index, global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.extension_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddExtension(global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.extension_.Add(value);

         return this;

       }

       public Builder AddExtension(global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.extension_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeExtension(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> values) {

+        PrepareBuilder();

         result.extension_.Add(values);

         return this;

       }

       public Builder ClearExtension() {

+        PrepareBuilder();

         result.extension_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto> NestedTypeList {

-        get { return result.nestedType_; }

+        get { return PrepareBuilder().nestedType_; }

       }

       public int NestedTypeCount {

         get { return result.NestedTypeCount; }

@@ -1957,35 +2129,41 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetNestedType(int index, global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.nestedType_[index] = value;

         return this;

       }

       public Builder SetNestedType(int index, global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.nestedType_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddNestedType(global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.nestedType_.Add(value);

         return this;

       }

       public Builder AddNestedType(global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.nestedType_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeNestedType(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto> values) {

+        PrepareBuilder();

         result.nestedType_.Add(values);

         return this;

       }

       public Builder ClearNestedType() {

+        PrepareBuilder();

         result.nestedType_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto> EnumTypeList {

-        get { return result.enumType_; }

+        get { return PrepareBuilder().enumType_; }

       }

       public int EnumTypeCount {

         get { return result.EnumTypeCount; }

@@ -1995,35 +2173,41 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetEnumType(int index, global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.enumType_[index] = value;

         return this;

       }

       public Builder SetEnumType(int index, global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.enumType_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddEnumType(global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.enumType_.Add(value);

         return this;

       }

       public Builder AddEnumType(global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.enumType_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeEnumType(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto> values) {

+        PrepareBuilder();

         result.enumType_.Add(values);

         return this;

       }

       public Builder ClearEnumType() {

+        PrepareBuilder();

         result.enumType_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange> ExtensionRangeList {

-        get { return result.extensionRange_; }

+        get { return PrepareBuilder().extensionRange_; }

       }

       public int ExtensionRangeCount {

         get { return result.ExtensionRangeCount; }

@@ -2033,29 +2217,35 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetExtensionRange(int index, global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.extensionRange_[index] = value;

         return this;

       }

       public Builder SetExtensionRange(int index, global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.extensionRange_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddExtensionRange(global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.extensionRange_.Add(value);

         return this;

       }

       public Builder AddExtensionRange(global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.extensionRange_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeExtensionRange(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange> values) {

+        PrepareBuilder();

         result.extensionRange_.Add(values);

         return this;

       }

       public Builder ClearExtensionRange() {

+        PrepareBuilder();

         result.extensionRange_.Clear();

         return this;

       }

@@ -2069,18 +2259,21 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetOptions(global::Google.ProtocolBuffers.DescriptorProtos.MessageOptions value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptions = true;

         result.options_ = value;

         return this;

       }

       public Builder SetOptions(global::Google.ProtocolBuffers.DescriptorProtos.MessageOptions.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptions = true;

         result.options_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptions(global::Google.ProtocolBuffers.DescriptorProtos.MessageOptions value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptions &&

             result.options_ != global::Google.ProtocolBuffers.DescriptorProtos.MessageOptions.DefaultInstance) {

             result.options_ = global::Google.ProtocolBuffers.DescriptorProtos.MessageOptions.CreateBuilder(result.options_).MergeFrom(value).BuildPartial();

@@ -2091,6 +2284,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;

       }

       public Builder ClearOptions() {

+        PrepareBuilder();

         result.hasOptions = false;

         result.options_ = global::Google.ProtocolBuffers.DescriptorProtos.MessageOptions.DefaultInstance;

         return this;

@@ -2358,7 +2552,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(FieldDescriptorProto prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -2368,21 +2562,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new FieldDescriptorProto();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(FieldDescriptorProto cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      FieldDescriptorProto result;

       

-      FieldDescriptorProto result = new FieldDescriptorProto();

+      private FieldDescriptorProto PrepareBuilder() {

+        if (builderIsReadOnly) {

+          FieldDescriptorProto original = result;

+          result = new FieldDescriptorProto();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override FieldDescriptorProto MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new FieldDescriptorProto();

+        result = DefaultInstance ?? new FieldDescriptorProto();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -2394,12 +2615,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override FieldDescriptorProto BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        FieldDescriptorProto returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -2413,6 +2633,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(FieldDescriptorProto other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasName) {

           Name = other.Name;

         }

@@ -2446,6 +2667,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -2551,11 +2773,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasName = true;

         result.name_ = value;

         return this;

       }

       public Builder ClearName() {

+        PrepareBuilder();

         result.hasName = false;

         result.name_ = "";

         return this;

@@ -2569,11 +2793,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetNumber(value); }

       }

       public Builder SetNumber(int value) {

+        PrepareBuilder();

         result.hasNumber = true;

         result.number_ = value;

         return this;

       }

       public Builder ClearNumber() {

+        PrepareBuilder();

         result.hasNumber = false;

         result.number_ = 0;

         return this;

@@ -2587,11 +2813,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetLabel(value); }

       }

       public Builder SetLabel(global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto.Types.Label value) {

+        PrepareBuilder();

         result.hasLabel = true;

         result.label_ = value;

         return this;

       }

       public Builder ClearLabel() {

+        PrepareBuilder();

         result.hasLabel = false;

         result.label_ = global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto.Types.Label.LABEL_OPTIONAL;

         return this;

@@ -2605,11 +2833,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetType(value); }

       }

       public Builder SetType(global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto.Types.Type value) {

+        PrepareBuilder();

         result.hasType = true;

         result.type_ = value;

         return this;

       }

       public Builder ClearType() {

+        PrepareBuilder();

         result.hasType = false;

         result.type_ = global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto.Types.Type.TYPE_DOUBLE;

         return this;

@@ -2624,11 +2854,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetTypeName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasTypeName = true;

         result.typeName_ = value;

         return this;

       }

       public Builder ClearTypeName() {

+        PrepareBuilder();

         result.hasTypeName = false;

         result.typeName_ = "";

         return this;

@@ -2643,11 +2875,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetExtendee(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasExtendee = true;

         result.extendee_ = value;

         return this;

       }

       public Builder ClearExtendee() {

+        PrepareBuilder();

         result.hasExtendee = false;

         result.extendee_ = "";

         return this;

@@ -2662,11 +2896,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetDefaultValue(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDefaultValue = true;

         result.defaultValue_ = value;

         return this;

       }

       public Builder ClearDefaultValue() {

+        PrepareBuilder();

         result.hasDefaultValue = false;

         result.defaultValue_ = "";

         return this;

@@ -2681,18 +2917,21 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetOptions(global::Google.ProtocolBuffers.DescriptorProtos.FieldOptions value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptions = true;

         result.options_ = value;

         return this;

       }

       public Builder SetOptions(global::Google.ProtocolBuffers.DescriptorProtos.FieldOptions.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptions = true;

         result.options_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptions(global::Google.ProtocolBuffers.DescriptorProtos.FieldOptions value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptions &&

             result.options_ != global::Google.ProtocolBuffers.DescriptorProtos.FieldOptions.DefaultInstance) {

             result.options_ = global::Google.ProtocolBuffers.DescriptorProtos.FieldOptions.CreateBuilder(result.options_).MergeFrom(value).BuildPartial();

@@ -2703,6 +2942,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;

       }

       public Builder ClearOptions() {

+        PrepareBuilder();

         result.hasOptions = false;

         result.options_ = global::Google.ProtocolBuffers.DescriptorProtos.FieldOptions.DefaultInstance;

         return this;

@@ -2856,7 +3096,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(EnumDescriptorProto prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -2866,21 +3106,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new EnumDescriptorProto();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(EnumDescriptorProto cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      EnumDescriptorProto result;

+      

+      private EnumDescriptorProto PrepareBuilder() {

+        if (builderIsReadOnly) {

+          EnumDescriptorProto original = result;

+          result = new EnumDescriptorProto();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      EnumDescriptorProto result = new EnumDescriptorProto();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override EnumDescriptorProto MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new EnumDescriptorProto();

+        result = DefaultInstance ?? new EnumDescriptorProto();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -2892,13 +3159,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override EnumDescriptorProto BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.value_.MakeReadOnly();

-        EnumDescriptorProto returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -2912,6 +3178,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(EnumDescriptorProto other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasName) {

           Name = other.Name;

         }

@@ -2930,6 +3197,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -2999,18 +3267,20 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasName = true;

         result.name_ = value;

         return this;

       }

       public Builder ClearName() {

+        PrepareBuilder();

         result.hasName = false;

         result.name_ = "";

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto> ValueList {

-        get { return result.value_; }

+        get { return PrepareBuilder().value_; }

       }

       public int ValueCount {

         get { return result.ValueCount; }

@@ -3020,29 +3290,35 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetValue(int index, global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.value_[index] = value;

         return this;

       }

       public Builder SetValue(int index, global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.value_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddValue(global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.value_.Add(value);

         return this;

       }

       public Builder AddValue(global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.value_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeValue(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto> values) {

+        PrepareBuilder();

         result.value_.Add(values);

         return this;

       }

       public Builder ClearValue() {

+        PrepareBuilder();

         result.value_.Clear();

         return this;

       }

@@ -3056,18 +3332,21 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetOptions(global::Google.ProtocolBuffers.DescriptorProtos.EnumOptions value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptions = true;

         result.options_ = value;

         return this;

       }

       public Builder SetOptions(global::Google.ProtocolBuffers.DescriptorProtos.EnumOptions.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptions = true;

         result.options_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptions(global::Google.ProtocolBuffers.DescriptorProtos.EnumOptions value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptions &&

             result.options_ != global::Google.ProtocolBuffers.DescriptorProtos.EnumOptions.DefaultInstance) {

             result.options_ = global::Google.ProtocolBuffers.DescriptorProtos.EnumOptions.CreateBuilder(result.options_).MergeFrom(value).BuildPartial();

@@ -3078,6 +3357,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;

       }

       public Builder ClearOptions() {

+        PrepareBuilder();

         result.hasOptions = false;

         result.options_ = global::Google.ProtocolBuffers.DescriptorProtos.EnumOptions.DefaultInstance;

         return this;

@@ -3226,7 +3506,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(EnumValueDescriptorProto prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -3236,21 +3516,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new EnumValueDescriptorProto();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(EnumValueDescriptorProto cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      EnumValueDescriptorProto result = new EnumValueDescriptorProto();

+      bool builderIsReadOnly;

+      EnumValueDescriptorProto result;

+      

+      private EnumValueDescriptorProto PrepareBuilder() {

+        if (builderIsReadOnly) {

+          EnumValueDescriptorProto original = result;

+          result = new EnumValueDescriptorProto();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override EnumValueDescriptorProto MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new EnumValueDescriptorProto();

+        result = DefaultInstance ?? new EnumValueDescriptorProto();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -3262,12 +3569,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override EnumValueDescriptorProto BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        EnumValueDescriptorProto returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -3281,6 +3587,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(EnumValueDescriptorProto other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasName) {

           Name = other.Name;

         }

@@ -3299,6 +3606,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -3368,11 +3676,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasName = true;

         result.name_ = value;

         return this;

       }

       public Builder ClearName() {

+        PrepareBuilder();

         result.hasName = false;

         result.name_ = "";

         return this;

@@ -3386,11 +3696,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetNumber(value); }

       }

       public Builder SetNumber(int value) {

+        PrepareBuilder();

         result.hasNumber = true;

         result.number_ = value;

         return this;

       }

       public Builder ClearNumber() {

+        PrepareBuilder();

         result.hasNumber = false;

         result.number_ = 0;

         return this;

@@ -3405,18 +3717,21 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetOptions(global::Google.ProtocolBuffers.DescriptorProtos.EnumValueOptions value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptions = true;

         result.options_ = value;

         return this;

       }

       public Builder SetOptions(global::Google.ProtocolBuffers.DescriptorProtos.EnumValueOptions.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptions = true;

         result.options_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptions(global::Google.ProtocolBuffers.DescriptorProtos.EnumValueOptions value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptions &&

             result.options_ != global::Google.ProtocolBuffers.DescriptorProtos.EnumValueOptions.DefaultInstance) {

             result.options_ = global::Google.ProtocolBuffers.DescriptorProtos.EnumValueOptions.CreateBuilder(result.options_).MergeFrom(value).BuildPartial();

@@ -3427,6 +3742,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;

       }

       public Builder ClearOptions() {

+        PrepareBuilder();

         result.hasOptions = false;

         result.options_ = global::Google.ProtocolBuffers.DescriptorProtos.EnumValueOptions.DefaultInstance;

         return this;

@@ -3580,7 +3896,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(ServiceDescriptorProto prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -3590,21 +3906,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new ServiceDescriptorProto();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(ServiceDescriptorProto cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      ServiceDescriptorProto result;

+      

+      private ServiceDescriptorProto PrepareBuilder() {

+        if (builderIsReadOnly) {

+          ServiceDescriptorProto original = result;

+          result = new ServiceDescriptorProto();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      ServiceDescriptorProto result = new ServiceDescriptorProto();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override ServiceDescriptorProto MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new ServiceDescriptorProto();

+        result = DefaultInstance ?? new ServiceDescriptorProto();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -3616,13 +3959,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override ServiceDescriptorProto BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.method_.MakeReadOnly();

-        ServiceDescriptorProto returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -3636,6 +3978,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(ServiceDescriptorProto other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasName) {

           Name = other.Name;

         }

@@ -3654,6 +3997,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -3723,18 +4067,20 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasName = true;

         result.name_ = value;

         return this;

       }

       public Builder ClearName() {

+        PrepareBuilder();

         result.hasName = false;

         result.name_ = "";

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto> MethodList {

-        get { return result.method_; }

+        get { return PrepareBuilder().method_; }

       }

       public int MethodCount {

         get { return result.MethodCount; }

@@ -3744,29 +4090,35 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetMethod(int index, global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.method_[index] = value;

         return this;

       }

       public Builder SetMethod(int index, global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.method_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddMethod(global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.method_.Add(value);

         return this;

       }

       public Builder AddMethod(global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.method_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeMethod(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto> values) {

+        PrepareBuilder();

         result.method_.Add(values);

         return this;

       }

       public Builder ClearMethod() {

+        PrepareBuilder();

         result.method_.Clear();

         return this;

       }

@@ -3780,18 +4132,21 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetOptions(global::Google.ProtocolBuffers.DescriptorProtos.ServiceOptions value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptions = true;

         result.options_ = value;

         return this;

       }

       public Builder SetOptions(global::Google.ProtocolBuffers.DescriptorProtos.ServiceOptions.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptions = true;

         result.options_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptions(global::Google.ProtocolBuffers.DescriptorProtos.ServiceOptions value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptions &&

             result.options_ != global::Google.ProtocolBuffers.DescriptorProtos.ServiceOptions.DefaultInstance) {

             result.options_ = global::Google.ProtocolBuffers.DescriptorProtos.ServiceOptions.CreateBuilder(result.options_).MergeFrom(value).BuildPartial();

@@ -3802,6 +4157,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;

       }

       public Builder ClearOptions() {

+        PrepareBuilder();

         result.hasOptions = false;

         result.options_ = global::Google.ProtocolBuffers.DescriptorProtos.ServiceOptions.DefaultInstance;

         return this;

@@ -3966,7 +4322,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(MethodDescriptorProto prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -3976,21 +4332,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new MethodDescriptorProto();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(MethodDescriptorProto cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      MethodDescriptorProto result;

+      

+      private MethodDescriptorProto PrepareBuilder() {

+        if (builderIsReadOnly) {

+          MethodDescriptorProto original = result;

+          result = new MethodDescriptorProto();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      MethodDescriptorProto result = new MethodDescriptorProto();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override MethodDescriptorProto MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new MethodDescriptorProto();

+        result = DefaultInstance ?? new MethodDescriptorProto();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -4002,12 +4385,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override MethodDescriptorProto BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        MethodDescriptorProto returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -4021,6 +4403,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(MethodDescriptorProto other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasName) {

           Name = other.Name;

         }

@@ -4042,6 +4425,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -4115,11 +4499,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasName = true;

         result.name_ = value;

         return this;

       }

       public Builder ClearName() {

+        PrepareBuilder();

         result.hasName = false;

         result.name_ = "";

         return this;

@@ -4134,11 +4520,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetInputType(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasInputType = true;

         result.inputType_ = value;

         return this;

       }

       public Builder ClearInputType() {

+        PrepareBuilder();

         result.hasInputType = false;

         result.inputType_ = "";

         return this;

@@ -4153,11 +4541,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetOutputType(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOutputType = true;

         result.outputType_ = value;

         return this;

       }

       public Builder ClearOutputType() {

+        PrepareBuilder();

         result.hasOutputType = false;

         result.outputType_ = "";

         return this;

@@ -4172,18 +4562,21 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetOptions(global::Google.ProtocolBuffers.DescriptorProtos.MethodOptions value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptions = true;

         result.options_ = value;

         return this;

       }

       public Builder SetOptions(global::Google.ProtocolBuffers.DescriptorProtos.MethodOptions.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptions = true;

         result.options_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptions(global::Google.ProtocolBuffers.DescriptorProtos.MethodOptions value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptions &&

             result.options_ != global::Google.ProtocolBuffers.DescriptorProtos.MethodOptions.DefaultInstance) {

             result.options_ = global::Google.ProtocolBuffers.DescriptorProtos.MethodOptions.CreateBuilder(result.options_).MergeFrom(value).BuildPartial();

@@ -4194,6 +4587,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;

       }

       public Builder ClearOptions() {

+        PrepareBuilder();

         result.hasOptions = false;

         result.options_ = global::Google.ProtocolBuffers.DescriptorProtos.MethodOptions.DefaultInstance;

         return this;

@@ -4444,7 +4838,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(FileOptions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -4454,21 +4848,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new FileOptions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(FileOptions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      FileOptions result;

       

-      FileOptions result = new FileOptions();

+      private FileOptions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          FileOptions original = result;

+          result = new FileOptions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override FileOptions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new FileOptions();

+        result = DefaultInstance ?? new FileOptions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -4480,13 +4901,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override FileOptions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.uninterpretedOption_.MakeReadOnly();

-        FileOptions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -4500,6 +4920,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(FileOptions other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.FileOptions.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasJavaPackage) {

           JavaPackage = other.JavaPackage;

         }

@@ -4534,6 +4955,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -4626,11 +5048,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetJavaPackage(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasJavaPackage = true;

         result.javaPackage_ = value;

         return this;

       }

       public Builder ClearJavaPackage() {

+        PrepareBuilder();

         result.hasJavaPackage = false;

         result.javaPackage_ = "";

         return this;

@@ -4645,11 +5069,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetJavaOuterClassname(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasJavaOuterClassname = true;

         result.javaOuterClassname_ = value;

         return this;

       }

       public Builder ClearJavaOuterClassname() {

+        PrepareBuilder();

         result.hasJavaOuterClassname = false;

         result.javaOuterClassname_ = "";

         return this;

@@ -4663,11 +5089,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetJavaMultipleFiles(value); }

       }

       public Builder SetJavaMultipleFiles(bool value) {

+        PrepareBuilder();

         result.hasJavaMultipleFiles = true;

         result.javaMultipleFiles_ = value;

         return this;

       }

       public Builder ClearJavaMultipleFiles() {

+        PrepareBuilder();

         result.hasJavaMultipleFiles = false;

         result.javaMultipleFiles_ = false;

         return this;

@@ -4681,11 +5109,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetOptimizeFor(value); }

       }

       public Builder SetOptimizeFor(global::Google.ProtocolBuffers.DescriptorProtos.FileOptions.Types.OptimizeMode value) {

+        PrepareBuilder();

         result.hasOptimizeFor = true;

         result.optimizeFor_ = value;

         return this;

       }

       public Builder ClearOptimizeFor() {

+        PrepareBuilder();

         result.hasOptimizeFor = false;

         result.optimizeFor_ = global::Google.ProtocolBuffers.DescriptorProtos.FileOptions.Types.OptimizeMode.SPEED;

         return this;

@@ -4699,11 +5129,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetCcGenericServices(value); }

       }

       public Builder SetCcGenericServices(bool value) {

+        PrepareBuilder();

         result.hasCcGenericServices = true;

         result.ccGenericServices_ = value;

         return this;

       }

       public Builder ClearCcGenericServices() {

+        PrepareBuilder();

         result.hasCcGenericServices = false;

         result.ccGenericServices_ = true;

         return this;

@@ -4717,11 +5149,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetJavaGenericServices(value); }

       }

       public Builder SetJavaGenericServices(bool value) {

+        PrepareBuilder();

         result.hasJavaGenericServices = true;

         result.javaGenericServices_ = value;

         return this;

       }

       public Builder ClearJavaGenericServices() {

+        PrepareBuilder();

         result.hasJavaGenericServices = false;

         result.javaGenericServices_ = true;

         return this;

@@ -4735,18 +5169,20 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetPyGenericServices(value); }

       }

       public Builder SetPyGenericServices(bool value) {

+        PrepareBuilder();

         result.hasPyGenericServices = true;

         result.pyGenericServices_ = value;

         return this;

       }

       public Builder ClearPyGenericServices() {

+        PrepareBuilder();

         result.hasPyGenericServices = false;

         result.pyGenericServices_ = true;

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption> UninterpretedOptionList {

-        get { return result.uninterpretedOption_; }

+        get { return PrepareBuilder().uninterpretedOption_; }

       }

       public int UninterpretedOptionCount {

         get { return result.UninterpretedOptionCount; }

@@ -4756,29 +5192,35 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetUninterpretedOption(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.uninterpretedOption_[index] = value;

         return this;

       }

       public Builder SetUninterpretedOption(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.uninterpretedOption_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddUninterpretedOption(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.uninterpretedOption_.Add(value);

         return this;

       }

       public Builder AddUninterpretedOption(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.uninterpretedOption_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeUninterpretedOption(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption> values) {

+        PrepareBuilder();

         result.uninterpretedOption_.Add(values);

         return this;

       }

       public Builder ClearUninterpretedOption() {

+        PrepareBuilder();

         result.uninterpretedOption_.Clear();

         return this;

       }

@@ -4932,7 +5374,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(MessageOptions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -4942,21 +5384,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new MessageOptions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(MessageOptions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      MessageOptions result = new MessageOptions();

+      bool builderIsReadOnly;

+      MessageOptions result;

+      

+      private MessageOptions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          MessageOptions original = result;

+          result = new MessageOptions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override MessageOptions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new MessageOptions();

+        result = DefaultInstance ?? new MessageOptions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -4968,13 +5437,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override MessageOptions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.uninterpretedOption_.MakeReadOnly();

-        MessageOptions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -4988,6 +5456,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(MessageOptions other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.MessageOptions.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasMessageSetWireFormat) {

           MessageSetWireFormat = other.MessageSetWireFormat;

         }

@@ -5007,6 +5476,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -5070,11 +5540,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetMessageSetWireFormat(value); }

       }

       public Builder SetMessageSetWireFormat(bool value) {

+        PrepareBuilder();

         result.hasMessageSetWireFormat = true;

         result.messageSetWireFormat_ = value;

         return this;

       }

       public Builder ClearMessageSetWireFormat() {

+        PrepareBuilder();

         result.hasMessageSetWireFormat = false;

         result.messageSetWireFormat_ = false;

         return this;

@@ -5088,18 +5560,20 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetNoStandardDescriptorAccessor(value); }

       }

       public Builder SetNoStandardDescriptorAccessor(bool value) {

+        PrepareBuilder();

         result.hasNoStandardDescriptorAccessor = true;

         result.noStandardDescriptorAccessor_ = value;

         return this;

       }

       public Builder ClearNoStandardDescriptorAccessor() {

+        PrepareBuilder();

         result.hasNoStandardDescriptorAccessor = false;

         result.noStandardDescriptorAccessor_ = false;

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption> UninterpretedOptionList {

-        get { return result.uninterpretedOption_; }

+        get { return PrepareBuilder().uninterpretedOption_; }

       }

       public int UninterpretedOptionCount {

         get { return result.UninterpretedOptionCount; }

@@ -5109,29 +5583,35 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetUninterpretedOption(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.uninterpretedOption_[index] = value;

         return this;

       }

       public Builder SetUninterpretedOption(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.uninterpretedOption_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddUninterpretedOption(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.uninterpretedOption_.Add(value);

         return this;

       }

       public Builder AddUninterpretedOption(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.uninterpretedOption_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeUninterpretedOption(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption> values) {

+        PrepareBuilder();

         result.uninterpretedOption_.Add(values);

         return this;

       }

       public Builder ClearUninterpretedOption() {

+        PrepareBuilder();

         result.uninterpretedOption_.Clear();

         return this;

       }

@@ -5333,7 +5813,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(FieldOptions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -5343,21 +5823,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new FieldOptions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(FieldOptions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      FieldOptions result = new FieldOptions();

+      bool builderIsReadOnly;

+      FieldOptions result;

+      

+      private FieldOptions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          FieldOptions original = result;

+          result = new FieldOptions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override FieldOptions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new FieldOptions();

+        result = DefaultInstance ?? new FieldOptions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -5369,13 +5876,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override FieldOptions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.uninterpretedOption_.MakeReadOnly();

-        FieldOptions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -5389,6 +5895,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(FieldOptions other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.FieldOptions.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasCtype) {

           Ctype = other.Ctype;

         }

@@ -5414,6 +5921,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -5493,11 +6001,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetCtype(value); }

       }

       public Builder SetCtype(global::Google.ProtocolBuffers.DescriptorProtos.FieldOptions.Types.CType value) {

+        PrepareBuilder();

         result.hasCtype = true;

         result.ctype_ = value;

         return this;

       }

       public Builder ClearCtype() {

+        PrepareBuilder();

         result.hasCtype = false;

         result.ctype_ = global::Google.ProtocolBuffers.DescriptorProtos.FieldOptions.Types.CType.STRING;

         return this;

@@ -5511,11 +6021,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetPacked(value); }

       }

       public Builder SetPacked(bool value) {

+        PrepareBuilder();

         result.hasPacked = true;

         result.packed_ = value;

         return this;

       }

       public Builder ClearPacked() {

+        PrepareBuilder();

         result.hasPacked = false;

         result.packed_ = false;

         return this;

@@ -5529,11 +6041,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetDeprecated(value); }

       }

       public Builder SetDeprecated(bool value) {

+        PrepareBuilder();

         result.hasDeprecated = true;

         result.deprecated_ = value;

         return this;

       }

       public Builder ClearDeprecated() {

+        PrepareBuilder();

         result.hasDeprecated = false;

         result.deprecated_ = false;

         return this;

@@ -5548,18 +6062,20 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetExperimentalMapKey(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasExperimentalMapKey = true;

         result.experimentalMapKey_ = value;

         return this;

       }

       public Builder ClearExperimentalMapKey() {

+        PrepareBuilder();

         result.hasExperimentalMapKey = false;

         result.experimentalMapKey_ = "";

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption> UninterpretedOptionList {

-        get { return result.uninterpretedOption_; }

+        get { return PrepareBuilder().uninterpretedOption_; }

       }

       public int UninterpretedOptionCount {

         get { return result.UninterpretedOptionCount; }

@@ -5569,29 +6085,35 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetUninterpretedOption(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.uninterpretedOption_[index] = value;

         return this;

       }

       public Builder SetUninterpretedOption(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.uninterpretedOption_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddUninterpretedOption(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.uninterpretedOption_.Add(value);

         return this;

       }

       public Builder AddUninterpretedOption(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.uninterpretedOption_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeUninterpretedOption(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption> values) {

+        PrepareBuilder();

         result.uninterpretedOption_.Add(values);

         return this;

       }

       public Builder ClearUninterpretedOption() {

+        PrepareBuilder();

         result.uninterpretedOption_.Clear();

         return this;

       }

@@ -5713,7 +6235,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(EnumOptions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -5723,21 +6245,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new EnumOptions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(EnumOptions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      EnumOptions result;

+      

+      private EnumOptions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          EnumOptions original = result;

+          result = new EnumOptions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      EnumOptions result = new EnumOptions();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override EnumOptions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new EnumOptions();

+        result = DefaultInstance ?? new EnumOptions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -5749,13 +6298,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override EnumOptions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.uninterpretedOption_.MakeReadOnly();

-        EnumOptions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -5769,6 +6317,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(EnumOptions other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.EnumOptions.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.uninterpretedOption_.Count != 0) {

           result.uninterpretedOption_.Add(other.uninterpretedOption_);

         }

@@ -5782,6 +6331,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -5830,7 +6380,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption> UninterpretedOptionList {

-        get { return result.uninterpretedOption_; }

+        get { return PrepareBuilder().uninterpretedOption_; }

       }

       public int UninterpretedOptionCount {

         get { return result.UninterpretedOptionCount; }

@@ -5840,29 +6390,35 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetUninterpretedOption(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.uninterpretedOption_[index] = value;

         return this;

       }

       public Builder SetUninterpretedOption(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.uninterpretedOption_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddUninterpretedOption(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.uninterpretedOption_.Add(value);

         return this;

       }

       public Builder AddUninterpretedOption(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.uninterpretedOption_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeUninterpretedOption(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption> values) {

+        PrepareBuilder();

         result.uninterpretedOption_.Add(values);

         return this;

       }

       public Builder ClearUninterpretedOption() {

+        PrepareBuilder();

         result.uninterpretedOption_.Clear();

         return this;

       }

@@ -5984,7 +6540,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(EnumValueOptions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -5994,21 +6550,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new EnumValueOptions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(EnumValueOptions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      EnumValueOptions result;

       

-      EnumValueOptions result = new EnumValueOptions();

+      private EnumValueOptions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          EnumValueOptions original = result;

+          result = new EnumValueOptions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override EnumValueOptions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new EnumValueOptions();

+        result = DefaultInstance ?? new EnumValueOptions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -6020,13 +6603,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override EnumValueOptions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.uninterpretedOption_.MakeReadOnly();

-        EnumValueOptions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -6040,6 +6622,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(EnumValueOptions other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.EnumValueOptions.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.uninterpretedOption_.Count != 0) {

           result.uninterpretedOption_.Add(other.uninterpretedOption_);

         }

@@ -6053,6 +6636,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -6101,7 +6685,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption> UninterpretedOptionList {

-        get { return result.uninterpretedOption_; }

+        get { return PrepareBuilder().uninterpretedOption_; }

       }

       public int UninterpretedOptionCount {

         get { return result.UninterpretedOptionCount; }

@@ -6111,29 +6695,35 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetUninterpretedOption(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.uninterpretedOption_[index] = value;

         return this;

       }

       public Builder SetUninterpretedOption(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.uninterpretedOption_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddUninterpretedOption(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.uninterpretedOption_.Add(value);

         return this;

       }

       public Builder AddUninterpretedOption(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.uninterpretedOption_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeUninterpretedOption(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption> values) {

+        PrepareBuilder();

         result.uninterpretedOption_.Add(values);

         return this;

       }

       public Builder ClearUninterpretedOption() {

+        PrepareBuilder();

         result.uninterpretedOption_.Clear();

         return this;

       }

@@ -6255,7 +6845,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(ServiceOptions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -6265,21 +6855,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new ServiceOptions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(ServiceOptions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      ServiceOptions result;

+      

+      private ServiceOptions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          ServiceOptions original = result;

+          result = new ServiceOptions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      ServiceOptions result = new ServiceOptions();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override ServiceOptions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new ServiceOptions();

+        result = DefaultInstance ?? new ServiceOptions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -6291,13 +6908,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override ServiceOptions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.uninterpretedOption_.MakeReadOnly();

-        ServiceOptions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -6311,6 +6927,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(ServiceOptions other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.ServiceOptions.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.uninterpretedOption_.Count != 0) {

           result.uninterpretedOption_.Add(other.uninterpretedOption_);

         }

@@ -6324,6 +6941,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -6372,7 +6990,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption> UninterpretedOptionList {

-        get { return result.uninterpretedOption_; }

+        get { return PrepareBuilder().uninterpretedOption_; }

       }

       public int UninterpretedOptionCount {

         get { return result.UninterpretedOptionCount; }

@@ -6382,29 +7000,35 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetUninterpretedOption(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.uninterpretedOption_[index] = value;

         return this;

       }

       public Builder SetUninterpretedOption(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.uninterpretedOption_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddUninterpretedOption(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.uninterpretedOption_.Add(value);

         return this;

       }

       public Builder AddUninterpretedOption(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.uninterpretedOption_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeUninterpretedOption(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption> values) {

+        PrepareBuilder();

         result.uninterpretedOption_.Add(values);

         return this;

       }

       public Builder ClearUninterpretedOption() {

+        PrepareBuilder();

         result.uninterpretedOption_.Clear();

         return this;

       }

@@ -6526,7 +7150,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(MethodOptions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -6536,21 +7160,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new MethodOptions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(MethodOptions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      MethodOptions result = new MethodOptions();

+      bool builderIsReadOnly;

+      MethodOptions result;

+      

+      private MethodOptions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          MethodOptions original = result;

+          result = new MethodOptions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override MethodOptions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new MethodOptions();

+        result = DefaultInstance ?? new MethodOptions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -6562,13 +7213,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override MethodOptions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.uninterpretedOption_.MakeReadOnly();

-        MethodOptions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -6582,6 +7232,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(MethodOptions other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.MethodOptions.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.uninterpretedOption_.Count != 0) {

           result.uninterpretedOption_.Add(other.uninterpretedOption_);

         }

@@ -6595,6 +7246,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -6643,7 +7295,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption> UninterpretedOptionList {

-        get { return result.uninterpretedOption_; }

+        get { return PrepareBuilder().uninterpretedOption_; }

       }

       public int UninterpretedOptionCount {

         get { return result.UninterpretedOptionCount; }

@@ -6653,29 +7305,35 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetUninterpretedOption(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.uninterpretedOption_[index] = value;

         return this;

       }

       public Builder SetUninterpretedOption(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.uninterpretedOption_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddUninterpretedOption(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.uninterpretedOption_.Add(value);

         return this;

       }

       public Builder AddUninterpretedOption(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.uninterpretedOption_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeUninterpretedOption(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption> values) {

+        PrepareBuilder();

         result.uninterpretedOption_.Add(values);

         return this;

       }

       public Builder ClearUninterpretedOption() {

+        PrepareBuilder();

         result.uninterpretedOption_.Clear();

         return this;

       }

@@ -6839,7 +7497,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(NamePart prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -6849,21 +7507,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new NamePart();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(NamePart cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          NamePart result;

+          

+          private NamePart PrepareBuilder() {

+            if (builderIsReadOnly) {

+              NamePart original = result;

+              result = new NamePart();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

           

-          NamePart result = new NamePart();

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override NamePart MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new NamePart();

+            result = DefaultInstance ?? new NamePart();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -6875,12 +7560,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           }

           

           public override NamePart BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            NamePart returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -6894,6 +7578,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           

           public override Builder MergeFrom(NamePart other) {

             if (other == global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Types.NamePart.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasNamePart_) {

               NamePart_ = other.NamePart_;

             }

@@ -6909,6 +7594,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -6969,11 +7655,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           }

           public Builder SetNamePart_(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasNamePart_ = true;

             result.namePart_ = value;

             return this;

           }

           public Builder ClearNamePart_() {

+            PrepareBuilder();

             result.hasNamePart_ = false;

             result.namePart_ = "";

             return this;

@@ -6987,11 +7675,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
             set { SetIsExtension(value); }

           }

           public Builder SetIsExtension(bool value) {

+            PrepareBuilder();

             result.hasIsExtension = true;

             result.isExtension_ = value;

             return this;

           }

           public Builder ClearIsExtension() {

+            PrepareBuilder();

             result.hasIsExtension = false;

             result.isExtension_ = false;

             return this;

@@ -7166,7 +7856,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(UninterpretedOption prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -7176,21 +7866,48 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new UninterpretedOption();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(UninterpretedOption cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      UninterpretedOption result;

+      

+      private UninterpretedOption PrepareBuilder() {

+        if (builderIsReadOnly) {

+          UninterpretedOption original = result;

+          result = new UninterpretedOption();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      UninterpretedOption result = new UninterpretedOption();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override UninterpretedOption MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new UninterpretedOption();

+        result = DefaultInstance ?? new UninterpretedOption();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -7202,13 +7919,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override UninterpretedOption BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.name_.MakeReadOnly();

-        UninterpretedOption returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -7222,6 +7938,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       public override Builder MergeFrom(UninterpretedOption other) {

         if (other == global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.name_.Count != 0) {

           result.name_.Add(other.name_);

         }

@@ -7249,6 +7966,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -7317,7 +8035,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Types.NamePart> NameList {

-        get { return result.name_; }

+        get { return PrepareBuilder().name_; }

       }

       public int NameCount {

         get { return result.NameCount; }

@@ -7327,29 +8045,35 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetName(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Types.NamePart value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.name_[index] = value;

         return this;

       }

       public Builder SetName(int index, global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Types.NamePart.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.name_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddName(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Types.NamePart value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.name_.Add(value);

         return this;

       }

       public Builder AddName(global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Types.NamePart.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.name_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeName(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.UninterpretedOption.Types.NamePart> values) {

+        PrepareBuilder();

         result.name_.Add(values);

         return this;

       }

       public Builder ClearName() {

+        PrepareBuilder();

         result.name_.Clear();

         return this;

       }

@@ -7363,11 +8087,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetIdentifierValue(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasIdentifierValue = true;

         result.identifierValue_ = value;

         return this;

       }

       public Builder ClearIdentifierValue() {

+        PrepareBuilder();

         result.hasIdentifierValue = false;

         result.identifierValue_ = "";

         return this;

@@ -7383,11 +8109,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetPositiveIntValue(ulong value) {

+        PrepareBuilder();

         result.hasPositiveIntValue = true;

         result.positiveIntValue_ = value;

         return this;

       }

       public Builder ClearPositiveIntValue() {

+        PrepareBuilder();

         result.hasPositiveIntValue = false;

         result.positiveIntValue_ = 0UL;

         return this;

@@ -7401,11 +8129,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetNegativeIntValue(value); }

       }

       public Builder SetNegativeIntValue(long value) {

+        PrepareBuilder();

         result.hasNegativeIntValue = true;

         result.negativeIntValue_ = value;

         return this;

       }

       public Builder ClearNegativeIntValue() {

+        PrepareBuilder();

         result.hasNegativeIntValue = false;

         result.negativeIntValue_ = 0L;

         return this;

@@ -7419,11 +8149,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         set { SetDoubleValue(value); }

       }

       public Builder SetDoubleValue(double value) {

+        PrepareBuilder();

         result.hasDoubleValue = true;

         result.doubleValue_ = value;

         return this;

       }

       public Builder ClearDoubleValue() {

+        PrepareBuilder();

         result.hasDoubleValue = false;

         result.doubleValue_ = 0D;

         return this;

@@ -7438,11 +8170,13 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }

       public Builder SetStringValue(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasStringValue = true;

         result.stringValue_ = value;

         return this;

       }

       public Builder ClearStringValue() {

+        PrepareBuilder();

         result.hasStringValue = false;

         result.stringValue_ = pb::ByteString.Empty;

         return this;

diff --git a/src/ProtocolBuffers/GeneratedBuilder.cs b/src/ProtocolBuffers/GeneratedBuilder.cs
index a56be42e..fd6fe4d7 100644
--- a/src/ProtocolBuffers/GeneratedBuilder.cs
+++ b/src/ProtocolBuffers/GeneratedBuilder.cs
@@ -58,12 +58,7 @@ namespace Google.ProtocolBuffers
 

         protected internal FieldAccessorTable<TMessage, TBuilder> InternalFieldAccessors

         {

-            get { return MessageBeingBuilt.FieldAccessorsFromBuilder; }

-        }

-

-        public override bool IsInitialized

-        {

-            get { return MessageBeingBuilt.IsInitialized; }

+            get { return DefaultInstanceForType.FieldAccessorsFromBuilder; }

         }

 

         public override IDictionary<FieldDescriptor, object> AllFields

@@ -97,7 +92,7 @@ namespace Google.ProtocolBuffers
 

         public override MessageDescriptor DescriptorForType

         {

-            get { return MessageBeingBuilt.DescriptorForType; }

+            get { return DefaultInstanceForType.DescriptorForType; }

         }

 

         public override int GetRepeatedFieldCount(FieldDescriptor field)

@@ -204,7 +199,7 @@ namespace Google.ProtocolBuffers
         public override TMessage Build()

         {

             // If the message is null, we'll throw a more appropriate exception in BuildPartial.

-            if (MessageBeingBuilt != null && !IsInitialized)

+            if (!IsInitialized)

             {

                 throw new UninitializedMessageException(MessageBeingBuilt);

             }

diff --git a/src/ProtocolBuffers/GeneratedBuilderLite.cs b/src/ProtocolBuffers/GeneratedBuilderLite.cs
index a5f7f891..4030e801 100644
--- a/src/ProtocolBuffers/GeneratedBuilderLite.cs
+++ b/src/ProtocolBuffers/GeneratedBuilderLite.cs
@@ -61,11 +61,6 @@ namespace Google.ProtocolBuffers
 

         public abstract TBuilder MergeFrom(TMessage other);

 

-        public override bool IsInitialized

-        {

-            get { return MessageBeingBuilt.IsInitialized; }

-        }

-

         /// <summary>

         /// Called by derived classes to parse an unknown field.

         /// </summary>

@@ -96,7 +91,7 @@ namespace Google.ProtocolBuffers
         public override TMessage Build()

         {

             // If the message is null, we'll throw a more appropriate exception in BuildPartial.

-            if (MessageBeingBuilt != null && !IsInitialized)

+            if (!IsInitialized)

             {

                 throw new UninitializedMessageException(MessageBeingBuilt);

             }

diff --git a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasFullProtoFile.cs b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasFullProtoFile.cs
index 9119e4e9..260e6397 100644
--- a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasFullProtoFile.cs
+++ b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasFullProtoFile.cs
@@ -243,7 +243,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(PhoneNumber prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -253,21 +253,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new PhoneNumber();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(PhoneNumber cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          PhoneNumber result;

           

-          PhoneNumber result = new PhoneNumber();

+          private PhoneNumber PrepareBuilder() {

+            if (builderIsReadOnly) {

+              PhoneNumber original = result;

+              result = new PhoneNumber();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override PhoneNumber MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new PhoneNumber();

+            result = DefaultInstance ?? new PhoneNumber();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -279,12 +306,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override PhoneNumber BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            PhoneNumber returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           

@@ -297,11 +323,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetNumber(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasNumber = true;

             result.number_ = value;

             return this;

           }

           public Builder ClearNumber() {

+            PrepareBuilder();

             result.hasNumber = false;

             result.number_ = "";

             return this;

@@ -315,11 +343,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetType(value); }

           }

           public Builder SetType(global::Google.ProtocolBuffers.TestProtos.TestInteropPerson.Types.PhoneType value) {

+            PrepareBuilder();

             result.hasType = true;

             result.type_ = value;

             return this;

           }

           public Builder ClearType() {

+            PrepareBuilder();

             result.hasType = false;

             result.type_ = global::Google.ProtocolBuffers.TestProtos.TestInteropPerson.Types.PhoneType.HOME;

             return this;

@@ -441,7 +471,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(Addresses prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -451,21 +481,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new Addresses();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(Addresses cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          Addresses result;

+          

+          private Addresses PrepareBuilder() {

+            if (builderIsReadOnly) {

+              Addresses original = result;

+              result = new Addresses();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

           

-          Addresses result = new Addresses();

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override Addresses MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new Addresses();

+            result = DefaultInstance ?? new Addresses();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -477,12 +534,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Addresses BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            Addresses returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           

@@ -495,11 +551,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetAddress(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasAddress = true;

             result.address_ = value;

             return this;

           }

           public Builder ClearAddress() {

+            PrepareBuilder();

             result.hasAddress = false;

             result.address_ = "";

             return this;

@@ -514,11 +572,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetAddress2(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasAddress2 = true;

             result.address2_ = value;

             return this;

           }

           public Builder ClearAddress2() {

+            PrepareBuilder();

             result.hasAddress2 = false;

             result.address2_ = "";

             return this;

@@ -533,11 +593,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetCity(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasCity = true;

             result.city_ = value;

             return this;

           }

           public Builder ClearCity() {

+            PrepareBuilder();

             result.hasCity = false;

             result.city_ = "";

             return this;

@@ -552,11 +614,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetState(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasState = true;

             result.state_ = value;

             return this;

           }

           public Builder ClearState() {

+            PrepareBuilder();

             result.hasState = false;

             result.state_ = "";

             return this;

@@ -572,11 +636,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           [global::System.CLSCompliant(false)]

           public Builder SetZip(uint value) {

+            PrepareBuilder();

             result.hasZip = true;

             result.zip_ = value;

             return this;

           }

           public Builder ClearZip() {

+            PrepareBuilder();

             result.hasZip = false;

             result.zip_ = 0;

             return this;

@@ -690,7 +756,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestInteropPerson prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -700,21 +766,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestInteropPerson();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestInteropPerson cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestInteropPerson result = new TestInteropPerson();

+      bool builderIsReadOnly;

+      TestInteropPerson result;

+      

+      private TestInteropPerson PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestInteropPerson original = result;

+          result = new TestInteropPerson();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestInteropPerson MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestInteropPerson();

+        result = DefaultInstance ?? new TestInteropPerson();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -726,15 +819,14 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestInteropPerson BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.codes_.MakeReadOnly();

         result.phone_.MakeReadOnly();

         result.addresses_.MakeReadOnly();

-        TestInteropPerson returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       

@@ -747,11 +839,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasName = true;

         result.name_ = value;

         return this;

       }

       public Builder ClearName() {

+        PrepareBuilder();

         result.hasName = false;

         result.name_ = "";

         return this;

@@ -765,11 +859,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetId(value); }

       }

       public Builder SetId(int value) {

+        PrepareBuilder();

         result.hasId = true;

         result.id_ = value;

         return this;

       }

       public Builder ClearId() {

+        PrepareBuilder();

         result.hasId = false;

         result.id_ = 0;

         return this;

@@ -784,18 +880,20 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetEmail(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasEmail = true;

         result.email_ = value;

         return this;

       }

       public Builder ClearEmail() {

+        PrepareBuilder();

         result.hasEmail = false;

         result.email_ = "";

         return this;

       }

       

       public pbc::IPopsicleList<int> CodesList {

-        get { return result.codes_; }

+        get { return PrepareBuilder().codes_; }

       }

       public int CodesCount {

         get { return result.CodesCount; }

@@ -804,24 +902,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetCodes(index);

       }

       public Builder SetCodes(int index, int value) {

+        PrepareBuilder();

         result.codes_[index] = value;

         return this;

       }

       public Builder AddCodes(int value) {

+        PrepareBuilder();

         result.codes_.Add(value);

         return this;

       }

       public Builder AddRangeCodes(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.codes_.Add(values);

         return this;

       }

       public Builder ClearCodes() {

+        PrepareBuilder();

         result.codes_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestInteropPerson.Types.PhoneNumber> PhoneList {

-        get { return result.phone_; }

+        get { return PrepareBuilder().phone_; }

       }

       public int PhoneCount {

         get { return result.PhoneCount; }

@@ -831,35 +933,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetPhone(int index, global::Google.ProtocolBuffers.TestProtos.TestInteropPerson.Types.PhoneNumber value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.phone_[index] = value;

         return this;

       }

       public Builder SetPhone(int index, global::Google.ProtocolBuffers.TestProtos.TestInteropPerson.Types.PhoneNumber.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.phone_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddPhone(global::Google.ProtocolBuffers.TestProtos.TestInteropPerson.Types.PhoneNumber value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.phone_.Add(value);

         return this;

       }

       public Builder AddPhone(global::Google.ProtocolBuffers.TestProtos.TestInteropPerson.Types.PhoneNumber.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.phone_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangePhone(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestInteropPerson.Types.PhoneNumber> values) {

+        PrepareBuilder();

         result.phone_.Add(values);

         return this;

       }

       public Builder ClearPhone() {

+        PrepareBuilder();

         result.phone_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestInteropPerson.Types.Addresses> AddressesList {

-        get { return result.addresses_; }

+        get { return PrepareBuilder().addresses_; }

       }

       public int AddressesCount {

         get { return result.AddressesCount; }

@@ -869,29 +977,35 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetAddresses(int index, global::Google.ProtocolBuffers.TestProtos.TestInteropPerson.Types.Addresses value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.addresses_[index] = value;

         return this;

       }

       public Builder SetAddresses(int index, global::Google.ProtocolBuffers.TestProtos.TestInteropPerson.Types.Addresses.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.addresses_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddAddresses(global::Google.ProtocolBuffers.TestProtos.TestInteropPerson.Types.Addresses value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.addresses_.Add(value);

         return this;

       }

       public Builder AddAddresses(global::Google.ProtocolBuffers.TestProtos.TestInteropPerson.Types.Addresses.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.addresses_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeAddresses(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestInteropPerson.Types.Addresses> values) {

+        PrepareBuilder();

         result.addresses_.Add(values);

         return this;

       }

       public Builder ClearAddresses() {

+        PrepareBuilder();

         result.addresses_.Clear();

         return this;

       }

@@ -971,7 +1085,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestInteropEmployeeId prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -981,21 +1095,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestInteropEmployeeId();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestInteropEmployeeId cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestInteropEmployeeId result;

+      

+      private TestInteropEmployeeId PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestInteropEmployeeId original = result;

+          result = new TestInteropEmployeeId();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestInteropEmployeeId result = new TestInteropEmployeeId();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestInteropEmployeeId MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestInteropEmployeeId();

+        result = DefaultInstance ?? new TestInteropEmployeeId();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1007,12 +1148,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestInteropEmployeeId BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestInteropEmployeeId returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       

@@ -1025,11 +1165,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetNumber(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasNumber = true;

         result.number_ = value;

         return this;

       }

       public Builder ClearNumber() {

+        PrepareBuilder();

         result.hasNumber = false;

         result.number_ = "";

         return this;

@@ -1153,7 +1295,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(SubA prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1163,21 +1305,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new SubA();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(SubA cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          SubA result;

           

-          SubA result = new SubA();

+          private SubA PrepareBuilder() {

+            if (builderIsReadOnly) {

+              SubA original = result;

+              result = new SubA();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override SubA MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new SubA();

+            result = DefaultInstance ?? new SubA();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -1189,13 +1358,12 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override SubA BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

             result.values_.MakeReadOnly();

-            SubA returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           

@@ -1207,18 +1375,20 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetCount(value); }

           }

           public Builder SetCount(int value) {

+            PrepareBuilder();

             result.hasCount = true;

             result.count_ = value;

             return this;

           }

           public Builder ClearCount() {

+            PrepareBuilder();

             result.hasCount = false;

             result.count_ = 0;

             return this;

           }

           

           public pbc::IPopsicleList<string> ValuesList {

-            get { return result.values_; }

+            get { return PrepareBuilder().values_; }

           }

           public int ValuesCount {

             get { return result.ValuesCount; }

@@ -1228,19 +1398,23 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetValues(int index, string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.values_[index] = value;

             return this;

           }

           public Builder AddValues(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.values_.Add(value);

             return this;

           }

           public Builder AddRangeValues(scg::IEnumerable<string> values) {

+            PrepareBuilder();

             result.values_.Add(values);

             return this;

           }

           public Builder ClearValues() {

+            PrepareBuilder();

             result.values_.Clear();

             return this;

           }

@@ -1327,7 +1501,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestMissingFieldsA prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1337,21 +1511,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestMissingFieldsA();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestMissingFieldsA cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestMissingFieldsA result;

+      

+      private TestMissingFieldsA PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestMissingFieldsA original = result;

+          result = new TestMissingFieldsA();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestMissingFieldsA result = new TestMissingFieldsA();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestMissingFieldsA MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestMissingFieldsA();

+        result = DefaultInstance ?? new TestMissingFieldsA();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1363,12 +1564,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestMissingFieldsA BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestMissingFieldsA returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       

@@ -1381,11 +1581,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasName = true;

         result.name_ = value;

         return this;

       }

       public Builder ClearName() {

+        PrepareBuilder();

         result.hasName = false;

         result.name_ = "";

         return this;

@@ -1399,11 +1601,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetId(value); }

       }

       public Builder SetId(int value) {

+        PrepareBuilder();

         result.hasId = true;

         result.id_ = value;

         return this;

       }

       public Builder ClearId() {

+        PrepareBuilder();

         result.hasId = false;

         result.id_ = 0;

         return this;

@@ -1418,11 +1622,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetEmail(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasEmail = true;

         result.email_ = value;

         return this;

       }

       public Builder ClearEmail() {

+        PrepareBuilder();

         result.hasEmail = false;

         result.email_ = "";

         return this;

@@ -1437,18 +1643,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetTestA(global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsA.Types.SubA value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasTestA = true;

         result.testA_ = value;

         return this;

       }

       public Builder SetTestA(global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsA.Types.SubA.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasTestA = true;

         result.testA_ = builderForValue.Build();

         return this;

       }

       public Builder MergeTestA(global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsA.Types.SubA value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasTestA &&

             result.testA_ != global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsA.Types.SubA.DefaultInstance) {

             result.testA_ = global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsA.Types.SubA.CreateBuilder(result.testA_).MergeFrom(value).BuildPartial();

@@ -1459,6 +1668,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearTestA() {

+        PrepareBuilder();

         result.hasTestA = false;

         result.testA_ = global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsA.Types.SubA.DefaultInstance;

         return this;

@@ -1572,7 +1782,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(SubB prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1582,21 +1792,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new SubB();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(SubB cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          SubB result;

           

-          SubB result = new SubB();

+          private SubB PrepareBuilder() {

+            if (builderIsReadOnly) {

+              SubB original = result;

+              result = new SubB();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override SubB MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new SubB();

+            result = DefaultInstance ?? new SubB();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -1608,18 +1845,17 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override SubB BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

             result.values_.MakeReadOnly();

-            SubB returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           

           public pbc::IPopsicleList<string> ValuesList {

-            get { return result.values_; }

+            get { return PrepareBuilder().values_; }

           }

           public int ValuesCount {

             get { return result.ValuesCount; }

@@ -1629,19 +1865,23 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetValues(int index, string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.values_[index] = value;

             return this;

           }

           public Builder AddValues(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.values_.Add(value);

             return this;

           }

           public Builder AddRangeValues(scg::IEnumerable<string> values) {

+            PrepareBuilder();

             result.values_.Add(values);

             return this;

           }

           public Builder ClearValues() {

+            PrepareBuilder();

             result.values_.Clear();

             return this;

           }

@@ -1728,7 +1968,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestMissingFieldsB prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1738,21 +1978,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestMissingFieldsB();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestMissingFieldsB cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestMissingFieldsB result;

+      

+      private TestMissingFieldsB PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestMissingFieldsB original = result;

+          result = new TestMissingFieldsB();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestMissingFieldsB result = new TestMissingFieldsB();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestMissingFieldsB MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestMissingFieldsB();

+        result = DefaultInstance ?? new TestMissingFieldsB();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -1764,12 +2031,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestMissingFieldsB BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestMissingFieldsB returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       

@@ -1782,11 +2048,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasName = true;

         result.name_ = value;

         return this;

       }

       public Builder ClearName() {

+        PrepareBuilder();

         result.hasName = false;

         result.name_ = "";

         return this;

@@ -1800,11 +2068,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetId(value); }

       }

       public Builder SetId(int value) {

+        PrepareBuilder();

         result.hasId = true;

         result.id_ = value;

         return this;

       }

       public Builder ClearId() {

+        PrepareBuilder();

         result.hasId = false;

         result.id_ = 0;

         return this;

@@ -1819,11 +2089,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetWebsite(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasWebsite = true;

         result.website_ = value;

         return this;

       }

       public Builder ClearWebsite() {

+        PrepareBuilder();

         result.hasWebsite = false;

         result.website_ = "";

         return this;

@@ -1838,18 +2110,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetTestB(global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsB.Types.SubB value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasTestB = true;

         result.testB_ = value;

         return this;

       }

       public Builder SetTestB(global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsB.Types.SubB.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasTestB = true;

         result.testB_ = builderForValue.Build();

         return this;

       }

       public Builder MergeTestB(global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsB.Types.SubB value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasTestB &&

             result.testB_ != global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsB.Types.SubB.DefaultInstance) {

             result.testB_ = global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsB.Types.SubB.CreateBuilder(result.testB_).MergeFrom(value).BuildPartial();

@@ -1860,6 +2135,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearTestB() {

+        PrepareBuilder();

         result.hasTestB = false;

         result.testB_ = global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsB.Types.SubB.DefaultInstance;

         return this;

diff --git a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasLiteProtoFile.cs b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasLiteProtoFile.cs
index 07de8a6f..550bc012 100644
--- a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasLiteProtoFile.cs
+++ b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasLiteProtoFile.cs
@@ -189,7 +189,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestRequiredLite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.SerializableAttribute()]

@@ -200,21 +200,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestRequiredLite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestRequiredLite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestRequiredLite result;

+      

+      private TestRequiredLite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestRequiredLite original = result;

+          result = new TestRequiredLite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestRequiredLite result = new TestRequiredLite();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestRequiredLite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestRequiredLite();

+        result = DefaultInstance ?? new TestRequiredLite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override TestRequiredLite DefaultInstanceForType {

@@ -222,12 +249,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestRequiredLite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestRequiredLite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -241,6 +267,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestRequiredLite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestRequiredLite.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasD) {

           D = other.D;

         }

@@ -255,6 +282,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -305,11 +333,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetD(value); }

       }

       public Builder SetD(int value) {

+        PrepareBuilder();

         result.hasD = true;

         result.d_ = value;

         return this;

       }

       public Builder ClearD() {

+        PrepareBuilder();

         result.hasD = false;

         result.d_ = 0;

         return this;

@@ -323,11 +353,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetEn(value); }

       }

       public Builder SetEn(global::Google.ProtocolBuffers.TestProtos.ExtraEnum value) {

+        PrepareBuilder();

         result.hasEn = true;

         result.en_ = value;

         return this;

       }

       public Builder ClearEn() {

+        PrepareBuilder();

         result.hasEn = false;

         result.en_ = global::Google.ProtocolBuffers.TestProtos.ExtraEnum.DEFAULT;

         return this;

@@ -505,7 +537,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(PhoneNumber prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.SerializableAttribute()]

@@ -516,21 +548,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new PhoneNumber();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(PhoneNumber cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

           

-          PhoneNumber result = new PhoneNumber();

+          bool builderIsReadOnly;

+          PhoneNumber result;

+          

+          private PhoneNumber PrepareBuilder() {

+            if (builderIsReadOnly) {

+              PhoneNumber original = result;

+              result = new PhoneNumber();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override PhoneNumber MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new PhoneNumber();

+            result = DefaultInstance ?? new PhoneNumber();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override PhoneNumber DefaultInstanceForType {

@@ -538,12 +597,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override PhoneNumber BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            PhoneNumber returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessageLite other) {

@@ -557,6 +615,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(PhoneNumber other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.PhoneNumber.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasNumber) {

               Number = other.Number;

             }

@@ -571,6 +630,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             uint tag;

             string field_name;

             while (input.ReadTag(out tag, out field_name)) {

@@ -622,11 +682,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetNumber(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasNumber = true;

             result.number_ = value;

             return this;

           }

           public Builder ClearNumber() {

+            PrepareBuilder();

             result.hasNumber = false;

             result.number_ = "";

             return this;

@@ -640,11 +702,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetType(value); }

           }

           public Builder SetType(global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.PhoneType value) {

+            PrepareBuilder();

             result.hasType = true;

             result.type_ = value;

             return this;

           }

           public Builder ClearType() {

+            PrepareBuilder();

             result.hasType = false;

             result.type_ = global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.PhoneType.HOME;

             return this;

@@ -849,7 +913,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(Addresses prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.SerializableAttribute()]

@@ -860,21 +924,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new Addresses();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(Addresses cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          Addresses result;

           

-          Addresses result = new Addresses();

+          private Addresses PrepareBuilder() {

+            if (builderIsReadOnly) {

+              Addresses original = result;

+              result = new Addresses();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override Addresses MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new Addresses();

+            result = DefaultInstance ?? new Addresses();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override Addresses DefaultInstanceForType {

@@ -882,12 +973,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Addresses BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            Addresses returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessageLite other) {

@@ -901,6 +991,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(Addresses other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.Addresses.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasAddress) {

               Address = other.Address;

             }

@@ -924,6 +1015,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             uint tag;

             string field_name;

             while (input.ReadTag(out tag, out field_name)) {

@@ -983,11 +1075,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetAddress(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasAddress = true;

             result.address_ = value;

             return this;

           }

           public Builder ClearAddress() {

+            PrepareBuilder();

             result.hasAddress = false;

             result.address_ = "";

             return this;

@@ -1002,11 +1096,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetAddress2(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasAddress2 = true;

             result.address2_ = value;

             return this;

           }

           public Builder ClearAddress2() {

+            PrepareBuilder();

             result.hasAddress2 = false;

             result.address2_ = "";

             return this;

@@ -1021,11 +1117,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetCity(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasCity = true;

             result.city_ = value;

             return this;

           }

           public Builder ClearCity() {

+            PrepareBuilder();

             result.hasCity = false;

             result.city_ = "";

             return this;

@@ -1040,11 +1138,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetState(string value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.hasState = true;

             result.state_ = value;

             return this;

           }

           public Builder ClearState() {

+            PrepareBuilder();

             result.hasState = false;

             result.state_ = "";

             return this;

@@ -1060,11 +1160,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           [global::System.CLSCompliant(false)]

           public Builder SetZip(uint value) {

+            PrepareBuilder();

             result.hasZip = true;

             result.zip_ = value;

             return this;

           }

           public Builder ClearZip() {

+            PrepareBuilder();

             result.hasZip = false;

             result.zip_ = 0;

             return this;

@@ -1301,7 +1403,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestInteropPersonLite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.SerializableAttribute()]

@@ -1312,21 +1414,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestInteropPersonLite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestInteropPersonLite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestInteropPersonLite result = new TestInteropPersonLite();

+      bool builderIsReadOnly;

+      TestInteropPersonLite result;

+      

+      private TestInteropPersonLite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestInteropPersonLite original = result;

+          result = new TestInteropPersonLite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestInteropPersonLite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestInteropPersonLite();

+        result = DefaultInstance ?? new TestInteropPersonLite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override TestInteropPersonLite DefaultInstanceForType {

@@ -1334,15 +1463,14 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestInteropPersonLite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.codes_.MakeReadOnly();

         result.phone_.MakeReadOnly();

         result.addresses_.MakeReadOnly();

-        TestInteropPersonLite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -1356,6 +1484,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestInteropPersonLite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasName) {

           Name = other.Name;

         }

@@ -1383,6 +1512,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -1447,11 +1577,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetName(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasName = true;

         result.name_ = value;

         return this;

       }

       public Builder ClearName() {

+        PrepareBuilder();

         result.hasName = false;

         result.name_ = "";

         return this;

@@ -1465,11 +1597,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetId(value); }

       }

       public Builder SetId(int value) {

+        PrepareBuilder();

         result.hasId = true;

         result.id_ = value;

         return this;

       }

       public Builder ClearId() {

+        PrepareBuilder();

         result.hasId = false;

         result.id_ = 0;

         return this;

@@ -1484,18 +1618,20 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetEmail(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasEmail = true;

         result.email_ = value;

         return this;

       }

       public Builder ClearEmail() {

+        PrepareBuilder();

         result.hasEmail = false;

         result.email_ = "";

         return this;

       }

       

       public pbc::IPopsicleList<int> CodesList {

-        get { return result.codes_; }

+        get { return PrepareBuilder().codes_; }

       }

       public int CodesCount {

         get { return result.CodesCount; }

@@ -1504,24 +1640,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetCodes(index);

       }

       public Builder SetCodes(int index, int value) {

+        PrepareBuilder();

         result.codes_[index] = value;

         return this;

       }

       public Builder AddCodes(int value) {

+        PrepareBuilder();

         result.codes_.Add(value);

         return this;

       }

       public Builder AddRangeCodes(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.codes_.Add(values);

         return this;

       }

       public Builder ClearCodes() {

+        PrepareBuilder();

         result.codes_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.PhoneNumber> PhoneList {

-        get { return result.phone_; }

+        get { return PrepareBuilder().phone_; }

       }

       public int PhoneCount {

         get { return result.PhoneCount; }

@@ -1531,35 +1671,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetPhone(int index, global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.PhoneNumber value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.phone_[index] = value;

         return this;

       }

       public Builder SetPhone(int index, global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.PhoneNumber.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.phone_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddPhone(global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.PhoneNumber value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.phone_.Add(value);

         return this;

       }

       public Builder AddPhone(global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.PhoneNumber.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.phone_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangePhone(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.PhoneNumber> values) {

+        PrepareBuilder();

         result.phone_.Add(values);

         return this;

       }

       public Builder ClearPhone() {

+        PrepareBuilder();

         result.phone_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.Addresses> AddressesList {

-        get { return result.addresses_; }

+        get { return PrepareBuilder().addresses_; }

       }

       public int AddressesCount {

         get { return result.AddressesCount; }

@@ -1569,29 +1715,35 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetAddresses(int index, global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.Addresses value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.addresses_[index] = value;

         return this;

       }

       public Builder SetAddresses(int index, global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.Addresses.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.addresses_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddAddresses(global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.Addresses value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.addresses_.Add(value);

         return this;

       }

       public Builder AddAddresses(global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.Addresses.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.addresses_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeAddresses(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestInteropPersonLite.Types.Addresses> values) {

+        PrepareBuilder();

         result.addresses_.Add(values);

         return this;

       }

       public Builder ClearAddresses() {

+        PrepareBuilder();

         result.addresses_.Clear();

         return this;

       }

@@ -1715,7 +1867,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestInteropEmployeeIdLite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.SerializableAttribute()]

@@ -1726,21 +1878,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestInteropEmployeeIdLite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestInteropEmployeeIdLite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestInteropEmployeeIdLite result = new TestInteropEmployeeIdLite();

+      bool builderIsReadOnly;

+      TestInteropEmployeeIdLite result;

+      

+      private TestInteropEmployeeIdLite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestInteropEmployeeIdLite original = result;

+          result = new TestInteropEmployeeIdLite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestInteropEmployeeIdLite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestInteropEmployeeIdLite();

+        result = DefaultInstance ?? new TestInteropEmployeeIdLite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override TestInteropEmployeeIdLite DefaultInstanceForType {

@@ -1748,12 +1927,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestInteropEmployeeIdLite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestInteropEmployeeIdLite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -1767,6 +1945,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestInteropEmployeeIdLite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestInteropEmployeeIdLite.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasNumber) {

           Number = other.Number;

         }

@@ -1778,6 +1957,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -1821,11 +2001,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetNumber(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasNumber = true;

         result.number_ = value;

         return this;

       }

       public Builder ClearNumber() {

+        PrepareBuilder();

         result.hasNumber = false;

         result.number_ = "";

         return this;

diff --git a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportLiteProtoFile.cs b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportLiteProtoFile.cs
index 594c9417..98672cf2 100644
--- a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportLiteProtoFile.cs
+++ b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportLiteProtoFile.cs
@@ -151,7 +151,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(ImportMessageLite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -161,21 +161,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new ImportMessageLite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(ImportMessageLite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      ImportMessageLite result;

       

-      ImportMessageLite result = new ImportMessageLite();

+      private ImportMessageLite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          ImportMessageLite original = result;

+          result = new ImportMessageLite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override ImportMessageLite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new ImportMessageLite();

+        result = DefaultInstance ?? new ImportMessageLite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override ImportMessageLite DefaultInstanceForType {

@@ -183,12 +210,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override ImportMessageLite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        ImportMessageLite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -202,6 +228,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(ImportMessageLite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.ImportMessageLite.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasD) {

           D = other.D;

         }

@@ -213,6 +240,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -255,11 +283,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetD(value); }

       }

       public Builder SetD(int value) {

+        PrepareBuilder();

         result.hasD = true;

         result.d_ = value;

         return this;

       }

       public Builder ClearD() {

+        PrepareBuilder();

         result.hasD = false;

         result.d_ = 0;

         return this;

diff --git a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportProtoFile.cs b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportProtoFile.cs
index c5da5537..086dda1d 100644
--- a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportProtoFile.cs
+++ b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportProtoFile.cs
@@ -170,7 +170,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(ImportMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -180,21 +180,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new ImportMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(ImportMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      ImportMessage result;

       

-      ImportMessage result = new ImportMessage();

+      private ImportMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          ImportMessage original = result;

+          result = new ImportMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override ImportMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new ImportMessage();

+        result = DefaultInstance ?? new ImportMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -206,12 +233,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override ImportMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        ImportMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -225,6 +251,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(ImportMessage other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.ImportMessage.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasD) {

           D = other.D;

         }

@@ -237,6 +264,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -292,11 +320,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetD(value); }

       }

       public Builder SetD(int value) {

+        PrepareBuilder();

         result.hasD = true;

         result.d_ = value;

         return this;

       }

       public Builder ClearD() {

+        PrepareBuilder();

         result.hasD = false;

         result.d_ = 0;

         return this;

diff --git a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteImportNonLiteProtoFile.cs b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteImportNonLiteProtoFile.cs
index 7d72f288..2b059eb2 100644
--- a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteImportNonLiteProtoFile.cs
+++ b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteImportNonLiteProtoFile.cs
@@ -140,7 +140,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestLiteImportsNonlite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -150,21 +150,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestLiteImportsNonlite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestLiteImportsNonlite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestLiteImportsNonlite result;

       

-      TestLiteImportsNonlite result = new TestLiteImportsNonlite();

+      private TestLiteImportsNonlite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestLiteImportsNonlite original = result;

+          result = new TestLiteImportsNonlite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestLiteImportsNonlite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestLiteImportsNonlite();

+        result = DefaultInstance ?? new TestLiteImportsNonlite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override TestLiteImportsNonlite DefaultInstanceForType {

@@ -172,12 +199,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestLiteImportsNonlite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestLiteImportsNonlite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -191,6 +217,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestLiteImportsNonlite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestLiteImportsNonlite.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasMessage) {

           MergeMessage(other.Message);

         }

@@ -202,6 +229,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -250,18 +278,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasMessage = true;

         result.message_ = value;

         return this;

       }

       public Builder SetMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasMessage = true;

         result.message_ = builderForValue.Build();

         return this;

       }

       public Builder MergeMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasMessage &&

             result.message_ != global::Google.ProtocolBuffers.TestProtos.TestAllTypes.DefaultInstance) {

             result.message_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.CreateBuilder(result.message_).MergeFrom(value).BuildPartial();

@@ -272,6 +303,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearMessage() {

+        PrepareBuilder();

         result.hasMessage = false;

         result.message_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.DefaultInstance;

         return this;

diff --git a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteProtoFile.cs b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteProtoFile.cs
index 3135a4ba..90c792b3 100644
--- a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteProtoFile.cs
+++ b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteProtoFile.cs
@@ -1369,7 +1369,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(NestedMessage prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1379,21 +1379,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new NestedMessage();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(NestedMessage cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          NestedMessage result;

+          

+          private NestedMessage PrepareBuilder() {

+            if (builderIsReadOnly) {

+              NestedMessage original = result;

+              result = new NestedMessage();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

           

-          NestedMessage result = new NestedMessage();

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override NestedMessage MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new NestedMessage();

+            result = DefaultInstance ?? new NestedMessage();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override NestedMessage DefaultInstanceForType {

@@ -1401,12 +1428,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override NestedMessage BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            NestedMessage returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessageLite other) {

@@ -1420,6 +1446,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(NestedMessage other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasBb) {

               Bb = other.Bb;

             }

@@ -1431,6 +1458,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             uint tag;

             string field_name;

             while (input.ReadTag(out tag, out field_name)) {

@@ -1473,11 +1501,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetBb(value); }

           }

           public Builder SetBb(int value) {

+            PrepareBuilder();

             result.hasBb = true;

             result.bb_ = value;

             return this;

           }

           public Builder ClearBb() {

+            PrepareBuilder();

             result.hasBb = false;

             result.bb_ = 0;

             return this;

@@ -1600,7 +1630,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(OptionalGroup prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1610,21 +1640,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new OptionalGroup();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(OptionalGroup cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          OptionalGroup result;

+          

+          private OptionalGroup PrepareBuilder() {

+            if (builderIsReadOnly) {

+              OptionalGroup original = result;

+              result = new OptionalGroup();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

           

-          OptionalGroup result = new OptionalGroup();

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override OptionalGroup MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new OptionalGroup();

+            result = DefaultInstance ?? new OptionalGroup();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override OptionalGroup DefaultInstanceForType {

@@ -1632,12 +1689,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override OptionalGroup BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            OptionalGroup returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessageLite other) {

@@ -1651,6 +1707,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(OptionalGroup other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.OptionalGroup.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasA) {

               A = other.A;

             }

@@ -1662,6 +1719,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             uint tag;

             string field_name;

             while (input.ReadTag(out tag, out field_name)) {

@@ -1704,11 +1762,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetA(value); }

           }

           public Builder SetA(int value) {

+            PrepareBuilder();

             result.hasA = true;

             result.a_ = value;

             return this;

           }

           public Builder ClearA() {

+            PrepareBuilder();

             result.hasA = false;

             result.a_ = 0;

             return this;

@@ -1831,7 +1891,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(RepeatedGroup prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1841,21 +1901,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new RepeatedGroup();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(RepeatedGroup cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          RepeatedGroup result;

+          

+          private RepeatedGroup PrepareBuilder() {

+            if (builderIsReadOnly) {

+              RepeatedGroup original = result;

+              result = new RepeatedGroup();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

           

-          RepeatedGroup result = new RepeatedGroup();

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override RepeatedGroup MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new RepeatedGroup();

+            result = DefaultInstance ?? new RepeatedGroup();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override RepeatedGroup DefaultInstanceForType {

@@ -1863,12 +1950,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override RepeatedGroup BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            RepeatedGroup returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessageLite other) {

@@ -1882,6 +1968,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(RepeatedGroup other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.RepeatedGroup.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasA) {

               A = other.A;

             }

@@ -1893,6 +1980,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             uint tag;

             string field_name;

             while (input.ReadTag(out tag, out field_name)) {

@@ -1935,11 +2023,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetA(value); }

           }

           public Builder SetA(int value) {

+            PrepareBuilder();

             result.hasA = true;

             result.a_ = value;

             return this;

           }

           public Builder ClearA() {

+            PrepareBuilder();

             result.hasA = false;

             result.a_ = 0;

             return this;

@@ -3546,7 +3636,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestAllTypesLite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -3556,21 +3646,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestAllTypesLite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestAllTypesLite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestAllTypesLite result = new TestAllTypesLite();

+      bool builderIsReadOnly;

+      TestAllTypesLite result;

+      

+      private TestAllTypesLite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestAllTypesLite original = result;

+          result = new TestAllTypesLite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestAllTypesLite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestAllTypesLite();

+        result = DefaultInstance ?? new TestAllTypesLite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override TestAllTypesLite DefaultInstanceForType {

@@ -3578,8 +3695,8 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestAllTypesLite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.repeatedInt32_.MakeReadOnly();

         result.repeatedInt64_.MakeReadOnly();

@@ -3605,9 +3722,8 @@ namespace Google.ProtocolBuffers.TestProtos {
         result.repeatedImportEnum_.MakeReadOnly();

         result.repeatedStringPiece_.MakeReadOnly();

         result.repeatedCord_.MakeReadOnly();

-        TestAllTypesLite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -3621,6 +3737,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestAllTypesLite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasOptionalInt32) {

           OptionalInt32 = other.OptionalInt32;

         }

@@ -3833,6 +3950,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -4206,11 +4324,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalInt32(value); }

       }

       public Builder SetOptionalInt32(int value) {

+        PrepareBuilder();

         result.hasOptionalInt32 = true;

         result.optionalInt32_ = value;

         return this;

       }

       public Builder ClearOptionalInt32() {

+        PrepareBuilder();

         result.hasOptionalInt32 = false;

         result.optionalInt32_ = 0;

         return this;

@@ -4224,11 +4344,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalInt64(value); }

       }

       public Builder SetOptionalInt64(long value) {

+        PrepareBuilder();

         result.hasOptionalInt64 = true;

         result.optionalInt64_ = value;

         return this;

       }

       public Builder ClearOptionalInt64() {

+        PrepareBuilder();

         result.hasOptionalInt64 = false;

         result.optionalInt64_ = 0L;

         return this;

@@ -4244,11 +4366,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetOptionalUint32(uint value) {

+        PrepareBuilder();

         result.hasOptionalUint32 = true;

         result.optionalUint32_ = value;

         return this;

       }

       public Builder ClearOptionalUint32() {

+        PrepareBuilder();

         result.hasOptionalUint32 = false;

         result.optionalUint32_ = 0;

         return this;

@@ -4264,11 +4388,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetOptionalUint64(ulong value) {

+        PrepareBuilder();

         result.hasOptionalUint64 = true;

         result.optionalUint64_ = value;

         return this;

       }

       public Builder ClearOptionalUint64() {

+        PrepareBuilder();

         result.hasOptionalUint64 = false;

         result.optionalUint64_ = 0UL;

         return this;

@@ -4282,11 +4408,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalSint32(value); }

       }

       public Builder SetOptionalSint32(int value) {

+        PrepareBuilder();

         result.hasOptionalSint32 = true;

         result.optionalSint32_ = value;

         return this;

       }

       public Builder ClearOptionalSint32() {

+        PrepareBuilder();

         result.hasOptionalSint32 = false;

         result.optionalSint32_ = 0;

         return this;

@@ -4300,11 +4428,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalSint64(value); }

       }

       public Builder SetOptionalSint64(long value) {

+        PrepareBuilder();

         result.hasOptionalSint64 = true;

         result.optionalSint64_ = value;

         return this;

       }

       public Builder ClearOptionalSint64() {

+        PrepareBuilder();

         result.hasOptionalSint64 = false;

         result.optionalSint64_ = 0;

         return this;

@@ -4320,11 +4450,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetOptionalFixed32(uint value) {

+        PrepareBuilder();

         result.hasOptionalFixed32 = true;

         result.optionalFixed32_ = value;

         return this;

       }

       public Builder ClearOptionalFixed32() {

+        PrepareBuilder();

         result.hasOptionalFixed32 = false;

         result.optionalFixed32_ = 0;

         return this;

@@ -4340,11 +4472,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetOptionalFixed64(ulong value) {

+        PrepareBuilder();

         result.hasOptionalFixed64 = true;

         result.optionalFixed64_ = value;

         return this;

       }

       public Builder ClearOptionalFixed64() {

+        PrepareBuilder();

         result.hasOptionalFixed64 = false;

         result.optionalFixed64_ = 0;

         return this;

@@ -4358,11 +4492,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalSfixed32(value); }

       }

       public Builder SetOptionalSfixed32(int value) {

+        PrepareBuilder();

         result.hasOptionalSfixed32 = true;

         result.optionalSfixed32_ = value;

         return this;

       }

       public Builder ClearOptionalSfixed32() {

+        PrepareBuilder();

         result.hasOptionalSfixed32 = false;

         result.optionalSfixed32_ = 0;

         return this;

@@ -4376,11 +4512,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalSfixed64(value); }

       }

       public Builder SetOptionalSfixed64(long value) {

+        PrepareBuilder();

         result.hasOptionalSfixed64 = true;

         result.optionalSfixed64_ = value;

         return this;

       }

       public Builder ClearOptionalSfixed64() {

+        PrepareBuilder();

         result.hasOptionalSfixed64 = false;

         result.optionalSfixed64_ = 0;

         return this;

@@ -4394,11 +4532,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalFloat(value); }

       }

       public Builder SetOptionalFloat(float value) {

+        PrepareBuilder();

         result.hasOptionalFloat = true;

         result.optionalFloat_ = value;

         return this;

       }

       public Builder ClearOptionalFloat() {

+        PrepareBuilder();

         result.hasOptionalFloat = false;

         result.optionalFloat_ = 0F;

         return this;

@@ -4412,11 +4552,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalDouble(value); }

       }

       public Builder SetOptionalDouble(double value) {

+        PrepareBuilder();

         result.hasOptionalDouble = true;

         result.optionalDouble_ = value;

         return this;

       }

       public Builder ClearOptionalDouble() {

+        PrepareBuilder();

         result.hasOptionalDouble = false;

         result.optionalDouble_ = 0D;

         return this;

@@ -4430,11 +4572,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalBool(value); }

       }

       public Builder SetOptionalBool(bool value) {

+        PrepareBuilder();

         result.hasOptionalBool = true;

         result.optionalBool_ = value;

         return this;

       }

       public Builder ClearOptionalBool() {

+        PrepareBuilder();

         result.hasOptionalBool = false;

         result.optionalBool_ = false;

         return this;

@@ -4449,11 +4593,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalString(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalString = true;

         result.optionalString_ = value;

         return this;

       }

       public Builder ClearOptionalString() {

+        PrepareBuilder();

         result.hasOptionalString = false;

         result.optionalString_ = "";

         return this;

@@ -4468,11 +4614,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalBytes(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalBytes = true;

         result.optionalBytes_ = value;

         return this;

       }

       public Builder ClearOptionalBytes() {

+        PrepareBuilder();

         result.hasOptionalBytes = false;

         result.optionalBytes_ = pb::ByteString.Empty;

         return this;

@@ -4487,18 +4635,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.OptionalGroup value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalGroup = true;

         result.optionalGroup_ = value;

         return this;

       }

       public Builder SetOptionalGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.OptionalGroup.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalGroup = true;

         result.optionalGroup_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.OptionalGroup value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalGroup &&

             result.optionalGroup_ != global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.OptionalGroup.DefaultInstance) {

             result.optionalGroup_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.OptionalGroup.CreateBuilder(result.optionalGroup_).MergeFrom(value).BuildPartial();

@@ -4509,6 +4660,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalGroup() {

+        PrepareBuilder();

         result.hasOptionalGroup = false;

         result.optionalGroup_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.OptionalGroup.DefaultInstance;

         return this;

@@ -4523,18 +4675,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalNestedMessage = true;

         result.optionalNestedMessage_ = value;

         return this;

       }

       public Builder SetOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalNestedMessage = true;

         result.optionalNestedMessage_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalNestedMessage &&

             result.optionalNestedMessage_ != global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage.DefaultInstance) {

             result.optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage.CreateBuilder(result.optionalNestedMessage_).MergeFrom(value).BuildPartial();

@@ -4545,6 +4700,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalNestedMessage() {

+        PrepareBuilder();

         result.hasOptionalNestedMessage = false;

         result.optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage.DefaultInstance;

         return this;

@@ -4559,18 +4715,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalForeignMessage = true;

         result.optionalForeignMessage_ = value;

         return this;

       }

       public Builder SetOptionalForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalForeignMessage = true;

         result.optionalForeignMessage_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalForeignMessage &&

             result.optionalForeignMessage_ != global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite.DefaultInstance) {

             result.optionalForeignMessage_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite.CreateBuilder(result.optionalForeignMessage_).MergeFrom(value).BuildPartial();

@@ -4581,6 +4740,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalForeignMessage() {

+        PrepareBuilder();

         result.hasOptionalForeignMessage = false;

         result.optionalForeignMessage_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite.DefaultInstance;

         return this;

@@ -4595,18 +4755,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessageLite value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalImportMessage = true;

         result.optionalImportMessage_ = value;

         return this;

       }

       public Builder SetOptionalImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessageLite.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalImportMessage = true;

         result.optionalImportMessage_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessageLite value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalImportMessage &&

             result.optionalImportMessage_ != global::Google.ProtocolBuffers.TestProtos.ImportMessageLite.DefaultInstance) {

             result.optionalImportMessage_ = global::Google.ProtocolBuffers.TestProtos.ImportMessageLite.CreateBuilder(result.optionalImportMessage_).MergeFrom(value).BuildPartial();

@@ -4617,6 +4780,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalImportMessage() {

+        PrepareBuilder();

         result.hasOptionalImportMessage = false;

         result.optionalImportMessage_ = global::Google.ProtocolBuffers.TestProtos.ImportMessageLite.DefaultInstance;

         return this;

@@ -4630,11 +4794,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalNestedEnum(value); }

       }

       public Builder SetOptionalNestedEnum(global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedEnum value) {

+        PrepareBuilder();

         result.hasOptionalNestedEnum = true;

         result.optionalNestedEnum_ = value;

         return this;

       }

       public Builder ClearOptionalNestedEnum() {

+        PrepareBuilder();

         result.hasOptionalNestedEnum = false;

         result.optionalNestedEnum_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedEnum.FOO;

         return this;

@@ -4648,11 +4814,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalForeignEnum(value); }

       }

       public Builder SetOptionalForeignEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite value) {

+        PrepareBuilder();

         result.hasOptionalForeignEnum = true;

         result.optionalForeignEnum_ = value;

         return this;

       }

       public Builder ClearOptionalForeignEnum() {

+        PrepareBuilder();

         result.hasOptionalForeignEnum = false;

         result.optionalForeignEnum_ = global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite.FOREIGN_LITE_FOO;

         return this;

@@ -4666,11 +4834,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalImportEnum(value); }

       }

       public Builder SetOptionalImportEnum(global::Google.ProtocolBuffers.TestProtos.ImportEnumLite value) {

+        PrepareBuilder();

         result.hasOptionalImportEnum = true;

         result.optionalImportEnum_ = value;

         return this;

       }

       public Builder ClearOptionalImportEnum() {

+        PrepareBuilder();

         result.hasOptionalImportEnum = false;

         result.optionalImportEnum_ = global::Google.ProtocolBuffers.TestProtos.ImportEnumLite.IMPORT_LITE_FOO;

         return this;

@@ -4685,11 +4855,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalStringPiece(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalStringPiece = true;

         result.optionalStringPiece_ = value;

         return this;

       }

       public Builder ClearOptionalStringPiece() {

+        PrepareBuilder();

         result.hasOptionalStringPiece = false;

         result.optionalStringPiece_ = "";

         return this;

@@ -4704,18 +4876,20 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalCord(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalCord = true;

         result.optionalCord_ = value;

         return this;

       }

       public Builder ClearOptionalCord() {

+        PrepareBuilder();

         result.hasOptionalCord = false;

         result.optionalCord_ = "";

         return this;

       }

       

       public pbc::IPopsicleList<int> RepeatedInt32List {

-        get { return result.repeatedInt32_; }

+        get { return PrepareBuilder().repeatedInt32_; }

       }

       public int RepeatedInt32Count {

         get { return result.RepeatedInt32Count; }

@@ -4724,24 +4898,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedInt32(index);

       }

       public Builder SetRepeatedInt32(int index, int value) {

+        PrepareBuilder();

         result.repeatedInt32_[index] = value;

         return this;

       }

       public Builder AddRepeatedInt32(int value) {

+        PrepareBuilder();

         result.repeatedInt32_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedInt32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.repeatedInt32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedInt32() {

+        PrepareBuilder();

         result.repeatedInt32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> RepeatedInt64List {

-        get { return result.repeatedInt64_; }

+        get { return PrepareBuilder().repeatedInt64_; }

       }

       public int RepeatedInt64Count {

         get { return result.RepeatedInt64Count; }

@@ -4750,25 +4928,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedInt64(index);

       }

       public Builder SetRepeatedInt64(int index, long value) {

+        PrepareBuilder();

         result.repeatedInt64_[index] = value;

         return this;

       }

       public Builder AddRepeatedInt64(long value) {

+        PrepareBuilder();

         result.repeatedInt64_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedInt64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.repeatedInt64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedInt64() {

+        PrepareBuilder();

         result.repeatedInt64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> RepeatedUint32List {

-        get { return result.repeatedUint32_; }

+        get { return PrepareBuilder().repeatedUint32_; }

       }

       public int RepeatedUint32Count {

         get { return result.RepeatedUint32Count; }

@@ -4779,27 +4961,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedUint32(int index, uint value) {

+        PrepareBuilder();

         result.repeatedUint32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedUint32(uint value) {

+        PrepareBuilder();

         result.repeatedUint32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedUint32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.repeatedUint32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedUint32() {

+        PrepareBuilder();

         result.repeatedUint32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> RepeatedUint64List {

-        get { return result.repeatedUint64_; }

+        get { return PrepareBuilder().repeatedUint64_; }

       }

       public int RepeatedUint64Count {

         get { return result.RepeatedUint64Count; }

@@ -4810,26 +4996,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedUint64(int index, ulong value) {

+        PrepareBuilder();

         result.repeatedUint64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedUint64(ulong value) {

+        PrepareBuilder();

         result.repeatedUint64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedUint64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.repeatedUint64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedUint64() {

+        PrepareBuilder();

         result.repeatedUint64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> RepeatedSint32List {

-        get { return result.repeatedSint32_; }

+        get { return PrepareBuilder().repeatedSint32_; }

       }

       public int RepeatedSint32Count {

         get { return result.RepeatedSint32Count; }

@@ -4838,24 +5028,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedSint32(index);

       }

       public Builder SetRepeatedSint32(int index, int value) {

+        PrepareBuilder();

         result.repeatedSint32_[index] = value;

         return this;

       }

       public Builder AddRepeatedSint32(int value) {

+        PrepareBuilder();

         result.repeatedSint32_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedSint32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.repeatedSint32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedSint32() {

+        PrepareBuilder();

         result.repeatedSint32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> RepeatedSint64List {

-        get { return result.repeatedSint64_; }

+        get { return PrepareBuilder().repeatedSint64_; }

       }

       public int RepeatedSint64Count {

         get { return result.RepeatedSint64Count; }

@@ -4864,25 +5058,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedSint64(index);

       }

       public Builder SetRepeatedSint64(int index, long value) {

+        PrepareBuilder();

         result.repeatedSint64_[index] = value;

         return this;

       }

       public Builder AddRepeatedSint64(long value) {

+        PrepareBuilder();

         result.repeatedSint64_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedSint64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.repeatedSint64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedSint64() {

+        PrepareBuilder();

         result.repeatedSint64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> RepeatedFixed32List {

-        get { return result.repeatedFixed32_; }

+        get { return PrepareBuilder().repeatedFixed32_; }

       }

       public int RepeatedFixed32Count {

         get { return result.RepeatedFixed32Count; }

@@ -4893,27 +5091,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedFixed32(int index, uint value) {

+        PrepareBuilder();

         result.repeatedFixed32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedFixed32(uint value) {

+        PrepareBuilder();

         result.repeatedFixed32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedFixed32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.repeatedFixed32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFixed32() {

+        PrepareBuilder();

         result.repeatedFixed32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> RepeatedFixed64List {

-        get { return result.repeatedFixed64_; }

+        get { return PrepareBuilder().repeatedFixed64_; }

       }

       public int RepeatedFixed64Count {

         get { return result.RepeatedFixed64Count; }

@@ -4924,26 +5126,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedFixed64(int index, ulong value) {

+        PrepareBuilder();

         result.repeatedFixed64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedFixed64(ulong value) {

+        PrepareBuilder();

         result.repeatedFixed64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedFixed64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.repeatedFixed64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFixed64() {

+        PrepareBuilder();

         result.repeatedFixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> RepeatedSfixed32List {

-        get { return result.repeatedSfixed32_; }

+        get { return PrepareBuilder().repeatedSfixed32_; }

       }

       public int RepeatedSfixed32Count {

         get { return result.RepeatedSfixed32Count; }

@@ -4952,24 +5158,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedSfixed32(index);

       }

       public Builder SetRepeatedSfixed32(int index, int value) {

+        PrepareBuilder();

         result.repeatedSfixed32_[index] = value;

         return this;

       }

       public Builder AddRepeatedSfixed32(int value) {

+        PrepareBuilder();

         result.repeatedSfixed32_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedSfixed32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.repeatedSfixed32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedSfixed32() {

+        PrepareBuilder();

         result.repeatedSfixed32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> RepeatedSfixed64List {

-        get { return result.repeatedSfixed64_; }

+        get { return PrepareBuilder().repeatedSfixed64_; }

       }

       public int RepeatedSfixed64Count {

         get { return result.RepeatedSfixed64Count; }

@@ -4978,24 +5188,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedSfixed64(index);

       }

       public Builder SetRepeatedSfixed64(int index, long value) {

+        PrepareBuilder();

         result.repeatedSfixed64_[index] = value;

         return this;

       }

       public Builder AddRepeatedSfixed64(long value) {

+        PrepareBuilder();

         result.repeatedSfixed64_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedSfixed64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.repeatedSfixed64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedSfixed64() {

+        PrepareBuilder();

         result.repeatedSfixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<float> RepeatedFloatList {

-        get { return result.repeatedFloat_; }

+        get { return PrepareBuilder().repeatedFloat_; }

       }

       public int RepeatedFloatCount {

         get { return result.RepeatedFloatCount; }

@@ -5004,24 +5218,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedFloat(index);

       }

       public Builder SetRepeatedFloat(int index, float value) {

+        PrepareBuilder();

         result.repeatedFloat_[index] = value;

         return this;

       }

       public Builder AddRepeatedFloat(float value) {

+        PrepareBuilder();

         result.repeatedFloat_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedFloat(scg::IEnumerable<float> values) {

+        PrepareBuilder();

         result.repeatedFloat_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFloat() {

+        PrepareBuilder();

         result.repeatedFloat_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<double> RepeatedDoubleList {

-        get { return result.repeatedDouble_; }

+        get { return PrepareBuilder().repeatedDouble_; }

       }

       public int RepeatedDoubleCount {

         get { return result.RepeatedDoubleCount; }

@@ -5030,24 +5248,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedDouble(index);

       }

       public Builder SetRepeatedDouble(int index, double value) {

+        PrepareBuilder();

         result.repeatedDouble_[index] = value;

         return this;

       }

       public Builder AddRepeatedDouble(double value) {

+        PrepareBuilder();

         result.repeatedDouble_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedDouble(scg::IEnumerable<double> values) {

+        PrepareBuilder();

         result.repeatedDouble_.Add(values);

         return this;

       }

       public Builder ClearRepeatedDouble() {

+        PrepareBuilder();

         result.repeatedDouble_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<bool> RepeatedBoolList {

-        get { return result.repeatedBool_; }

+        get { return PrepareBuilder().repeatedBool_; }

       }

       public int RepeatedBoolCount {

         get { return result.RepeatedBoolCount; }

@@ -5056,24 +5278,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedBool(index);

       }

       public Builder SetRepeatedBool(int index, bool value) {

+        PrepareBuilder();

         result.repeatedBool_[index] = value;

         return this;

       }

       public Builder AddRepeatedBool(bool value) {

+        PrepareBuilder();

         result.repeatedBool_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedBool(scg::IEnumerable<bool> values) {

+        PrepareBuilder();

         result.repeatedBool_.Add(values);

         return this;

       }

       public Builder ClearRepeatedBool() {

+        PrepareBuilder();

         result.repeatedBool_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedStringList {

-        get { return result.repeatedString_; }

+        get { return PrepareBuilder().repeatedString_; }

       }

       public int RepeatedStringCount {

         get { return result.RepeatedStringCount; }

@@ -5083,25 +5309,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedString(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedString_[index] = value;

         return this;

       }

       public Builder AddRepeatedString(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedString_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedString(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedString_.Add(values);

         return this;

       }

       public Builder ClearRepeatedString() {

+        PrepareBuilder();

         result.repeatedString_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<pb::ByteString> RepeatedBytesList {

-        get { return result.repeatedBytes_; }

+        get { return PrepareBuilder().repeatedBytes_; }

       }

       public int RepeatedBytesCount {

         get { return result.RepeatedBytesCount; }

@@ -5111,25 +5341,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedBytes(int index, pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedBytes_[index] = value;

         return this;

       }

       public Builder AddRepeatedBytes(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedBytes_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedBytes(scg::IEnumerable<pb::ByteString> values) {

+        PrepareBuilder();

         result.repeatedBytes_.Add(values);

         return this;

       }

       public Builder ClearRepeatedBytes() {

+        PrepareBuilder();

         result.repeatedBytes_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.RepeatedGroup> RepeatedGroupList {

-        get { return result.repeatedGroup_; }

+        get { return PrepareBuilder().repeatedGroup_; }

       }

       public int RepeatedGroupCount {

         get { return result.RepeatedGroupCount; }

@@ -5139,35 +5373,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedGroup(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.RepeatedGroup value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedGroup_[index] = value;

         return this;

       }

       public Builder SetRepeatedGroup(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.RepeatedGroup.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedGroup_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.RepeatedGroup value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedGroup_.Add(value);

         return this;

       }

       public Builder AddRepeatedGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.RepeatedGroup.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedGroup_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedGroup(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.RepeatedGroup> values) {

+        PrepareBuilder();

         result.repeatedGroup_.Add(values);

         return this;

       }

       public Builder ClearRepeatedGroup() {

+        PrepareBuilder();

         result.repeatedGroup_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage> RepeatedNestedMessageList {

-        get { return result.repeatedNestedMessage_; }

+        get { return PrepareBuilder().repeatedNestedMessage_; }

       }

       public int RepeatedNestedMessageCount {

         get { return result.RepeatedNestedMessageCount; }

@@ -5177,35 +5417,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedNestedMessage(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedNestedMessage_[index] = value;

         return this;

       }

       public Builder SetRepeatedNestedMessage(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedNestedMessage_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedNestedMessage_.Add(value);

         return this;

       }

       public Builder AddRepeatedNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedNestedMessage_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedNestedMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage> values) {

+        PrepareBuilder();

         result.repeatedNestedMessage_.Add(values);

         return this;

       }

       public Builder ClearRepeatedNestedMessage() {

+        PrepareBuilder();

         result.repeatedNestedMessage_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite> RepeatedForeignMessageList {

-        get { return result.repeatedForeignMessage_; }

+        get { return PrepareBuilder().repeatedForeignMessage_; }

       }

       public int RepeatedForeignMessageCount {

         get { return result.RepeatedForeignMessageCount; }

@@ -5215,35 +5461,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedForeignMessage(int index, global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedForeignMessage_[index] = value;

         return this;

       }

       public Builder SetRepeatedForeignMessage(int index, global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedForeignMessage_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedForeignMessage_.Add(value);

         return this;

       }

       public Builder AddRepeatedForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedForeignMessage_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedForeignMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite> values) {

+        PrepareBuilder();

         result.repeatedForeignMessage_.Add(values);

         return this;

       }

       public Builder ClearRepeatedForeignMessage() {

+        PrepareBuilder();

         result.repeatedForeignMessage_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ImportMessageLite> RepeatedImportMessageList {

-        get { return result.repeatedImportMessage_; }

+        get { return PrepareBuilder().repeatedImportMessage_; }

       }

       public int RepeatedImportMessageCount {

         get { return result.RepeatedImportMessageCount; }

@@ -5253,35 +5505,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedImportMessage(int index, global::Google.ProtocolBuffers.TestProtos.ImportMessageLite value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedImportMessage_[index] = value;

         return this;

       }

       public Builder SetRepeatedImportMessage(int index, global::Google.ProtocolBuffers.TestProtos.ImportMessageLite.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedImportMessage_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessageLite value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedImportMessage_.Add(value);

         return this;

       }

       public Builder AddRepeatedImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessageLite.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedImportMessage_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedImportMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ImportMessageLite> values) {

+        PrepareBuilder();

         result.repeatedImportMessage_.Add(values);

         return this;

       }

       public Builder ClearRepeatedImportMessage() {

+        PrepareBuilder();

         result.repeatedImportMessage_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedEnum> RepeatedNestedEnumList {

-        get { return result.repeatedNestedEnum_; }

+        get { return PrepareBuilder().repeatedNestedEnum_; }

       }

       public int RepeatedNestedEnumCount {

         get { return result.RepeatedNestedEnumCount; }

@@ -5290,24 +5548,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedNestedEnum(index);

       }

       public Builder SetRepeatedNestedEnum(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedEnum value) {

+        PrepareBuilder();

         result.repeatedNestedEnum_[index] = value;

         return this;

       }

       public Builder AddRepeatedNestedEnum(global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedEnum value) {

+        PrepareBuilder();

         result.repeatedNestedEnum_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedNestedEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedEnum> values) {

+        PrepareBuilder();

         result.repeatedNestedEnum_.Add(values);

         return this;

       }

       public Builder ClearRepeatedNestedEnum() {

+        PrepareBuilder();

         result.repeatedNestedEnum_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite> RepeatedForeignEnumList {

-        get { return result.repeatedForeignEnum_; }

+        get { return PrepareBuilder().repeatedForeignEnum_; }

       }

       public int RepeatedForeignEnumCount {

         get { return result.RepeatedForeignEnumCount; }

@@ -5316,24 +5578,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedForeignEnum(index);

       }

       public Builder SetRepeatedForeignEnum(int index, global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite value) {

+        PrepareBuilder();

         result.repeatedForeignEnum_[index] = value;

         return this;

       }

       public Builder AddRepeatedForeignEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite value) {

+        PrepareBuilder();

         result.repeatedForeignEnum_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedForeignEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite> values) {

+        PrepareBuilder();

         result.repeatedForeignEnum_.Add(values);

         return this;

       }

       public Builder ClearRepeatedForeignEnum() {

+        PrepareBuilder();

         result.repeatedForeignEnum_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ImportEnumLite> RepeatedImportEnumList {

-        get { return result.repeatedImportEnum_; }

+        get { return PrepareBuilder().repeatedImportEnum_; }

       }

       public int RepeatedImportEnumCount {

         get { return result.RepeatedImportEnumCount; }

@@ -5342,24 +5608,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedImportEnum(index);

       }

       public Builder SetRepeatedImportEnum(int index, global::Google.ProtocolBuffers.TestProtos.ImportEnumLite value) {

+        PrepareBuilder();

         result.repeatedImportEnum_[index] = value;

         return this;

       }

       public Builder AddRepeatedImportEnum(global::Google.ProtocolBuffers.TestProtos.ImportEnumLite value) {

+        PrepareBuilder();

         result.repeatedImportEnum_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedImportEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ImportEnumLite> values) {

+        PrepareBuilder();

         result.repeatedImportEnum_.Add(values);

         return this;

       }

       public Builder ClearRepeatedImportEnum() {

+        PrepareBuilder();

         result.repeatedImportEnum_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedStringPieceList {

-        get { return result.repeatedStringPiece_; }

+        get { return PrepareBuilder().repeatedStringPiece_; }

       }

       public int RepeatedStringPieceCount {

         get { return result.RepeatedStringPieceCount; }

@@ -5369,25 +5639,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedStringPiece(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedStringPiece_[index] = value;

         return this;

       }

       public Builder AddRepeatedStringPiece(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedStringPiece_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedStringPiece(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedStringPiece_.Add(values);

         return this;

       }

       public Builder ClearRepeatedStringPiece() {

+        PrepareBuilder();

         result.repeatedStringPiece_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedCordList {

-        get { return result.repeatedCord_; }

+        get { return PrepareBuilder().repeatedCord_; }

       }

       public int RepeatedCordCount {

         get { return result.RepeatedCordCount; }

@@ -5397,19 +5671,23 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedCord(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedCord_[index] = value;

         return this;

       }

       public Builder AddRepeatedCord(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedCord_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedCord(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedCord_.Add(values);

         return this;

       }

       public Builder ClearRepeatedCord() {

+        PrepareBuilder();

         result.repeatedCord_.Clear();

         return this;

       }

@@ -5422,11 +5700,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultInt32(value); }

       }

       public Builder SetDefaultInt32(int value) {

+        PrepareBuilder();

         result.hasDefaultInt32 = true;

         result.defaultInt32_ = value;

         return this;

       }

       public Builder ClearDefaultInt32() {

+        PrepareBuilder();

         result.hasDefaultInt32 = false;

         result.defaultInt32_ = 41;

         return this;

@@ -5440,11 +5720,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultInt64(value); }

       }

       public Builder SetDefaultInt64(long value) {

+        PrepareBuilder();

         result.hasDefaultInt64 = true;

         result.defaultInt64_ = value;

         return this;

       }

       public Builder ClearDefaultInt64() {

+        PrepareBuilder();

         result.hasDefaultInt64 = false;

         result.defaultInt64_ = 42L;

         return this;

@@ -5460,11 +5742,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetDefaultUint32(uint value) {

+        PrepareBuilder();

         result.hasDefaultUint32 = true;

         result.defaultUint32_ = value;

         return this;

       }

       public Builder ClearDefaultUint32() {

+        PrepareBuilder();

         result.hasDefaultUint32 = false;

         result.defaultUint32_ = 43;

         return this;

@@ -5480,11 +5764,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetDefaultUint64(ulong value) {

+        PrepareBuilder();

         result.hasDefaultUint64 = true;

         result.defaultUint64_ = value;

         return this;

       }

       public Builder ClearDefaultUint64() {

+        PrepareBuilder();

         result.hasDefaultUint64 = false;

         result.defaultUint64_ = 44UL;

         return this;

@@ -5498,11 +5784,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultSint32(value); }

       }

       public Builder SetDefaultSint32(int value) {

+        PrepareBuilder();

         result.hasDefaultSint32 = true;

         result.defaultSint32_ = value;

         return this;

       }

       public Builder ClearDefaultSint32() {

+        PrepareBuilder();

         result.hasDefaultSint32 = false;

         result.defaultSint32_ = -45;

         return this;

@@ -5516,11 +5804,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultSint64(value); }

       }

       public Builder SetDefaultSint64(long value) {

+        PrepareBuilder();

         result.hasDefaultSint64 = true;

         result.defaultSint64_ = value;

         return this;

       }

       public Builder ClearDefaultSint64() {

+        PrepareBuilder();

         result.hasDefaultSint64 = false;

         result.defaultSint64_ = 46;

         return this;

@@ -5536,11 +5826,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetDefaultFixed32(uint value) {

+        PrepareBuilder();

         result.hasDefaultFixed32 = true;

         result.defaultFixed32_ = value;

         return this;

       }

       public Builder ClearDefaultFixed32() {

+        PrepareBuilder();

         result.hasDefaultFixed32 = false;

         result.defaultFixed32_ = 47;

         return this;

@@ -5556,11 +5848,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetDefaultFixed64(ulong value) {

+        PrepareBuilder();

         result.hasDefaultFixed64 = true;

         result.defaultFixed64_ = value;

         return this;

       }

       public Builder ClearDefaultFixed64() {

+        PrepareBuilder();

         result.hasDefaultFixed64 = false;

         result.defaultFixed64_ = 48;

         return this;

@@ -5574,11 +5868,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultSfixed32(value); }

       }

       public Builder SetDefaultSfixed32(int value) {

+        PrepareBuilder();

         result.hasDefaultSfixed32 = true;

         result.defaultSfixed32_ = value;

         return this;

       }

       public Builder ClearDefaultSfixed32() {

+        PrepareBuilder();

         result.hasDefaultSfixed32 = false;

         result.defaultSfixed32_ = 49;

         return this;

@@ -5592,11 +5888,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultSfixed64(value); }

       }

       public Builder SetDefaultSfixed64(long value) {

+        PrepareBuilder();

         result.hasDefaultSfixed64 = true;

         result.defaultSfixed64_ = value;

         return this;

       }

       public Builder ClearDefaultSfixed64() {

+        PrepareBuilder();

         result.hasDefaultSfixed64 = false;

         result.defaultSfixed64_ = -50;

         return this;

@@ -5610,11 +5908,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultFloat(value); }

       }

       public Builder SetDefaultFloat(float value) {

+        PrepareBuilder();

         result.hasDefaultFloat = true;

         result.defaultFloat_ = value;

         return this;

       }

       public Builder ClearDefaultFloat() {

+        PrepareBuilder();

         result.hasDefaultFloat = false;

         result.defaultFloat_ = 51.5F;

         return this;

@@ -5628,11 +5928,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultDouble(value); }

       }

       public Builder SetDefaultDouble(double value) {

+        PrepareBuilder();

         result.hasDefaultDouble = true;

         result.defaultDouble_ = value;

         return this;

       }

       public Builder ClearDefaultDouble() {

+        PrepareBuilder();

         result.hasDefaultDouble = false;

         result.defaultDouble_ = 52000D;

         return this;

@@ -5646,11 +5948,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultBool(value); }

       }

       public Builder SetDefaultBool(bool value) {

+        PrepareBuilder();

         result.hasDefaultBool = true;

         result.defaultBool_ = value;

         return this;

       }

       public Builder ClearDefaultBool() {

+        PrepareBuilder();

         result.hasDefaultBool = false;

         result.defaultBool_ = true;

         return this;

@@ -5665,11 +5969,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetDefaultString(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDefaultString = true;

         result.defaultString_ = value;

         return this;

       }

       public Builder ClearDefaultString() {

+        PrepareBuilder();

         result.hasDefaultString = false;

         result.defaultString_ = "hello";

         return this;

@@ -5684,11 +5990,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetDefaultBytes(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDefaultBytes = true;

         result.defaultBytes_ = value;

         return this;

       }

       public Builder ClearDefaultBytes() {

+        PrepareBuilder();

         result.hasDefaultBytes = false;

         result.defaultBytes_ = pb::ByteString.FromBase64("d29ybGQ=");

         return this;

@@ -5702,11 +6010,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultNestedEnum(value); }

       }

       public Builder SetDefaultNestedEnum(global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedEnum value) {

+        PrepareBuilder();

         result.hasDefaultNestedEnum = true;

         result.defaultNestedEnum_ = value;

         return this;

       }

       public Builder ClearDefaultNestedEnum() {

+        PrepareBuilder();

         result.hasDefaultNestedEnum = false;

         result.defaultNestedEnum_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedEnum.BAR;

         return this;

@@ -5720,11 +6030,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultForeignEnum(value); }

       }

       public Builder SetDefaultForeignEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite value) {

+        PrepareBuilder();

         result.hasDefaultForeignEnum = true;

         result.defaultForeignEnum_ = value;

         return this;

       }

       public Builder ClearDefaultForeignEnum() {

+        PrepareBuilder();

         result.hasDefaultForeignEnum = false;

         result.defaultForeignEnum_ = global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite.FOREIGN_LITE_BAR;

         return this;

@@ -5738,11 +6050,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultImportEnum(value); }

       }

       public Builder SetDefaultImportEnum(global::Google.ProtocolBuffers.TestProtos.ImportEnumLite value) {

+        PrepareBuilder();

         result.hasDefaultImportEnum = true;

         result.defaultImportEnum_ = value;

         return this;

       }

       public Builder ClearDefaultImportEnum() {

+        PrepareBuilder();

         result.hasDefaultImportEnum = false;

         result.defaultImportEnum_ = global::Google.ProtocolBuffers.TestProtos.ImportEnumLite.IMPORT_LITE_BAR;

         return this;

@@ -5757,11 +6071,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetDefaultStringPiece(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDefaultStringPiece = true;

         result.defaultStringPiece_ = value;

         return this;

       }

       public Builder ClearDefaultStringPiece() {

+        PrepareBuilder();

         result.hasDefaultStringPiece = false;

         result.defaultStringPiece_ = "abc";

         return this;

@@ -5776,11 +6092,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetDefaultCord(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDefaultCord = true;

         result.defaultCord_ = value;

         return this;

       }

       public Builder ClearDefaultCord() {

+        PrepareBuilder();

         result.hasDefaultCord = false;

         result.defaultCord_ = "123";

         return this;

@@ -5903,7 +6221,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(ForeignMessageLite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -5913,21 +6231,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new ForeignMessageLite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(ForeignMessageLite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      ForeignMessageLite result;

+      

+      private ForeignMessageLite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          ForeignMessageLite original = result;

+          result = new ForeignMessageLite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      ForeignMessageLite result = new ForeignMessageLite();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override ForeignMessageLite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new ForeignMessageLite();

+        result = DefaultInstance ?? new ForeignMessageLite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override ForeignMessageLite DefaultInstanceForType {

@@ -5935,12 +6280,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override ForeignMessageLite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        ForeignMessageLite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -5954,6 +6298,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(ForeignMessageLite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasC) {

           C = other.C;

         }

@@ -5965,6 +6310,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -6007,11 +6353,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetC(value); }

       }

       public Builder SetC(int value) {

+        PrepareBuilder();

         result.hasC = true;

         result.c_ = value;

         return this;

       }

       public Builder ClearC() {

+        PrepareBuilder();

         result.hasC = false;

         result.c_ = 0;

         return this;

@@ -6572,7 +6920,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestPackedTypesLite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -6582,21 +6930,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestPackedTypesLite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestPackedTypesLite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestPackedTypesLite result;

       

-      TestPackedTypesLite result = new TestPackedTypesLite();

+      private TestPackedTypesLite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestPackedTypesLite original = result;

+          result = new TestPackedTypesLite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestPackedTypesLite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestPackedTypesLite();

+        result = DefaultInstance ?? new TestPackedTypesLite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override TestPackedTypesLite DefaultInstanceForType {

@@ -6604,8 +6979,8 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestPackedTypesLite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.packedInt32_.MakeReadOnly();

         result.packedInt64_.MakeReadOnly();

@@ -6621,9 +6996,8 @@ namespace Google.ProtocolBuffers.TestProtos {
         result.packedDouble_.MakeReadOnly();

         result.packedBool_.MakeReadOnly();

         result.packedEnum_.MakeReadOnly();

-        TestPackedTypesLite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -6637,6 +7011,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestPackedTypesLite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestPackedTypesLite.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.packedInt32_.Count != 0) {

           result.packedInt32_.Add(other.packedInt32_);

         }

@@ -6687,6 +7062,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -6789,7 +7165,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       

       public pbc::IPopsicleList<int> PackedInt32List {

-        get { return result.packedInt32_; }

+        get { return PrepareBuilder().packedInt32_; }

       }

       public int PackedInt32Count {

         get { return result.PackedInt32Count; }

@@ -6798,24 +7174,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedInt32(index);

       }

       public Builder SetPackedInt32(int index, int value) {

+        PrepareBuilder();

         result.packedInt32_[index] = value;

         return this;

       }

       public Builder AddPackedInt32(int value) {

+        PrepareBuilder();

         result.packedInt32_.Add(value);

         return this;

       }

       public Builder AddRangePackedInt32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.packedInt32_.Add(values);

         return this;

       }

       public Builder ClearPackedInt32() {

+        PrepareBuilder();

         result.packedInt32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> PackedInt64List {

-        get { return result.packedInt64_; }

+        get { return PrepareBuilder().packedInt64_; }

       }

       public int PackedInt64Count {

         get { return result.PackedInt64Count; }

@@ -6824,25 +7204,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedInt64(index);

       }

       public Builder SetPackedInt64(int index, long value) {

+        PrepareBuilder();

         result.packedInt64_[index] = value;

         return this;

       }

       public Builder AddPackedInt64(long value) {

+        PrepareBuilder();

         result.packedInt64_.Add(value);

         return this;

       }

       public Builder AddRangePackedInt64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.packedInt64_.Add(values);

         return this;

       }

       public Builder ClearPackedInt64() {

+        PrepareBuilder();

         result.packedInt64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> PackedUint32List {

-        get { return result.packedUint32_; }

+        get { return PrepareBuilder().packedUint32_; }

       }

       public int PackedUint32Count {

         get { return result.PackedUint32Count; }

@@ -6853,27 +7237,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetPackedUint32(int index, uint value) {

+        PrepareBuilder();

         result.packedUint32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddPackedUint32(uint value) {

+        PrepareBuilder();

         result.packedUint32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangePackedUint32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.packedUint32_.Add(values);

         return this;

       }

       public Builder ClearPackedUint32() {

+        PrepareBuilder();

         result.packedUint32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> PackedUint64List {

-        get { return result.packedUint64_; }

+        get { return PrepareBuilder().packedUint64_; }

       }

       public int PackedUint64Count {

         get { return result.PackedUint64Count; }

@@ -6884,26 +7272,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetPackedUint64(int index, ulong value) {

+        PrepareBuilder();

         result.packedUint64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddPackedUint64(ulong value) {

+        PrepareBuilder();

         result.packedUint64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangePackedUint64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.packedUint64_.Add(values);

         return this;

       }

       public Builder ClearPackedUint64() {

+        PrepareBuilder();

         result.packedUint64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> PackedSint32List {

-        get { return result.packedSint32_; }

+        get { return PrepareBuilder().packedSint32_; }

       }

       public int PackedSint32Count {

         get { return result.PackedSint32Count; }

@@ -6912,24 +7304,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedSint32(index);

       }

       public Builder SetPackedSint32(int index, int value) {

+        PrepareBuilder();

         result.packedSint32_[index] = value;

         return this;

       }

       public Builder AddPackedSint32(int value) {

+        PrepareBuilder();

         result.packedSint32_.Add(value);

         return this;

       }

       public Builder AddRangePackedSint32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.packedSint32_.Add(values);

         return this;

       }

       public Builder ClearPackedSint32() {

+        PrepareBuilder();

         result.packedSint32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> PackedSint64List {

-        get { return result.packedSint64_; }

+        get { return PrepareBuilder().packedSint64_; }

       }

       public int PackedSint64Count {

         get { return result.PackedSint64Count; }

@@ -6938,25 +7334,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedSint64(index);

       }

       public Builder SetPackedSint64(int index, long value) {

+        PrepareBuilder();

         result.packedSint64_[index] = value;

         return this;

       }

       public Builder AddPackedSint64(long value) {

+        PrepareBuilder();

         result.packedSint64_.Add(value);

         return this;

       }

       public Builder AddRangePackedSint64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.packedSint64_.Add(values);

         return this;

       }

       public Builder ClearPackedSint64() {

+        PrepareBuilder();

         result.packedSint64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> PackedFixed32List {

-        get { return result.packedFixed32_; }

+        get { return PrepareBuilder().packedFixed32_; }

       }

       public int PackedFixed32Count {

         get { return result.PackedFixed32Count; }

@@ -6967,27 +7367,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetPackedFixed32(int index, uint value) {

+        PrepareBuilder();

         result.packedFixed32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddPackedFixed32(uint value) {

+        PrepareBuilder();

         result.packedFixed32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangePackedFixed32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.packedFixed32_.Add(values);

         return this;

       }

       public Builder ClearPackedFixed32() {

+        PrepareBuilder();

         result.packedFixed32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> PackedFixed64List {

-        get { return result.packedFixed64_; }

+        get { return PrepareBuilder().packedFixed64_; }

       }

       public int PackedFixed64Count {

         get { return result.PackedFixed64Count; }

@@ -6998,26 +7402,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetPackedFixed64(int index, ulong value) {

+        PrepareBuilder();

         result.packedFixed64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddPackedFixed64(ulong value) {

+        PrepareBuilder();

         result.packedFixed64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangePackedFixed64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.packedFixed64_.Add(values);

         return this;

       }

       public Builder ClearPackedFixed64() {

+        PrepareBuilder();

         result.packedFixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> PackedSfixed32List {

-        get { return result.packedSfixed32_; }

+        get { return PrepareBuilder().packedSfixed32_; }

       }

       public int PackedSfixed32Count {

         get { return result.PackedSfixed32Count; }

@@ -7026,24 +7434,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedSfixed32(index);

       }

       public Builder SetPackedSfixed32(int index, int value) {

+        PrepareBuilder();

         result.packedSfixed32_[index] = value;

         return this;

       }

       public Builder AddPackedSfixed32(int value) {

+        PrepareBuilder();

         result.packedSfixed32_.Add(value);

         return this;

       }

       public Builder AddRangePackedSfixed32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.packedSfixed32_.Add(values);

         return this;

       }

       public Builder ClearPackedSfixed32() {

+        PrepareBuilder();

         result.packedSfixed32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> PackedSfixed64List {

-        get { return result.packedSfixed64_; }

+        get { return PrepareBuilder().packedSfixed64_; }

       }

       public int PackedSfixed64Count {

         get { return result.PackedSfixed64Count; }

@@ -7052,24 +7464,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedSfixed64(index);

       }

       public Builder SetPackedSfixed64(int index, long value) {

+        PrepareBuilder();

         result.packedSfixed64_[index] = value;

         return this;

       }

       public Builder AddPackedSfixed64(long value) {

+        PrepareBuilder();

         result.packedSfixed64_.Add(value);

         return this;

       }

       public Builder AddRangePackedSfixed64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.packedSfixed64_.Add(values);

         return this;

       }

       public Builder ClearPackedSfixed64() {

+        PrepareBuilder();

         result.packedSfixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<float> PackedFloatList {

-        get { return result.packedFloat_; }

+        get { return PrepareBuilder().packedFloat_; }

       }

       public int PackedFloatCount {

         get { return result.PackedFloatCount; }

@@ -7078,24 +7494,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedFloat(index);

       }

       public Builder SetPackedFloat(int index, float value) {

+        PrepareBuilder();

         result.packedFloat_[index] = value;

         return this;

       }

       public Builder AddPackedFloat(float value) {

+        PrepareBuilder();

         result.packedFloat_.Add(value);

         return this;

       }

       public Builder AddRangePackedFloat(scg::IEnumerable<float> values) {

+        PrepareBuilder();

         result.packedFloat_.Add(values);

         return this;

       }

       public Builder ClearPackedFloat() {

+        PrepareBuilder();

         result.packedFloat_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<double> PackedDoubleList {

-        get { return result.packedDouble_; }

+        get { return PrepareBuilder().packedDouble_; }

       }

       public int PackedDoubleCount {

         get { return result.PackedDoubleCount; }

@@ -7104,24 +7524,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedDouble(index);

       }

       public Builder SetPackedDouble(int index, double value) {

+        PrepareBuilder();

         result.packedDouble_[index] = value;

         return this;

       }

       public Builder AddPackedDouble(double value) {

+        PrepareBuilder();

         result.packedDouble_.Add(value);

         return this;

       }

       public Builder AddRangePackedDouble(scg::IEnumerable<double> values) {

+        PrepareBuilder();

         result.packedDouble_.Add(values);

         return this;

       }

       public Builder ClearPackedDouble() {

+        PrepareBuilder();

         result.packedDouble_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<bool> PackedBoolList {

-        get { return result.packedBool_; }

+        get { return PrepareBuilder().packedBool_; }

       }

       public int PackedBoolCount {

         get { return result.PackedBoolCount; }

@@ -7130,24 +7554,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedBool(index);

       }

       public Builder SetPackedBool(int index, bool value) {

+        PrepareBuilder();

         result.packedBool_[index] = value;

         return this;

       }

       public Builder AddPackedBool(bool value) {

+        PrepareBuilder();

         result.packedBool_.Add(value);

         return this;

       }

       public Builder AddRangePackedBool(scg::IEnumerable<bool> values) {

+        PrepareBuilder();

         result.packedBool_.Add(values);

         return this;

       }

       public Builder ClearPackedBool() {

+        PrepareBuilder();

         result.packedBool_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite> PackedEnumList {

-        get { return result.packedEnum_; }

+        get { return PrepareBuilder().packedEnum_; }

       }

       public int PackedEnumCount {

         get { return result.PackedEnumCount; }

@@ -7156,18 +7584,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedEnum(index);

       }

       public Builder SetPackedEnum(int index, global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite value) {

+        PrepareBuilder();

         result.packedEnum_[index] = value;

         return this;

       }

       public Builder AddPackedEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite value) {

+        PrepareBuilder();

         result.packedEnum_.Add(value);

         return this;

       }

       public Builder AddRangePackedEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite> values) {

+        PrepareBuilder();

         result.packedEnum_.Add(values);

         return this;

       }

       public Builder ClearPackedEnum() {

+        PrepareBuilder();

         result.packedEnum_.Clear();

         return this;

       }

@@ -7672,7 +8104,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestUnpackedTypesLite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -7682,21 +8114,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestUnpackedTypesLite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestUnpackedTypesLite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestUnpackedTypesLite result = new TestUnpackedTypesLite();

+      bool builderIsReadOnly;

+      TestUnpackedTypesLite result;

+      

+      private TestUnpackedTypesLite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestUnpackedTypesLite original = result;

+          result = new TestUnpackedTypesLite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestUnpackedTypesLite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestUnpackedTypesLite();

+        result = DefaultInstance ?? new TestUnpackedTypesLite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override TestUnpackedTypesLite DefaultInstanceForType {

@@ -7704,8 +8163,8 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestUnpackedTypesLite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.unpackedInt32_.MakeReadOnly();

         result.unpackedInt64_.MakeReadOnly();

@@ -7721,9 +8180,8 @@ namespace Google.ProtocolBuffers.TestProtos {
         result.unpackedDouble_.MakeReadOnly();

         result.unpackedBool_.MakeReadOnly();

         result.unpackedEnum_.MakeReadOnly();

-        TestUnpackedTypesLite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -7737,6 +8195,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestUnpackedTypesLite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestUnpackedTypesLite.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.unpackedInt32_.Count != 0) {

           result.unpackedInt32_.Add(other.unpackedInt32_);

         }

@@ -7787,6 +8246,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -7889,7 +8349,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       

       public pbc::IPopsicleList<int> UnpackedInt32List {

-        get { return result.unpackedInt32_; }

+        get { return PrepareBuilder().unpackedInt32_; }

       }

       public int UnpackedInt32Count {

         get { return result.UnpackedInt32Count; }

@@ -7898,24 +8358,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedInt32(index);

       }

       public Builder SetUnpackedInt32(int index, int value) {

+        PrepareBuilder();

         result.unpackedInt32_[index] = value;

         return this;

       }

       public Builder AddUnpackedInt32(int value) {

+        PrepareBuilder();

         result.unpackedInt32_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedInt32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.unpackedInt32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedInt32() {

+        PrepareBuilder();

         result.unpackedInt32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> UnpackedInt64List {

-        get { return result.unpackedInt64_; }

+        get { return PrepareBuilder().unpackedInt64_; }

       }

       public int UnpackedInt64Count {

         get { return result.UnpackedInt64Count; }

@@ -7924,25 +8388,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedInt64(index);

       }

       public Builder SetUnpackedInt64(int index, long value) {

+        PrepareBuilder();

         result.unpackedInt64_[index] = value;

         return this;

       }

       public Builder AddUnpackedInt64(long value) {

+        PrepareBuilder();

         result.unpackedInt64_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedInt64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.unpackedInt64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedInt64() {

+        PrepareBuilder();

         result.unpackedInt64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> UnpackedUint32List {

-        get { return result.unpackedUint32_; }

+        get { return PrepareBuilder().unpackedUint32_; }

       }

       public int UnpackedUint32Count {

         get { return result.UnpackedUint32Count; }

@@ -7953,27 +8421,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetUnpackedUint32(int index, uint value) {

+        PrepareBuilder();

         result.unpackedUint32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddUnpackedUint32(uint value) {

+        PrepareBuilder();

         result.unpackedUint32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeUnpackedUint32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.unpackedUint32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedUint32() {

+        PrepareBuilder();

         result.unpackedUint32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> UnpackedUint64List {

-        get { return result.unpackedUint64_; }

+        get { return PrepareBuilder().unpackedUint64_; }

       }

       public int UnpackedUint64Count {

         get { return result.UnpackedUint64Count; }

@@ -7984,26 +8456,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetUnpackedUint64(int index, ulong value) {

+        PrepareBuilder();

         result.unpackedUint64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddUnpackedUint64(ulong value) {

+        PrepareBuilder();

         result.unpackedUint64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeUnpackedUint64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.unpackedUint64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedUint64() {

+        PrepareBuilder();

         result.unpackedUint64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> UnpackedSint32List {

-        get { return result.unpackedSint32_; }

+        get { return PrepareBuilder().unpackedSint32_; }

       }

       public int UnpackedSint32Count {

         get { return result.UnpackedSint32Count; }

@@ -8012,24 +8488,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedSint32(index);

       }

       public Builder SetUnpackedSint32(int index, int value) {

+        PrepareBuilder();

         result.unpackedSint32_[index] = value;

         return this;

       }

       public Builder AddUnpackedSint32(int value) {

+        PrepareBuilder();

         result.unpackedSint32_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedSint32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.unpackedSint32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedSint32() {

+        PrepareBuilder();

         result.unpackedSint32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> UnpackedSint64List {

-        get { return result.unpackedSint64_; }

+        get { return PrepareBuilder().unpackedSint64_; }

       }

       public int UnpackedSint64Count {

         get { return result.UnpackedSint64Count; }

@@ -8038,25 +8518,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedSint64(index);

       }

       public Builder SetUnpackedSint64(int index, long value) {

+        PrepareBuilder();

         result.unpackedSint64_[index] = value;

         return this;

       }

       public Builder AddUnpackedSint64(long value) {

+        PrepareBuilder();

         result.unpackedSint64_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedSint64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.unpackedSint64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedSint64() {

+        PrepareBuilder();

         result.unpackedSint64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> UnpackedFixed32List {

-        get { return result.unpackedFixed32_; }

+        get { return PrepareBuilder().unpackedFixed32_; }

       }

       public int UnpackedFixed32Count {

         get { return result.UnpackedFixed32Count; }

@@ -8067,27 +8551,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetUnpackedFixed32(int index, uint value) {

+        PrepareBuilder();

         result.unpackedFixed32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddUnpackedFixed32(uint value) {

+        PrepareBuilder();

         result.unpackedFixed32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeUnpackedFixed32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.unpackedFixed32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedFixed32() {

+        PrepareBuilder();

         result.unpackedFixed32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> UnpackedFixed64List {

-        get { return result.unpackedFixed64_; }

+        get { return PrepareBuilder().unpackedFixed64_; }

       }

       public int UnpackedFixed64Count {

         get { return result.UnpackedFixed64Count; }

@@ -8098,26 +8586,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetUnpackedFixed64(int index, ulong value) {

+        PrepareBuilder();

         result.unpackedFixed64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddUnpackedFixed64(ulong value) {

+        PrepareBuilder();

         result.unpackedFixed64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeUnpackedFixed64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.unpackedFixed64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedFixed64() {

+        PrepareBuilder();

         result.unpackedFixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> UnpackedSfixed32List {

-        get { return result.unpackedSfixed32_; }

+        get { return PrepareBuilder().unpackedSfixed32_; }

       }

       public int UnpackedSfixed32Count {

         get { return result.UnpackedSfixed32Count; }

@@ -8126,24 +8618,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedSfixed32(index);

       }

       public Builder SetUnpackedSfixed32(int index, int value) {

+        PrepareBuilder();

         result.unpackedSfixed32_[index] = value;

         return this;

       }

       public Builder AddUnpackedSfixed32(int value) {

+        PrepareBuilder();

         result.unpackedSfixed32_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedSfixed32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.unpackedSfixed32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedSfixed32() {

+        PrepareBuilder();

         result.unpackedSfixed32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> UnpackedSfixed64List {

-        get { return result.unpackedSfixed64_; }

+        get { return PrepareBuilder().unpackedSfixed64_; }

       }

       public int UnpackedSfixed64Count {

         get { return result.UnpackedSfixed64Count; }

@@ -8152,24 +8648,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedSfixed64(index);

       }

       public Builder SetUnpackedSfixed64(int index, long value) {

+        PrepareBuilder();

         result.unpackedSfixed64_[index] = value;

         return this;

       }

       public Builder AddUnpackedSfixed64(long value) {

+        PrepareBuilder();

         result.unpackedSfixed64_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedSfixed64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.unpackedSfixed64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedSfixed64() {

+        PrepareBuilder();

         result.unpackedSfixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<float> UnpackedFloatList {

-        get { return result.unpackedFloat_; }

+        get { return PrepareBuilder().unpackedFloat_; }

       }

       public int UnpackedFloatCount {

         get { return result.UnpackedFloatCount; }

@@ -8178,24 +8678,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedFloat(index);

       }

       public Builder SetUnpackedFloat(int index, float value) {

+        PrepareBuilder();

         result.unpackedFloat_[index] = value;

         return this;

       }

       public Builder AddUnpackedFloat(float value) {

+        PrepareBuilder();

         result.unpackedFloat_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedFloat(scg::IEnumerable<float> values) {

+        PrepareBuilder();

         result.unpackedFloat_.Add(values);

         return this;

       }

       public Builder ClearUnpackedFloat() {

+        PrepareBuilder();

         result.unpackedFloat_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<double> UnpackedDoubleList {

-        get { return result.unpackedDouble_; }

+        get { return PrepareBuilder().unpackedDouble_; }

       }

       public int UnpackedDoubleCount {

         get { return result.UnpackedDoubleCount; }

@@ -8204,24 +8708,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedDouble(index);

       }

       public Builder SetUnpackedDouble(int index, double value) {

+        PrepareBuilder();

         result.unpackedDouble_[index] = value;

         return this;

       }

       public Builder AddUnpackedDouble(double value) {

+        PrepareBuilder();

         result.unpackedDouble_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedDouble(scg::IEnumerable<double> values) {

+        PrepareBuilder();

         result.unpackedDouble_.Add(values);

         return this;

       }

       public Builder ClearUnpackedDouble() {

+        PrepareBuilder();

         result.unpackedDouble_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<bool> UnpackedBoolList {

-        get { return result.unpackedBool_; }

+        get { return PrepareBuilder().unpackedBool_; }

       }

       public int UnpackedBoolCount {

         get { return result.UnpackedBoolCount; }

@@ -8230,24 +8738,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedBool(index);

       }

       public Builder SetUnpackedBool(int index, bool value) {

+        PrepareBuilder();

         result.unpackedBool_[index] = value;

         return this;

       }

       public Builder AddUnpackedBool(bool value) {

+        PrepareBuilder();

         result.unpackedBool_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedBool(scg::IEnumerable<bool> values) {

+        PrepareBuilder();

         result.unpackedBool_.Add(values);

         return this;

       }

       public Builder ClearUnpackedBool() {

+        PrepareBuilder();

         result.unpackedBool_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite> UnpackedEnumList {

-        get { return result.unpackedEnum_; }

+        get { return PrepareBuilder().unpackedEnum_; }

       }

       public int UnpackedEnumCount {

         get { return result.UnpackedEnumCount; }

@@ -8256,18 +8768,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedEnum(index);

       }

       public Builder SetUnpackedEnum(int index, global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite value) {

+        PrepareBuilder();

         result.unpackedEnum_[index] = value;

         return this;

       }

       public Builder AddUnpackedEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite value) {

+        PrepareBuilder();

         result.unpackedEnum_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignEnumLite> values) {

+        PrepareBuilder();

         result.unpackedEnum_.Add(values);

         return this;

       }

       public Builder ClearUnpackedEnum() {

+        PrepareBuilder();

         result.unpackedEnum_.Clear();

         return this;

       }

@@ -8377,7 +8893,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestAllExtensionsLite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -8387,21 +8903,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestAllExtensionsLite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestAllExtensionsLite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestAllExtensionsLite result = new TestAllExtensionsLite();

+      bool builderIsReadOnly;

+      TestAllExtensionsLite result;

+      

+      private TestAllExtensionsLite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestAllExtensionsLite original = result;

+          result = new TestAllExtensionsLite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestAllExtensionsLite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestAllExtensionsLite();

+        result = DefaultInstance ?? new TestAllExtensionsLite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override TestAllExtensionsLite DefaultInstanceForType {

@@ -8409,12 +8952,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestAllExtensionsLite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestAllExtensionsLite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -8428,6 +8970,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestAllExtensionsLite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestAllExtensionsLite.DefaultInstance) return this;

+        PrepareBuilder();

           this.MergeExtensionFields(other);

         return this;

       }

@@ -8437,6 +8980,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -8584,7 +9128,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(OptionalGroup_extension_lite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -8594,21 +9138,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new OptionalGroup_extension_lite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(OptionalGroup_extension_lite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      OptionalGroup_extension_lite result;

+      

+      private OptionalGroup_extension_lite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          OptionalGroup_extension_lite original = result;

+          result = new OptionalGroup_extension_lite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      OptionalGroup_extension_lite result = new OptionalGroup_extension_lite();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override OptionalGroup_extension_lite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new OptionalGroup_extension_lite();

+        result = DefaultInstance ?? new OptionalGroup_extension_lite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override OptionalGroup_extension_lite DefaultInstanceForType {

@@ -8616,12 +9187,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override OptionalGroup_extension_lite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        OptionalGroup_extension_lite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -8635,6 +9205,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(OptionalGroup_extension_lite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.OptionalGroup_extension_lite.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           A = other.A;

         }

@@ -8646,6 +9217,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -8688,11 +9260,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetA(value); }

       }

       public Builder SetA(int value) {

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = 0;

         return this;

@@ -8815,7 +9389,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(RepeatedGroup_extension_lite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -8825,21 +9399,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new RepeatedGroup_extension_lite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(RepeatedGroup_extension_lite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      RepeatedGroup_extension_lite result;

+      

+      private RepeatedGroup_extension_lite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          RepeatedGroup_extension_lite original = result;

+          result = new RepeatedGroup_extension_lite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      RepeatedGroup_extension_lite result = new RepeatedGroup_extension_lite();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override RepeatedGroup_extension_lite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new RepeatedGroup_extension_lite();

+        result = DefaultInstance ?? new RepeatedGroup_extension_lite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override RepeatedGroup_extension_lite DefaultInstanceForType {

@@ -8847,12 +9448,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override RepeatedGroup_extension_lite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        RepeatedGroup_extension_lite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -8866,6 +9466,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(RepeatedGroup_extension_lite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.RepeatedGroup_extension_lite.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           A = other.A;

         }

@@ -8877,6 +9478,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -8919,11 +9521,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetA(value); }

       }

       public Builder SetA(int value) {

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = 0;

         return this;

@@ -9034,7 +9638,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestPackedExtensionsLite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -9044,21 +9648,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestPackedExtensionsLite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestPackedExtensionsLite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestPackedExtensionsLite result = new TestPackedExtensionsLite();

+      bool builderIsReadOnly;

+      TestPackedExtensionsLite result;

+      

+      private TestPackedExtensionsLite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestPackedExtensionsLite original = result;

+          result = new TestPackedExtensionsLite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestPackedExtensionsLite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestPackedExtensionsLite();

+        result = DefaultInstance ?? new TestPackedExtensionsLite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override TestPackedExtensionsLite DefaultInstanceForType {

@@ -9066,12 +9697,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestPackedExtensionsLite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestPackedExtensionsLite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -9085,6 +9715,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestPackedExtensionsLite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestPackedExtensionsLite.DefaultInstance) return this;

+        PrepareBuilder();

           this.MergeExtensionFields(other);

         return this;

       }

@@ -9094,6 +9725,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -9229,7 +9861,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestUnpackedExtensionsLite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -9239,21 +9871,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestUnpackedExtensionsLite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestUnpackedExtensionsLite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestUnpackedExtensionsLite result;

       

-      TestUnpackedExtensionsLite result = new TestUnpackedExtensionsLite();

+      private TestUnpackedExtensionsLite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestUnpackedExtensionsLite original = result;

+          result = new TestUnpackedExtensionsLite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestUnpackedExtensionsLite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestUnpackedExtensionsLite();

+        result = DefaultInstance ?? new TestUnpackedExtensionsLite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override TestUnpackedExtensionsLite DefaultInstanceForType {

@@ -9261,12 +9920,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestUnpackedExtensionsLite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestUnpackedExtensionsLite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -9280,6 +9938,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestUnpackedExtensionsLite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestUnpackedExtensionsLite.DefaultInstance) return this;

+        PrepareBuilder();

           this.MergeExtensionFields(other);

         return this;

       }

@@ -9289,6 +9948,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -9419,7 +10079,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestNestedExtensionLite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -9429,21 +10089,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestNestedExtensionLite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestNestedExtensionLite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestNestedExtensionLite result;

+      

+      private TestNestedExtensionLite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestNestedExtensionLite original = result;

+          result = new TestNestedExtensionLite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestNestedExtensionLite result = new TestNestedExtensionLite();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestNestedExtensionLite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestNestedExtensionLite();

+        result = DefaultInstance ?? new TestNestedExtensionLite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override TestNestedExtensionLite DefaultInstanceForType {

@@ -9451,12 +10138,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestNestedExtensionLite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestNestedExtensionLite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -9470,6 +10156,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestNestedExtensionLite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestNestedExtensionLite.DefaultInstance) return this;

+        PrepareBuilder();

         return this;

       }

       

@@ -9478,6 +10165,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -9627,7 +10315,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestDeprecatedLite prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -9637,21 +10325,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestDeprecatedLite();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestDeprecatedLite cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestDeprecatedLite result = new TestDeprecatedLite();

+      bool builderIsReadOnly;

+      TestDeprecatedLite result;

+      

+      private TestDeprecatedLite PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestDeprecatedLite original = result;

+          result = new TestDeprecatedLite();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestDeprecatedLite MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestDeprecatedLite();

+        result = DefaultInstance ?? new TestDeprecatedLite();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override TestDeprecatedLite DefaultInstanceForType {

@@ -9659,12 +10374,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestDeprecatedLite BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestDeprecatedLite returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessageLite other) {

@@ -9678,6 +10392,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestDeprecatedLite other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestDeprecatedLite.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasDeprecatedField) {

           DeprecatedField = other.DeprecatedField;

         }

@@ -9689,6 +10404,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         uint tag;

         string field_name;

         while (input.ReadTag(out tag, out field_name)) {

@@ -9734,12 +10450,14 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.ObsoleteAttribute()]

       public Builder SetDeprecatedField(int value) {

+        PrepareBuilder();

         result.hasDeprecatedField = true;

         result.deprecatedField_ = value;

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder ClearDeprecatedField() {

+        PrepareBuilder();

         result.hasDeprecatedField = false;

         result.deprecatedField_ = 0;

         return this;

diff --git a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestProtoFile.cs b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestProtoFile.cs
index 86616743..547d712a 100644
--- a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestProtoFile.cs
+++ b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestProtoFile.cs
@@ -1262,7 +1262,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(NestedMessage prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1272,21 +1272,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new NestedMessage();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(NestedMessage cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          NestedMessage result;

+          

+          private NestedMessage PrepareBuilder() {

+            if (builderIsReadOnly) {

+              NestedMessage original = result;

+              result = new NestedMessage();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

           

-          NestedMessage result = new NestedMessage();

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override NestedMessage MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new NestedMessage();

+            result = DefaultInstance ?? new NestedMessage();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -1298,12 +1325,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override NestedMessage BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            NestedMessage returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -1317,6 +1343,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(NestedMessage other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasBb) {

               Bb = other.Bb;

             }

@@ -1329,6 +1356,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -1384,11 +1412,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetBb(value); }

           }

           public Builder SetBb(int value) {

+            PrepareBuilder();

             result.hasBb = true;

             result.bb_ = value;

             return this;

           }

           public Builder ClearBb() {

+            PrepareBuilder();

             result.hasBb = false;

             result.bb_ = 0;

             return this;

@@ -1502,7 +1532,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(OptionalGroup prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1512,21 +1542,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new OptionalGroup();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(OptionalGroup cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          OptionalGroup result;

+          

+          private OptionalGroup PrepareBuilder() {

+            if (builderIsReadOnly) {

+              OptionalGroup original = result;

+              result = new OptionalGroup();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

           

-          OptionalGroup result = new OptionalGroup();

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override OptionalGroup MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new OptionalGroup();

+            result = DefaultInstance ?? new OptionalGroup();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -1538,12 +1595,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override OptionalGroup BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            OptionalGroup returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -1557,6 +1613,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(OptionalGroup other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasA) {

               A = other.A;

             }

@@ -1569,6 +1626,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -1624,11 +1682,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetA(value); }

           }

           public Builder SetA(int value) {

+            PrepareBuilder();

             result.hasA = true;

             result.a_ = value;

             return this;

           }

           public Builder ClearA() {

+            PrepareBuilder();

             result.hasA = false;

             result.a_ = 0;

             return this;

@@ -1742,7 +1802,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(RepeatedGroup prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -1752,21 +1812,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new RepeatedGroup();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(RepeatedGroup cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          RepeatedGroup result;

           

-          RepeatedGroup result = new RepeatedGroup();

+          private RepeatedGroup PrepareBuilder() {

+            if (builderIsReadOnly) {

+              RepeatedGroup original = result;

+              result = new RepeatedGroup();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override RepeatedGroup MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new RepeatedGroup();

+            result = DefaultInstance ?? new RepeatedGroup();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -1778,12 +1865,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override RepeatedGroup BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            RepeatedGroup returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -1797,6 +1883,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(RepeatedGroup other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasA) {

               A = other.A;

             }

@@ -1809,6 +1896,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -1864,11 +1952,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetA(value); }

           }

           public Builder SetA(int value) {

+            PrepareBuilder();

             result.hasA = true;

             result.a_ = value;

             return this;

           }

           public Builder ClearA() {

+            PrepareBuilder();

             result.hasA = false;

             result.a_ = 0;

             return this;

@@ -3185,7 +3275,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestAllTypes prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -3195,21 +3285,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestAllTypes();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestAllTypes cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestAllTypes result;

+      

+      private TestAllTypes PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestAllTypes original = result;

+          result = new TestAllTypes();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestAllTypes result = new TestAllTypes();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestAllTypes MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestAllTypes();

+        result = DefaultInstance ?? new TestAllTypes();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -3221,8 +3338,8 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestAllTypes BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.repeatedInt32_.MakeReadOnly();

         result.repeatedInt64_.MakeReadOnly();

@@ -3248,9 +3365,8 @@ namespace Google.ProtocolBuffers.TestProtos {
         result.repeatedImportEnum_.MakeReadOnly();

         result.repeatedStringPiece_.MakeReadOnly();

         result.repeatedCord_.MakeReadOnly();

-        TestAllTypes returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -3264,6 +3380,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestAllTypes other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestAllTypes.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasOptionalInt32) {

           OptionalInt32 = other.OptionalInt32;

         }

@@ -3477,6 +3594,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -3911,11 +4029,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalInt32(value); }

       }

       public Builder SetOptionalInt32(int value) {

+        PrepareBuilder();

         result.hasOptionalInt32 = true;

         result.optionalInt32_ = value;

         return this;

       }

       public Builder ClearOptionalInt32() {

+        PrepareBuilder();

         result.hasOptionalInt32 = false;

         result.optionalInt32_ = 0;

         return this;

@@ -3929,11 +4049,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalInt64(value); }

       }

       public Builder SetOptionalInt64(long value) {

+        PrepareBuilder();

         result.hasOptionalInt64 = true;

         result.optionalInt64_ = value;

         return this;

       }

       public Builder ClearOptionalInt64() {

+        PrepareBuilder();

         result.hasOptionalInt64 = false;

         result.optionalInt64_ = 0L;

         return this;

@@ -3949,11 +4071,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetOptionalUint32(uint value) {

+        PrepareBuilder();

         result.hasOptionalUint32 = true;

         result.optionalUint32_ = value;

         return this;

       }

       public Builder ClearOptionalUint32() {

+        PrepareBuilder();

         result.hasOptionalUint32 = false;

         result.optionalUint32_ = 0;

         return this;

@@ -3969,11 +4093,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetOptionalUint64(ulong value) {

+        PrepareBuilder();

         result.hasOptionalUint64 = true;

         result.optionalUint64_ = value;

         return this;

       }

       public Builder ClearOptionalUint64() {

+        PrepareBuilder();

         result.hasOptionalUint64 = false;

         result.optionalUint64_ = 0UL;

         return this;

@@ -3987,11 +4113,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalSint32(value); }

       }

       public Builder SetOptionalSint32(int value) {

+        PrepareBuilder();

         result.hasOptionalSint32 = true;

         result.optionalSint32_ = value;

         return this;

       }

       public Builder ClearOptionalSint32() {

+        PrepareBuilder();

         result.hasOptionalSint32 = false;

         result.optionalSint32_ = 0;

         return this;

@@ -4005,11 +4133,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalSint64(value); }

       }

       public Builder SetOptionalSint64(long value) {

+        PrepareBuilder();

         result.hasOptionalSint64 = true;

         result.optionalSint64_ = value;

         return this;

       }

       public Builder ClearOptionalSint64() {

+        PrepareBuilder();

         result.hasOptionalSint64 = false;

         result.optionalSint64_ = 0;

         return this;

@@ -4025,11 +4155,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetOptionalFixed32(uint value) {

+        PrepareBuilder();

         result.hasOptionalFixed32 = true;

         result.optionalFixed32_ = value;

         return this;

       }

       public Builder ClearOptionalFixed32() {

+        PrepareBuilder();

         result.hasOptionalFixed32 = false;

         result.optionalFixed32_ = 0;

         return this;

@@ -4045,11 +4177,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetOptionalFixed64(ulong value) {

+        PrepareBuilder();

         result.hasOptionalFixed64 = true;

         result.optionalFixed64_ = value;

         return this;

       }

       public Builder ClearOptionalFixed64() {

+        PrepareBuilder();

         result.hasOptionalFixed64 = false;

         result.optionalFixed64_ = 0;

         return this;

@@ -4063,11 +4197,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalSfixed32(value); }

       }

       public Builder SetOptionalSfixed32(int value) {

+        PrepareBuilder();

         result.hasOptionalSfixed32 = true;

         result.optionalSfixed32_ = value;

         return this;

       }

       public Builder ClearOptionalSfixed32() {

+        PrepareBuilder();

         result.hasOptionalSfixed32 = false;

         result.optionalSfixed32_ = 0;

         return this;

@@ -4081,11 +4217,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalSfixed64(value); }

       }

       public Builder SetOptionalSfixed64(long value) {

+        PrepareBuilder();

         result.hasOptionalSfixed64 = true;

         result.optionalSfixed64_ = value;

         return this;

       }

       public Builder ClearOptionalSfixed64() {

+        PrepareBuilder();

         result.hasOptionalSfixed64 = false;

         result.optionalSfixed64_ = 0;

         return this;

@@ -4099,11 +4237,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalFloat(value); }

       }

       public Builder SetOptionalFloat(float value) {

+        PrepareBuilder();

         result.hasOptionalFloat = true;

         result.optionalFloat_ = value;

         return this;

       }

       public Builder ClearOptionalFloat() {

+        PrepareBuilder();

         result.hasOptionalFloat = false;

         result.optionalFloat_ = 0F;

         return this;

@@ -4117,11 +4257,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalDouble(value); }

       }

       public Builder SetOptionalDouble(double value) {

+        PrepareBuilder();

         result.hasOptionalDouble = true;

         result.optionalDouble_ = value;

         return this;

       }

       public Builder ClearOptionalDouble() {

+        PrepareBuilder();

         result.hasOptionalDouble = false;

         result.optionalDouble_ = 0D;

         return this;

@@ -4135,11 +4277,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalBool(value); }

       }

       public Builder SetOptionalBool(bool value) {

+        PrepareBuilder();

         result.hasOptionalBool = true;

         result.optionalBool_ = value;

         return this;

       }

       public Builder ClearOptionalBool() {

+        PrepareBuilder();

         result.hasOptionalBool = false;

         result.optionalBool_ = false;

         return this;

@@ -4154,11 +4298,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalString(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalString = true;

         result.optionalString_ = value;

         return this;

       }

       public Builder ClearOptionalString() {

+        PrepareBuilder();

         result.hasOptionalString = false;

         result.optionalString_ = "";

         return this;

@@ -4173,11 +4319,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalBytes(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalBytes = true;

         result.optionalBytes_ = value;

         return this;

       }

       public Builder ClearOptionalBytes() {

+        PrepareBuilder();

         result.hasOptionalBytes = false;

         result.optionalBytes_ = pb::ByteString.Empty;

         return this;

@@ -4192,18 +4340,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalGroup = true;

         result.optionalGroup_ = value;

         return this;

       }

       public Builder SetOptionalGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalGroup = true;

         result.optionalGroup_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalGroup &&

             result.optionalGroup_ != global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup.DefaultInstance) {

             result.optionalGroup_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup.CreateBuilder(result.optionalGroup_).MergeFrom(value).BuildPartial();

@@ -4214,6 +4365,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalGroup() {

+        PrepareBuilder();

         result.hasOptionalGroup = false;

         result.optionalGroup_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup.DefaultInstance;

         return this;

@@ -4228,18 +4380,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalNestedMessage = true;

         result.optionalNestedMessage_ = value;

         return this;

       }

       public Builder SetOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalNestedMessage = true;

         result.optionalNestedMessage_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalNestedMessage &&

             result.optionalNestedMessage_ != global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance) {

             result.optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.CreateBuilder(result.optionalNestedMessage_).MergeFrom(value).BuildPartial();

@@ -4250,6 +4405,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalNestedMessage() {

+        PrepareBuilder();

         result.hasOptionalNestedMessage = false;

         result.optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance;

         return this;

@@ -4264,18 +4420,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalForeignMessage = true;

         result.optionalForeignMessage_ = value;

         return this;

       }

       public Builder SetOptionalForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalForeignMessage = true;

         result.optionalForeignMessage_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalForeignMessage &&

             result.optionalForeignMessage_ != global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance) {

             result.optionalForeignMessage_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.CreateBuilder(result.optionalForeignMessage_).MergeFrom(value).BuildPartial();

@@ -4286,6 +4445,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalForeignMessage() {

+        PrepareBuilder();

         result.hasOptionalForeignMessage = false;

         result.optionalForeignMessage_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance;

         return this;

@@ -4300,18 +4460,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalImportMessage = true;

         result.optionalImportMessage_ = value;

         return this;

       }

       public Builder SetOptionalImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalImportMessage = true;

         result.optionalImportMessage_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalImportMessage &&

             result.optionalImportMessage_ != global::Google.ProtocolBuffers.TestProtos.ImportMessage.DefaultInstance) {

             result.optionalImportMessage_ = global::Google.ProtocolBuffers.TestProtos.ImportMessage.CreateBuilder(result.optionalImportMessage_).MergeFrom(value).BuildPartial();

@@ -4322,6 +4485,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalImportMessage() {

+        PrepareBuilder();

         result.hasOptionalImportMessage = false;

         result.optionalImportMessage_ = global::Google.ProtocolBuffers.TestProtos.ImportMessage.DefaultInstance;

         return this;

@@ -4335,11 +4499,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalNestedEnum(value); }

       }

       public Builder SetOptionalNestedEnum(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum value) {

+        PrepareBuilder();

         result.hasOptionalNestedEnum = true;

         result.optionalNestedEnum_ = value;

         return this;

       }

       public Builder ClearOptionalNestedEnum() {

+        PrepareBuilder();

         result.hasOptionalNestedEnum = false;

         result.optionalNestedEnum_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum.FOO;

         return this;

@@ -4353,11 +4519,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalForeignEnum(value); }

       }

       public Builder SetOptionalForeignEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.hasOptionalForeignEnum = true;

         result.optionalForeignEnum_ = value;

         return this;

       }

       public Builder ClearOptionalForeignEnum() {

+        PrepareBuilder();

         result.hasOptionalForeignEnum = false;

         result.optionalForeignEnum_ = global::Google.ProtocolBuffers.TestProtos.ForeignEnum.FOREIGN_FOO;

         return this;

@@ -4371,11 +4539,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalImportEnum(value); }

       }

       public Builder SetOptionalImportEnum(global::Google.ProtocolBuffers.TestProtos.ImportEnum value) {

+        PrepareBuilder();

         result.hasOptionalImportEnum = true;

         result.optionalImportEnum_ = value;

         return this;

       }

       public Builder ClearOptionalImportEnum() {

+        PrepareBuilder();

         result.hasOptionalImportEnum = false;

         result.optionalImportEnum_ = global::Google.ProtocolBuffers.TestProtos.ImportEnum.IMPORT_FOO;

         return this;

@@ -4390,11 +4560,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalStringPiece(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalStringPiece = true;

         result.optionalStringPiece_ = value;

         return this;

       }

       public Builder ClearOptionalStringPiece() {

+        PrepareBuilder();

         result.hasOptionalStringPiece = false;

         result.optionalStringPiece_ = "";

         return this;

@@ -4409,18 +4581,20 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalCord(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalCord = true;

         result.optionalCord_ = value;

         return this;

       }

       public Builder ClearOptionalCord() {

+        PrepareBuilder();

         result.hasOptionalCord = false;

         result.optionalCord_ = "";

         return this;

       }

       

       public pbc::IPopsicleList<int> RepeatedInt32List {

-        get { return result.repeatedInt32_; }

+        get { return PrepareBuilder().repeatedInt32_; }

       }

       public int RepeatedInt32Count {

         get { return result.RepeatedInt32Count; }

@@ -4429,24 +4603,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedInt32(index);

       }

       public Builder SetRepeatedInt32(int index, int value) {

+        PrepareBuilder();

         result.repeatedInt32_[index] = value;

         return this;

       }

       public Builder AddRepeatedInt32(int value) {

+        PrepareBuilder();

         result.repeatedInt32_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedInt32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.repeatedInt32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedInt32() {

+        PrepareBuilder();

         result.repeatedInt32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> RepeatedInt64List {

-        get { return result.repeatedInt64_; }

+        get { return PrepareBuilder().repeatedInt64_; }

       }

       public int RepeatedInt64Count {

         get { return result.RepeatedInt64Count; }

@@ -4455,25 +4633,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedInt64(index);

       }

       public Builder SetRepeatedInt64(int index, long value) {

+        PrepareBuilder();

         result.repeatedInt64_[index] = value;

         return this;

       }

       public Builder AddRepeatedInt64(long value) {

+        PrepareBuilder();

         result.repeatedInt64_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedInt64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.repeatedInt64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedInt64() {

+        PrepareBuilder();

         result.repeatedInt64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> RepeatedUint32List {

-        get { return result.repeatedUint32_; }

+        get { return PrepareBuilder().repeatedUint32_; }

       }

       public int RepeatedUint32Count {

         get { return result.RepeatedUint32Count; }

@@ -4484,27 +4666,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedUint32(int index, uint value) {

+        PrepareBuilder();

         result.repeatedUint32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedUint32(uint value) {

+        PrepareBuilder();

         result.repeatedUint32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedUint32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.repeatedUint32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedUint32() {

+        PrepareBuilder();

         result.repeatedUint32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> RepeatedUint64List {

-        get { return result.repeatedUint64_; }

+        get { return PrepareBuilder().repeatedUint64_; }

       }

       public int RepeatedUint64Count {

         get { return result.RepeatedUint64Count; }

@@ -4515,26 +4701,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedUint64(int index, ulong value) {

+        PrepareBuilder();

         result.repeatedUint64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedUint64(ulong value) {

+        PrepareBuilder();

         result.repeatedUint64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedUint64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.repeatedUint64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedUint64() {

+        PrepareBuilder();

         result.repeatedUint64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> RepeatedSint32List {

-        get { return result.repeatedSint32_; }

+        get { return PrepareBuilder().repeatedSint32_; }

       }

       public int RepeatedSint32Count {

         get { return result.RepeatedSint32Count; }

@@ -4543,24 +4733,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedSint32(index);

       }

       public Builder SetRepeatedSint32(int index, int value) {

+        PrepareBuilder();

         result.repeatedSint32_[index] = value;

         return this;

       }

       public Builder AddRepeatedSint32(int value) {

+        PrepareBuilder();

         result.repeatedSint32_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedSint32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.repeatedSint32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedSint32() {

+        PrepareBuilder();

         result.repeatedSint32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> RepeatedSint64List {

-        get { return result.repeatedSint64_; }

+        get { return PrepareBuilder().repeatedSint64_; }

       }

       public int RepeatedSint64Count {

         get { return result.RepeatedSint64Count; }

@@ -4569,25 +4763,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedSint64(index);

       }

       public Builder SetRepeatedSint64(int index, long value) {

+        PrepareBuilder();

         result.repeatedSint64_[index] = value;

         return this;

       }

       public Builder AddRepeatedSint64(long value) {

+        PrepareBuilder();

         result.repeatedSint64_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedSint64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.repeatedSint64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedSint64() {

+        PrepareBuilder();

         result.repeatedSint64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> RepeatedFixed32List {

-        get { return result.repeatedFixed32_; }

+        get { return PrepareBuilder().repeatedFixed32_; }

       }

       public int RepeatedFixed32Count {

         get { return result.RepeatedFixed32Count; }

@@ -4598,27 +4796,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedFixed32(int index, uint value) {

+        PrepareBuilder();

         result.repeatedFixed32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedFixed32(uint value) {

+        PrepareBuilder();

         result.repeatedFixed32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedFixed32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.repeatedFixed32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFixed32() {

+        PrepareBuilder();

         result.repeatedFixed32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> RepeatedFixed64List {

-        get { return result.repeatedFixed64_; }

+        get { return PrepareBuilder().repeatedFixed64_; }

       }

       public int RepeatedFixed64Count {

         get { return result.RepeatedFixed64Count; }

@@ -4629,26 +4831,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedFixed64(int index, ulong value) {

+        PrepareBuilder();

         result.repeatedFixed64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedFixed64(ulong value) {

+        PrepareBuilder();

         result.repeatedFixed64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedFixed64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.repeatedFixed64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFixed64() {

+        PrepareBuilder();

         result.repeatedFixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> RepeatedSfixed32List {

-        get { return result.repeatedSfixed32_; }

+        get { return PrepareBuilder().repeatedSfixed32_; }

       }

       public int RepeatedSfixed32Count {

         get { return result.RepeatedSfixed32Count; }

@@ -4657,24 +4863,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedSfixed32(index);

       }

       public Builder SetRepeatedSfixed32(int index, int value) {

+        PrepareBuilder();

         result.repeatedSfixed32_[index] = value;

         return this;

       }

       public Builder AddRepeatedSfixed32(int value) {

+        PrepareBuilder();

         result.repeatedSfixed32_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedSfixed32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.repeatedSfixed32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedSfixed32() {

+        PrepareBuilder();

         result.repeatedSfixed32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> RepeatedSfixed64List {

-        get { return result.repeatedSfixed64_; }

+        get { return PrepareBuilder().repeatedSfixed64_; }

       }

       public int RepeatedSfixed64Count {

         get { return result.RepeatedSfixed64Count; }

@@ -4683,24 +4893,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedSfixed64(index);

       }

       public Builder SetRepeatedSfixed64(int index, long value) {

+        PrepareBuilder();

         result.repeatedSfixed64_[index] = value;

         return this;

       }

       public Builder AddRepeatedSfixed64(long value) {

+        PrepareBuilder();

         result.repeatedSfixed64_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedSfixed64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.repeatedSfixed64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedSfixed64() {

+        PrepareBuilder();

         result.repeatedSfixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<float> RepeatedFloatList {

-        get { return result.repeatedFloat_; }

+        get { return PrepareBuilder().repeatedFloat_; }

       }

       public int RepeatedFloatCount {

         get { return result.RepeatedFloatCount; }

@@ -4709,24 +4923,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedFloat(index);

       }

       public Builder SetRepeatedFloat(int index, float value) {

+        PrepareBuilder();

         result.repeatedFloat_[index] = value;

         return this;

       }

       public Builder AddRepeatedFloat(float value) {

+        PrepareBuilder();

         result.repeatedFloat_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedFloat(scg::IEnumerable<float> values) {

+        PrepareBuilder();

         result.repeatedFloat_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFloat() {

+        PrepareBuilder();

         result.repeatedFloat_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<double> RepeatedDoubleList {

-        get { return result.repeatedDouble_; }

+        get { return PrepareBuilder().repeatedDouble_; }

       }

       public int RepeatedDoubleCount {

         get { return result.RepeatedDoubleCount; }

@@ -4735,24 +4953,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedDouble(index);

       }

       public Builder SetRepeatedDouble(int index, double value) {

+        PrepareBuilder();

         result.repeatedDouble_[index] = value;

         return this;

       }

       public Builder AddRepeatedDouble(double value) {

+        PrepareBuilder();

         result.repeatedDouble_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedDouble(scg::IEnumerable<double> values) {

+        PrepareBuilder();

         result.repeatedDouble_.Add(values);

         return this;

       }

       public Builder ClearRepeatedDouble() {

+        PrepareBuilder();

         result.repeatedDouble_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<bool> RepeatedBoolList {

-        get { return result.repeatedBool_; }

+        get { return PrepareBuilder().repeatedBool_; }

       }

       public int RepeatedBoolCount {

         get { return result.RepeatedBoolCount; }

@@ -4761,24 +4983,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedBool(index);

       }

       public Builder SetRepeatedBool(int index, bool value) {

+        PrepareBuilder();

         result.repeatedBool_[index] = value;

         return this;

       }

       public Builder AddRepeatedBool(bool value) {

+        PrepareBuilder();

         result.repeatedBool_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedBool(scg::IEnumerable<bool> values) {

+        PrepareBuilder();

         result.repeatedBool_.Add(values);

         return this;

       }

       public Builder ClearRepeatedBool() {

+        PrepareBuilder();

         result.repeatedBool_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedStringList {

-        get { return result.repeatedString_; }

+        get { return PrepareBuilder().repeatedString_; }

       }

       public int RepeatedStringCount {

         get { return result.RepeatedStringCount; }

@@ -4788,25 +5014,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedString(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedString_[index] = value;

         return this;

       }

       public Builder AddRepeatedString(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedString_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedString(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedString_.Add(values);

         return this;

       }

       public Builder ClearRepeatedString() {

+        PrepareBuilder();

         result.repeatedString_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<pb::ByteString> RepeatedBytesList {

-        get { return result.repeatedBytes_; }

+        get { return PrepareBuilder().repeatedBytes_; }

       }

       public int RepeatedBytesCount {

         get { return result.RepeatedBytesCount; }

@@ -4816,25 +5046,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedBytes(int index, pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedBytes_[index] = value;

         return this;

       }

       public Builder AddRepeatedBytes(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedBytes_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedBytes(scg::IEnumerable<pb::ByteString> values) {

+        PrepareBuilder();

         result.repeatedBytes_.Add(values);

         return this;

       }

       public Builder ClearRepeatedBytes() {

+        PrepareBuilder();

         result.repeatedBytes_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup> RepeatedGroupList {

-        get { return result.repeatedGroup_; }

+        get { return PrepareBuilder().repeatedGroup_; }

       }

       public int RepeatedGroupCount {

         get { return result.RepeatedGroupCount; }

@@ -4844,35 +5078,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedGroup(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedGroup_[index] = value;

         return this;

       }

       public Builder SetRepeatedGroup(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedGroup_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedGroup_.Add(value);

         return this;

       }

       public Builder AddRepeatedGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedGroup_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedGroup(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup> values) {

+        PrepareBuilder();

         result.repeatedGroup_.Add(values);

         return this;

       }

       public Builder ClearRepeatedGroup() {

+        PrepareBuilder();

         result.repeatedGroup_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage> RepeatedNestedMessageList {

-        get { return result.repeatedNestedMessage_; }

+        get { return PrepareBuilder().repeatedNestedMessage_; }

       }

       public int RepeatedNestedMessageCount {

         get { return result.RepeatedNestedMessageCount; }

@@ -4882,35 +5122,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedNestedMessage(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedNestedMessage_[index] = value;

         return this;

       }

       public Builder SetRepeatedNestedMessage(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedNestedMessage_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedNestedMessage_.Add(value);

         return this;

       }

       public Builder AddRepeatedNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedNestedMessage_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedNestedMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage> values) {

+        PrepareBuilder();

         result.repeatedNestedMessage_.Add(values);

         return this;

       }

       public Builder ClearRepeatedNestedMessage() {

+        PrepareBuilder();

         result.repeatedNestedMessage_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> RepeatedForeignMessageList {

-        get { return result.repeatedForeignMessage_; }

+        get { return PrepareBuilder().repeatedForeignMessage_; }

       }

       public int RepeatedForeignMessageCount {

         get { return result.RepeatedForeignMessageCount; }

@@ -4920,35 +5166,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedForeignMessage(int index, global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedForeignMessage_[index] = value;

         return this;

       }

       public Builder SetRepeatedForeignMessage(int index, global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedForeignMessage_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedForeignMessage_.Add(value);

         return this;

       }

       public Builder AddRepeatedForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedForeignMessage_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedForeignMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> values) {

+        PrepareBuilder();

         result.repeatedForeignMessage_.Add(values);

         return this;

       }

       public Builder ClearRepeatedForeignMessage() {

+        PrepareBuilder();

         result.repeatedForeignMessage_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ImportMessage> RepeatedImportMessageList {

-        get { return result.repeatedImportMessage_; }

+        get { return PrepareBuilder().repeatedImportMessage_; }

       }

       public int RepeatedImportMessageCount {

         get { return result.RepeatedImportMessageCount; }

@@ -4958,35 +5210,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedImportMessage(int index, global::Google.ProtocolBuffers.TestProtos.ImportMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedImportMessage_[index] = value;

         return this;

       }

       public Builder SetRepeatedImportMessage(int index, global::Google.ProtocolBuffers.TestProtos.ImportMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedImportMessage_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedImportMessage_.Add(value);

         return this;

       }

       public Builder AddRepeatedImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedImportMessage_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedImportMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ImportMessage> values) {

+        PrepareBuilder();

         result.repeatedImportMessage_.Add(values);

         return this;

       }

       public Builder ClearRepeatedImportMessage() {

+        PrepareBuilder();

         result.repeatedImportMessage_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum> RepeatedNestedEnumList {

-        get { return result.repeatedNestedEnum_; }

+        get { return PrepareBuilder().repeatedNestedEnum_; }

       }

       public int RepeatedNestedEnumCount {

         get { return result.RepeatedNestedEnumCount; }

@@ -4995,24 +5253,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedNestedEnum(index);

       }

       public Builder SetRepeatedNestedEnum(int index, global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum value) {

+        PrepareBuilder();

         result.repeatedNestedEnum_[index] = value;

         return this;

       }

       public Builder AddRepeatedNestedEnum(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum value) {

+        PrepareBuilder();

         result.repeatedNestedEnum_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedNestedEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum> values) {

+        PrepareBuilder();

         result.repeatedNestedEnum_.Add(values);

         return this;

       }

       public Builder ClearRepeatedNestedEnum() {

+        PrepareBuilder();

         result.repeatedNestedEnum_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> RepeatedForeignEnumList {

-        get { return result.repeatedForeignEnum_; }

+        get { return PrepareBuilder().repeatedForeignEnum_; }

       }

       public int RepeatedForeignEnumCount {

         get { return result.RepeatedForeignEnumCount; }

@@ -5021,24 +5283,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedForeignEnum(index);

       }

       public Builder SetRepeatedForeignEnum(int index, global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.repeatedForeignEnum_[index] = value;

         return this;

       }

       public Builder AddRepeatedForeignEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.repeatedForeignEnum_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedForeignEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> values) {

+        PrepareBuilder();

         result.repeatedForeignEnum_.Add(values);

         return this;

       }

       public Builder ClearRepeatedForeignEnum() {

+        PrepareBuilder();

         result.repeatedForeignEnum_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ImportEnum> RepeatedImportEnumList {

-        get { return result.repeatedImportEnum_; }

+        get { return PrepareBuilder().repeatedImportEnum_; }

       }

       public int RepeatedImportEnumCount {

         get { return result.RepeatedImportEnumCount; }

@@ -5047,24 +5313,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedImportEnum(index);

       }

       public Builder SetRepeatedImportEnum(int index, global::Google.ProtocolBuffers.TestProtos.ImportEnum value) {

+        PrepareBuilder();

         result.repeatedImportEnum_[index] = value;

         return this;

       }

       public Builder AddRepeatedImportEnum(global::Google.ProtocolBuffers.TestProtos.ImportEnum value) {

+        PrepareBuilder();

         result.repeatedImportEnum_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedImportEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ImportEnum> values) {

+        PrepareBuilder();

         result.repeatedImportEnum_.Add(values);

         return this;

       }

       public Builder ClearRepeatedImportEnum() {

+        PrepareBuilder();

         result.repeatedImportEnum_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedStringPieceList {

-        get { return result.repeatedStringPiece_; }

+        get { return PrepareBuilder().repeatedStringPiece_; }

       }

       public int RepeatedStringPieceCount {

         get { return result.RepeatedStringPieceCount; }

@@ -5074,25 +5344,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedStringPiece(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedStringPiece_[index] = value;

         return this;

       }

       public Builder AddRepeatedStringPiece(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedStringPiece_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedStringPiece(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedStringPiece_.Add(values);

         return this;

       }

       public Builder ClearRepeatedStringPiece() {

+        PrepareBuilder();

         result.repeatedStringPiece_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedCordList {

-        get { return result.repeatedCord_; }

+        get { return PrepareBuilder().repeatedCord_; }

       }

       public int RepeatedCordCount {

         get { return result.RepeatedCordCount; }

@@ -5102,19 +5376,23 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedCord(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedCord_[index] = value;

         return this;

       }

       public Builder AddRepeatedCord(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedCord_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedCord(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedCord_.Add(values);

         return this;

       }

       public Builder ClearRepeatedCord() {

+        PrepareBuilder();

         result.repeatedCord_.Clear();

         return this;

       }

@@ -5127,11 +5405,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultInt32(value); }

       }

       public Builder SetDefaultInt32(int value) {

+        PrepareBuilder();

         result.hasDefaultInt32 = true;

         result.defaultInt32_ = value;

         return this;

       }

       public Builder ClearDefaultInt32() {

+        PrepareBuilder();

         result.hasDefaultInt32 = false;

         result.defaultInt32_ = 41;

         return this;

@@ -5145,11 +5425,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultInt64(value); }

       }

       public Builder SetDefaultInt64(long value) {

+        PrepareBuilder();

         result.hasDefaultInt64 = true;

         result.defaultInt64_ = value;

         return this;

       }

       public Builder ClearDefaultInt64() {

+        PrepareBuilder();

         result.hasDefaultInt64 = false;

         result.defaultInt64_ = 42L;

         return this;

@@ -5165,11 +5447,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetDefaultUint32(uint value) {

+        PrepareBuilder();

         result.hasDefaultUint32 = true;

         result.defaultUint32_ = value;

         return this;

       }

       public Builder ClearDefaultUint32() {

+        PrepareBuilder();

         result.hasDefaultUint32 = false;

         result.defaultUint32_ = 43;

         return this;

@@ -5185,11 +5469,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetDefaultUint64(ulong value) {

+        PrepareBuilder();

         result.hasDefaultUint64 = true;

         result.defaultUint64_ = value;

         return this;

       }

       public Builder ClearDefaultUint64() {

+        PrepareBuilder();

         result.hasDefaultUint64 = false;

         result.defaultUint64_ = 44UL;

         return this;

@@ -5203,11 +5489,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultSint32(value); }

       }

       public Builder SetDefaultSint32(int value) {

+        PrepareBuilder();

         result.hasDefaultSint32 = true;

         result.defaultSint32_ = value;

         return this;

       }

       public Builder ClearDefaultSint32() {

+        PrepareBuilder();

         result.hasDefaultSint32 = false;

         result.defaultSint32_ = -45;

         return this;

@@ -5221,11 +5509,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultSint64(value); }

       }

       public Builder SetDefaultSint64(long value) {

+        PrepareBuilder();

         result.hasDefaultSint64 = true;

         result.defaultSint64_ = value;

         return this;

       }

       public Builder ClearDefaultSint64() {

+        PrepareBuilder();

         result.hasDefaultSint64 = false;

         result.defaultSint64_ = 46;

         return this;

@@ -5241,11 +5531,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetDefaultFixed32(uint value) {

+        PrepareBuilder();

         result.hasDefaultFixed32 = true;

         result.defaultFixed32_ = value;

         return this;

       }

       public Builder ClearDefaultFixed32() {

+        PrepareBuilder();

         result.hasDefaultFixed32 = false;

         result.defaultFixed32_ = 47;

         return this;

@@ -5261,11 +5553,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetDefaultFixed64(ulong value) {

+        PrepareBuilder();

         result.hasDefaultFixed64 = true;

         result.defaultFixed64_ = value;

         return this;

       }

       public Builder ClearDefaultFixed64() {

+        PrepareBuilder();

         result.hasDefaultFixed64 = false;

         result.defaultFixed64_ = 48;

         return this;

@@ -5279,11 +5573,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultSfixed32(value); }

       }

       public Builder SetDefaultSfixed32(int value) {

+        PrepareBuilder();

         result.hasDefaultSfixed32 = true;

         result.defaultSfixed32_ = value;

         return this;

       }

       public Builder ClearDefaultSfixed32() {

+        PrepareBuilder();

         result.hasDefaultSfixed32 = false;

         result.defaultSfixed32_ = 49;

         return this;

@@ -5297,11 +5593,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultSfixed64(value); }

       }

       public Builder SetDefaultSfixed64(long value) {

+        PrepareBuilder();

         result.hasDefaultSfixed64 = true;

         result.defaultSfixed64_ = value;

         return this;

       }

       public Builder ClearDefaultSfixed64() {

+        PrepareBuilder();

         result.hasDefaultSfixed64 = false;

         result.defaultSfixed64_ = -50;

         return this;

@@ -5315,11 +5613,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultFloat(value); }

       }

       public Builder SetDefaultFloat(float value) {

+        PrepareBuilder();

         result.hasDefaultFloat = true;

         result.defaultFloat_ = value;

         return this;

       }

       public Builder ClearDefaultFloat() {

+        PrepareBuilder();

         result.hasDefaultFloat = false;

         result.defaultFloat_ = 51.5F;

         return this;

@@ -5333,11 +5633,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultDouble(value); }

       }

       public Builder SetDefaultDouble(double value) {

+        PrepareBuilder();

         result.hasDefaultDouble = true;

         result.defaultDouble_ = value;

         return this;

       }

       public Builder ClearDefaultDouble() {

+        PrepareBuilder();

         result.hasDefaultDouble = false;

         result.defaultDouble_ = 52000D;

         return this;

@@ -5351,11 +5653,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultBool(value); }

       }

       public Builder SetDefaultBool(bool value) {

+        PrepareBuilder();

         result.hasDefaultBool = true;

         result.defaultBool_ = value;

         return this;

       }

       public Builder ClearDefaultBool() {

+        PrepareBuilder();

         result.hasDefaultBool = false;

         result.defaultBool_ = true;

         return this;

@@ -5370,11 +5674,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetDefaultString(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDefaultString = true;

         result.defaultString_ = value;

         return this;

       }

       public Builder ClearDefaultString() {

+        PrepareBuilder();

         result.hasDefaultString = false;

         result.defaultString_ = "hello";

         return this;

@@ -5389,11 +5695,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetDefaultBytes(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDefaultBytes = true;

         result.defaultBytes_ = value;

         return this;

       }

       public Builder ClearDefaultBytes() {

+        PrepareBuilder();

         result.hasDefaultBytes = false;

         result.defaultBytes_ = (pb::ByteString) global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Descriptor.Fields[62].DefaultValue;

         return this;

@@ -5407,11 +5715,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultNestedEnum(value); }

       }

       public Builder SetDefaultNestedEnum(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum value) {

+        PrepareBuilder();

         result.hasDefaultNestedEnum = true;

         result.defaultNestedEnum_ = value;

         return this;

       }

       public Builder ClearDefaultNestedEnum() {

+        PrepareBuilder();

         result.hasDefaultNestedEnum = false;

         result.defaultNestedEnum_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedEnum.BAR;

         return this;

@@ -5425,11 +5735,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultForeignEnum(value); }

       }

       public Builder SetDefaultForeignEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.hasDefaultForeignEnum = true;

         result.defaultForeignEnum_ = value;

         return this;

       }

       public Builder ClearDefaultForeignEnum() {

+        PrepareBuilder();

         result.hasDefaultForeignEnum = false;

         result.defaultForeignEnum_ = global::Google.ProtocolBuffers.TestProtos.ForeignEnum.FOREIGN_BAR;

         return this;

@@ -5443,11 +5755,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDefaultImportEnum(value); }

       }

       public Builder SetDefaultImportEnum(global::Google.ProtocolBuffers.TestProtos.ImportEnum value) {

+        PrepareBuilder();

         result.hasDefaultImportEnum = true;

         result.defaultImportEnum_ = value;

         return this;

       }

       public Builder ClearDefaultImportEnum() {

+        PrepareBuilder();

         result.hasDefaultImportEnum = false;

         result.defaultImportEnum_ = global::Google.ProtocolBuffers.TestProtos.ImportEnum.IMPORT_BAR;

         return this;

@@ -5462,11 +5776,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetDefaultStringPiece(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDefaultStringPiece = true;

         result.defaultStringPiece_ = value;

         return this;

       }

       public Builder ClearDefaultStringPiece() {

+        PrepareBuilder();

         result.hasDefaultStringPiece = false;

         result.defaultStringPiece_ = "abc";

         return this;

@@ -5481,11 +5797,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetDefaultCord(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDefaultCord = true;

         result.defaultCord_ = value;

         return this;

       }

       public Builder ClearDefaultCord() {

+        PrepareBuilder();

         result.hasDefaultCord = false;

         result.defaultCord_ = "123";

         return this;

@@ -5601,7 +5919,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestDeprecatedFields prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -5611,21 +5929,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestDeprecatedFields();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestDeprecatedFields cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestDeprecatedFields result;

       

-      TestDeprecatedFields result = new TestDeprecatedFields();

+      private TestDeprecatedFields PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestDeprecatedFields original = result;

+          result = new TestDeprecatedFields();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestDeprecatedFields MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestDeprecatedFields();

+        result = DefaultInstance ?? new TestDeprecatedFields();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -5637,12 +5982,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestDeprecatedFields BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestDeprecatedFields returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -5656,6 +6000,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestDeprecatedFields other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestDeprecatedFields.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasDeprecatedInt32) {

           DeprecatedInt32 = other.DeprecatedInt32;

         }

@@ -5668,6 +6013,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -5726,12 +6072,14 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.ObsoleteAttribute()]

       public Builder SetDeprecatedInt32(int value) {

+        PrepareBuilder();

         result.hasDeprecatedInt32 = true;

         result.deprecatedInt32_ = value;

         return this;

       }

       [global::System.ObsoleteAttribute()]

       public Builder ClearDeprecatedInt32() {

+        PrepareBuilder();

         result.hasDeprecatedInt32 = false;

         result.deprecatedInt32_ = 0;

         return this;

@@ -5845,7 +6193,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(ForeignMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -5855,21 +6203,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new ForeignMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(ForeignMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      ForeignMessage result = new ForeignMessage();

+      bool builderIsReadOnly;

+      ForeignMessage result;

+      

+      private ForeignMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          ForeignMessage original = result;

+          result = new ForeignMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override ForeignMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new ForeignMessage();

+        result = DefaultInstance ?? new ForeignMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -5881,12 +6256,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override ForeignMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        ForeignMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -5900,6 +6274,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(ForeignMessage other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasC) {

           C = other.C;

         }

@@ -5912,6 +6287,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -5967,11 +6343,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetC(value); }

       }

       public Builder SetC(int value) {

+        PrepareBuilder();

         result.hasC = true;

         result.c_ = value;

         return this;

       }

       public Builder ClearC() {

+        PrepareBuilder();

         result.hasC = false;

         result.c_ = 0;

         return this;

@@ -6073,7 +6451,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestAllExtensions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -6083,21 +6461,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestAllExtensions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestAllExtensions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestAllExtensions result = new TestAllExtensions();

+      bool builderIsReadOnly;

+      TestAllExtensions result;

+      

+      private TestAllExtensions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestAllExtensions original = result;

+          result = new TestAllExtensions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestAllExtensions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestAllExtensions();

+        result = DefaultInstance ?? new TestAllExtensions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -6109,12 +6514,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestAllExtensions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestAllExtensions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -6128,6 +6532,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestAllExtensions other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestAllExtensions.DefaultInstance) return this;

+        PrepareBuilder();

           this.MergeExtensionFields(other);

         this.MergeUnknownFields(other.UnknownFields);

         return this;

@@ -6138,6 +6543,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -6289,7 +6695,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(OptionalGroup_extension prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -6299,21 +6705,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new OptionalGroup_extension();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(OptionalGroup_extension cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      OptionalGroup_extension result = new OptionalGroup_extension();

+      bool builderIsReadOnly;

+      OptionalGroup_extension result;

+      

+      private OptionalGroup_extension PrepareBuilder() {

+        if (builderIsReadOnly) {

+          OptionalGroup_extension original = result;

+          result = new OptionalGroup_extension();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override OptionalGroup_extension MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new OptionalGroup_extension();

+        result = DefaultInstance ?? new OptionalGroup_extension();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -6325,12 +6758,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override OptionalGroup_extension BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        OptionalGroup_extension returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -6344,6 +6776,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(OptionalGroup_extension other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.OptionalGroup_extension.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           A = other.A;

         }

@@ -6356,6 +6789,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -6411,11 +6845,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetA(value); }

       }

       public Builder SetA(int value) {

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = 0;

         return this;

@@ -6529,7 +6965,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(RepeatedGroup_extension prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -6539,21 +6975,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new RepeatedGroup_extension();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(RepeatedGroup_extension cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      RepeatedGroup_extension result;

+      

+      private RepeatedGroup_extension PrepareBuilder() {

+        if (builderIsReadOnly) {

+          RepeatedGroup_extension original = result;

+          result = new RepeatedGroup_extension();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      RepeatedGroup_extension result = new RepeatedGroup_extension();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override RepeatedGroup_extension MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new RepeatedGroup_extension();

+        result = DefaultInstance ?? new RepeatedGroup_extension();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -6565,12 +7028,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override RepeatedGroup_extension BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        RepeatedGroup_extension returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -6584,6 +7046,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(RepeatedGroup_extension other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.RepeatedGroup_extension.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           A = other.A;

         }

@@ -6596,6 +7059,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -6651,11 +7115,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetA(value); }

       }

       public Builder SetA(int value) {

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = 0;

         return this;

@@ -6755,7 +7221,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestNestedExtension prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -6765,21 +7231,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestNestedExtension();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestNestedExtension cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestNestedExtension result;

+      

+      private TestNestedExtension PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestNestedExtension original = result;

+          result = new TestNestedExtension();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestNestedExtension result = new TestNestedExtension();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestNestedExtension MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestNestedExtension();

+        result = DefaultInstance ?? new TestNestedExtension();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -6791,12 +7284,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestNestedExtension BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestNestedExtension returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -6810,6 +7302,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestNestedExtension other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestNestedExtension.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -6819,6 +7312,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -7489,7 +7983,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestRequired prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -7499,21 +7993,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestRequired();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestRequired cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestRequired result = new TestRequired();

+      bool builderIsReadOnly;

+      TestRequired result;

+      

+      private TestRequired PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestRequired original = result;

+          result = new TestRequired();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestRequired MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestRequired();

+        result = DefaultInstance ?? new TestRequired();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -7525,12 +8046,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestRequired BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestRequired returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -7544,6 +8064,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestRequired other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestRequired.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           A = other.A;

         }

@@ -7652,6 +8173,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -7835,11 +8357,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetA(value); }

       }

       public Builder SetA(int value) {

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = 0;

         return this;

@@ -7853,11 +8377,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy2(value); }

       }

       public Builder SetDummy2(int value) {

+        PrepareBuilder();

         result.hasDummy2 = true;

         result.dummy2_ = value;

         return this;

       }

       public Builder ClearDummy2() {

+        PrepareBuilder();

         result.hasDummy2 = false;

         result.dummy2_ = 0;

         return this;

@@ -7871,11 +8397,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetB(value); }

       }

       public Builder SetB(int value) {

+        PrepareBuilder();

         result.hasB = true;

         result.b_ = value;

         return this;

       }

       public Builder ClearB() {

+        PrepareBuilder();

         result.hasB = false;

         result.b_ = 0;

         return this;

@@ -7889,11 +8417,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy4(value); }

       }

       public Builder SetDummy4(int value) {

+        PrepareBuilder();

         result.hasDummy4 = true;

         result.dummy4_ = value;

         return this;

       }

       public Builder ClearDummy4() {

+        PrepareBuilder();

         result.hasDummy4 = false;

         result.dummy4_ = 0;

         return this;

@@ -7907,11 +8437,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy5(value); }

       }

       public Builder SetDummy5(int value) {

+        PrepareBuilder();

         result.hasDummy5 = true;

         result.dummy5_ = value;

         return this;

       }

       public Builder ClearDummy5() {

+        PrepareBuilder();

         result.hasDummy5 = false;

         result.dummy5_ = 0;

         return this;

@@ -7925,11 +8457,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy6(value); }

       }

       public Builder SetDummy6(int value) {

+        PrepareBuilder();

         result.hasDummy6 = true;

         result.dummy6_ = value;

         return this;

       }

       public Builder ClearDummy6() {

+        PrepareBuilder();

         result.hasDummy6 = false;

         result.dummy6_ = 0;

         return this;

@@ -7943,11 +8477,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy7(value); }

       }

       public Builder SetDummy7(int value) {

+        PrepareBuilder();

         result.hasDummy7 = true;

         result.dummy7_ = value;

         return this;

       }

       public Builder ClearDummy7() {

+        PrepareBuilder();

         result.hasDummy7 = false;

         result.dummy7_ = 0;

         return this;

@@ -7961,11 +8497,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy8(value); }

       }

       public Builder SetDummy8(int value) {

+        PrepareBuilder();

         result.hasDummy8 = true;

         result.dummy8_ = value;

         return this;

       }

       public Builder ClearDummy8() {

+        PrepareBuilder();

         result.hasDummy8 = false;

         result.dummy8_ = 0;

         return this;

@@ -7979,11 +8517,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy9(value); }

       }

       public Builder SetDummy9(int value) {

+        PrepareBuilder();

         result.hasDummy9 = true;

         result.dummy9_ = value;

         return this;

       }

       public Builder ClearDummy9() {

+        PrepareBuilder();

         result.hasDummy9 = false;

         result.dummy9_ = 0;

         return this;

@@ -7997,11 +8537,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy10(value); }

       }

       public Builder SetDummy10(int value) {

+        PrepareBuilder();

         result.hasDummy10 = true;

         result.dummy10_ = value;

         return this;

       }

       public Builder ClearDummy10() {

+        PrepareBuilder();

         result.hasDummy10 = false;

         result.dummy10_ = 0;

         return this;

@@ -8015,11 +8557,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy11(value); }

       }

       public Builder SetDummy11(int value) {

+        PrepareBuilder();

         result.hasDummy11 = true;

         result.dummy11_ = value;

         return this;

       }

       public Builder ClearDummy11() {

+        PrepareBuilder();

         result.hasDummy11 = false;

         result.dummy11_ = 0;

         return this;

@@ -8033,11 +8577,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy12(value); }

       }

       public Builder SetDummy12(int value) {

+        PrepareBuilder();

         result.hasDummy12 = true;

         result.dummy12_ = value;

         return this;

       }

       public Builder ClearDummy12() {

+        PrepareBuilder();

         result.hasDummy12 = false;

         result.dummy12_ = 0;

         return this;

@@ -8051,11 +8597,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy13(value); }

       }

       public Builder SetDummy13(int value) {

+        PrepareBuilder();

         result.hasDummy13 = true;

         result.dummy13_ = value;

         return this;

       }

       public Builder ClearDummy13() {

+        PrepareBuilder();

         result.hasDummy13 = false;

         result.dummy13_ = 0;

         return this;

@@ -8069,11 +8617,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy14(value); }

       }

       public Builder SetDummy14(int value) {

+        PrepareBuilder();

         result.hasDummy14 = true;

         result.dummy14_ = value;

         return this;

       }

       public Builder ClearDummy14() {

+        PrepareBuilder();

         result.hasDummy14 = false;

         result.dummy14_ = 0;

         return this;

@@ -8087,11 +8637,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy15(value); }

       }

       public Builder SetDummy15(int value) {

+        PrepareBuilder();

         result.hasDummy15 = true;

         result.dummy15_ = value;

         return this;

       }

       public Builder ClearDummy15() {

+        PrepareBuilder();

         result.hasDummy15 = false;

         result.dummy15_ = 0;

         return this;

@@ -8105,11 +8657,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy16(value); }

       }

       public Builder SetDummy16(int value) {

+        PrepareBuilder();

         result.hasDummy16 = true;

         result.dummy16_ = value;

         return this;

       }

       public Builder ClearDummy16() {

+        PrepareBuilder();

         result.hasDummy16 = false;

         result.dummy16_ = 0;

         return this;

@@ -8123,11 +8677,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy17(value); }

       }

       public Builder SetDummy17(int value) {

+        PrepareBuilder();

         result.hasDummy17 = true;

         result.dummy17_ = value;

         return this;

       }

       public Builder ClearDummy17() {

+        PrepareBuilder();

         result.hasDummy17 = false;

         result.dummy17_ = 0;

         return this;

@@ -8141,11 +8697,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy18(value); }

       }

       public Builder SetDummy18(int value) {

+        PrepareBuilder();

         result.hasDummy18 = true;

         result.dummy18_ = value;

         return this;

       }

       public Builder ClearDummy18() {

+        PrepareBuilder();

         result.hasDummy18 = false;

         result.dummy18_ = 0;

         return this;

@@ -8159,11 +8717,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy19(value); }

       }

       public Builder SetDummy19(int value) {

+        PrepareBuilder();

         result.hasDummy19 = true;

         result.dummy19_ = value;

         return this;

       }

       public Builder ClearDummy19() {

+        PrepareBuilder();

         result.hasDummy19 = false;

         result.dummy19_ = 0;

         return this;

@@ -8177,11 +8737,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy20(value); }

       }

       public Builder SetDummy20(int value) {

+        PrepareBuilder();

         result.hasDummy20 = true;

         result.dummy20_ = value;

         return this;

       }

       public Builder ClearDummy20() {

+        PrepareBuilder();

         result.hasDummy20 = false;

         result.dummy20_ = 0;

         return this;

@@ -8195,11 +8757,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy21(value); }

       }

       public Builder SetDummy21(int value) {

+        PrepareBuilder();

         result.hasDummy21 = true;

         result.dummy21_ = value;

         return this;

       }

       public Builder ClearDummy21() {

+        PrepareBuilder();

         result.hasDummy21 = false;

         result.dummy21_ = 0;

         return this;

@@ -8213,11 +8777,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy22(value); }

       }

       public Builder SetDummy22(int value) {

+        PrepareBuilder();

         result.hasDummy22 = true;

         result.dummy22_ = value;

         return this;

       }

       public Builder ClearDummy22() {

+        PrepareBuilder();

         result.hasDummy22 = false;

         result.dummy22_ = 0;

         return this;

@@ -8231,11 +8797,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy23(value); }

       }

       public Builder SetDummy23(int value) {

+        PrepareBuilder();

         result.hasDummy23 = true;

         result.dummy23_ = value;

         return this;

       }

       public Builder ClearDummy23() {

+        PrepareBuilder();

         result.hasDummy23 = false;

         result.dummy23_ = 0;

         return this;

@@ -8249,11 +8817,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy24(value); }

       }

       public Builder SetDummy24(int value) {

+        PrepareBuilder();

         result.hasDummy24 = true;

         result.dummy24_ = value;

         return this;

       }

       public Builder ClearDummy24() {

+        PrepareBuilder();

         result.hasDummy24 = false;

         result.dummy24_ = 0;

         return this;

@@ -8267,11 +8837,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy25(value); }

       }

       public Builder SetDummy25(int value) {

+        PrepareBuilder();

         result.hasDummy25 = true;

         result.dummy25_ = value;

         return this;

       }

       public Builder ClearDummy25() {

+        PrepareBuilder();

         result.hasDummy25 = false;

         result.dummy25_ = 0;

         return this;

@@ -8285,11 +8857,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy26(value); }

       }

       public Builder SetDummy26(int value) {

+        PrepareBuilder();

         result.hasDummy26 = true;

         result.dummy26_ = value;

         return this;

       }

       public Builder ClearDummy26() {

+        PrepareBuilder();

         result.hasDummy26 = false;

         result.dummy26_ = 0;

         return this;

@@ -8303,11 +8877,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy27(value); }

       }

       public Builder SetDummy27(int value) {

+        PrepareBuilder();

         result.hasDummy27 = true;

         result.dummy27_ = value;

         return this;

       }

       public Builder ClearDummy27() {

+        PrepareBuilder();

         result.hasDummy27 = false;

         result.dummy27_ = 0;

         return this;

@@ -8321,11 +8897,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy28(value); }

       }

       public Builder SetDummy28(int value) {

+        PrepareBuilder();

         result.hasDummy28 = true;

         result.dummy28_ = value;

         return this;

       }

       public Builder ClearDummy28() {

+        PrepareBuilder();

         result.hasDummy28 = false;

         result.dummy28_ = 0;

         return this;

@@ -8339,11 +8917,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy29(value); }

       }

       public Builder SetDummy29(int value) {

+        PrepareBuilder();

         result.hasDummy29 = true;

         result.dummy29_ = value;

         return this;

       }

       public Builder ClearDummy29() {

+        PrepareBuilder();

         result.hasDummy29 = false;

         result.dummy29_ = 0;

         return this;

@@ -8357,11 +8937,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy30(value); }

       }

       public Builder SetDummy30(int value) {

+        PrepareBuilder();

         result.hasDummy30 = true;

         result.dummy30_ = value;

         return this;

       }

       public Builder ClearDummy30() {

+        PrepareBuilder();

         result.hasDummy30 = false;

         result.dummy30_ = 0;

         return this;

@@ -8375,11 +8957,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy31(value); }

       }

       public Builder SetDummy31(int value) {

+        PrepareBuilder();

         result.hasDummy31 = true;

         result.dummy31_ = value;

         return this;

       }

       public Builder ClearDummy31() {

+        PrepareBuilder();

         result.hasDummy31 = false;

         result.dummy31_ = 0;

         return this;

@@ -8393,11 +8977,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy32(value); }

       }

       public Builder SetDummy32(int value) {

+        PrepareBuilder();

         result.hasDummy32 = true;

         result.dummy32_ = value;

         return this;

       }

       public Builder ClearDummy32() {

+        PrepareBuilder();

         result.hasDummy32 = false;

         result.dummy32_ = 0;

         return this;

@@ -8411,11 +8997,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetC(value); }

       }

       public Builder SetC(int value) {

+        PrepareBuilder();

         result.hasC = true;

         result.c_ = value;

         return this;

       }

       public Builder ClearC() {

+        PrepareBuilder();

         result.hasC = false;

         result.c_ = 0;

         return this;

@@ -8569,7 +9157,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestRequiredForeign prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -8579,21 +9167,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestRequiredForeign();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestRequiredForeign cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestRequiredForeign result;

       

-      TestRequiredForeign result = new TestRequiredForeign();

+      private TestRequiredForeign PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestRequiredForeign original = result;

+          result = new TestRequiredForeign();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestRequiredForeign MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestRequiredForeign();

+        result = DefaultInstance ?? new TestRequiredForeign();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -8605,13 +9220,12 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestRequiredForeign BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.repeatedMessage_.MakeReadOnly();

-        TestRequiredForeign returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -8625,6 +9239,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestRequiredForeign other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestRequiredForeign.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasOptionalMessage) {

           MergeOptionalMessage(other.OptionalMessage);

         }

@@ -8643,6 +9258,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -8712,18 +9328,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalMessage(global::Google.ProtocolBuffers.TestProtos.TestRequired value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalMessage = true;

         result.optionalMessage_ = value;

         return this;

       }

       public Builder SetOptionalMessage(global::Google.ProtocolBuffers.TestProtos.TestRequired.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalMessage = true;

         result.optionalMessage_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalMessage(global::Google.ProtocolBuffers.TestProtos.TestRequired value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalMessage &&

             result.optionalMessage_ != global::Google.ProtocolBuffers.TestProtos.TestRequired.DefaultInstance) {

             result.optionalMessage_ = global::Google.ProtocolBuffers.TestProtos.TestRequired.CreateBuilder(result.optionalMessage_).MergeFrom(value).BuildPartial();

@@ -8734,13 +9353,14 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalMessage() {

+        PrepareBuilder();

         result.hasOptionalMessage = false;

         result.optionalMessage_ = global::Google.ProtocolBuffers.TestProtos.TestRequired.DefaultInstance;

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.TestRequired> RepeatedMessageList {

-        get { return result.repeatedMessage_; }

+        get { return PrepareBuilder().repeatedMessage_; }

       }

       public int RepeatedMessageCount {

         get { return result.RepeatedMessageCount; }

@@ -8750,29 +9370,35 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedMessage(int index, global::Google.ProtocolBuffers.TestProtos.TestRequired value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedMessage_[index] = value;

         return this;

       }

       public Builder SetRepeatedMessage(int index, global::Google.ProtocolBuffers.TestProtos.TestRequired.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedMessage_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedMessage(global::Google.ProtocolBuffers.TestProtos.TestRequired value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedMessage_.Add(value);

         return this;

       }

       public Builder AddRepeatedMessage(global::Google.ProtocolBuffers.TestProtos.TestRequired.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedMessage_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestRequired> values) {

+        PrepareBuilder();

         result.repeatedMessage_.Add(values);

         return this;

       }

       public Builder ClearRepeatedMessage() {

+        PrepareBuilder();

         result.repeatedMessage_.Clear();

         return this;

       }

@@ -8785,11 +9411,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDummy(value); }

       }

       public Builder SetDummy(int value) {

+        PrepareBuilder();

         result.hasDummy = true;

         result.dummy_ = value;

         return this;

       }

       public Builder ClearDummy() {

+        PrepareBuilder();

         result.hasDummy = false;

         result.dummy_ = 0;

         return this;

@@ -8903,7 +9531,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestForeignNested prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -8913,21 +9541,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestForeignNested();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestForeignNested cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestForeignNested result = new TestForeignNested();

+      bool builderIsReadOnly;

+      TestForeignNested result;

+      

+      private TestForeignNested PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestForeignNested original = result;

+          result = new TestForeignNested();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestForeignNested MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestForeignNested();

+        result = DefaultInstance ?? new TestForeignNested();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -8939,12 +9594,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestForeignNested BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestForeignNested returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -8958,6 +9612,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestForeignNested other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestForeignNested.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasForeignNested) {

           MergeForeignNested(other.ForeignNested);

         }

@@ -8970,6 +9625,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -9031,18 +9687,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetForeignNested(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasForeignNested = true;

         result.foreignNested_ = value;

         return this;

       }

       public Builder SetForeignNested(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasForeignNested = true;

         result.foreignNested_ = builderForValue.Build();

         return this;

       }

       public Builder MergeForeignNested(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasForeignNested &&

             result.foreignNested_ != global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance) {

             result.foreignNested_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.CreateBuilder(result.foreignNested_).MergeFrom(value).BuildPartial();

@@ -9053,6 +9712,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearForeignNested() {

+        PrepareBuilder();

         result.hasForeignNested = false;

         result.foreignNested_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance;

         return this;

@@ -9150,7 +9810,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestEmptyMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -9160,21 +9820,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestEmptyMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestEmptyMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestEmptyMessage result;

+      

+      private TestEmptyMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestEmptyMessage original = result;

+          result = new TestEmptyMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestEmptyMessage result = new TestEmptyMessage();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestEmptyMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestEmptyMessage();

+        result = DefaultInstance ?? new TestEmptyMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -9186,12 +9873,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestEmptyMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestEmptyMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -9205,6 +9891,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestEmptyMessage other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestEmptyMessage.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -9214,6 +9901,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -9353,7 +10041,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestEmptyMessageWithExtensions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -9363,21 +10051,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestEmptyMessageWithExtensions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestEmptyMessageWithExtensions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestEmptyMessageWithExtensions result = new TestEmptyMessageWithExtensions();

+      bool builderIsReadOnly;

+      TestEmptyMessageWithExtensions result;

+      

+      private TestEmptyMessageWithExtensions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestEmptyMessageWithExtensions original = result;

+          result = new TestEmptyMessageWithExtensions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestEmptyMessageWithExtensions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestEmptyMessageWithExtensions();

+        result = DefaultInstance ?? new TestEmptyMessageWithExtensions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -9389,12 +10104,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestEmptyMessageWithExtensions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestEmptyMessageWithExtensions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -9408,6 +10122,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestEmptyMessageWithExtensions other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestEmptyMessageWithExtensions.DefaultInstance) return this;

+        PrepareBuilder();

           this.MergeExtensionFields(other);

         this.MergeUnknownFields(other.UnknownFields);

         return this;

@@ -9418,6 +10133,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -9559,7 +10275,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestMultipleExtensionRanges prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -9569,21 +10285,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestMultipleExtensionRanges();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestMultipleExtensionRanges cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestMultipleExtensionRanges result;

+      

+      private TestMultipleExtensionRanges PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestMultipleExtensionRanges original = result;

+          result = new TestMultipleExtensionRanges();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestMultipleExtensionRanges result = new TestMultipleExtensionRanges();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestMultipleExtensionRanges MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestMultipleExtensionRanges();

+        result = DefaultInstance ?? new TestMultipleExtensionRanges();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -9595,12 +10338,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestMultipleExtensionRanges BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestMultipleExtensionRanges returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -9614,6 +10356,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestMultipleExtensionRanges other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestMultipleExtensionRanges.DefaultInstance) return this;

+        PrepareBuilder();

           this.MergeExtensionFields(other);

         this.MergeUnknownFields(other.UnknownFields);

         return this;

@@ -9624,6 +10367,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -9791,7 +10535,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestReallyLargeTagNumber prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -9801,21 +10545,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestReallyLargeTagNumber();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestReallyLargeTagNumber cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestReallyLargeTagNumber result;

+      

+      private TestReallyLargeTagNumber PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestReallyLargeTagNumber original = result;

+          result = new TestReallyLargeTagNumber();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestReallyLargeTagNumber result = new TestReallyLargeTagNumber();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestReallyLargeTagNumber MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestReallyLargeTagNumber();

+        result = DefaultInstance ?? new TestReallyLargeTagNumber();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -9827,12 +10598,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestReallyLargeTagNumber BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestReallyLargeTagNumber returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -9846,6 +10616,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestReallyLargeTagNumber other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestReallyLargeTagNumber.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           A = other.A;

         }

@@ -9861,6 +10632,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -9920,11 +10692,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetA(value); }

       }

       public Builder SetA(int value) {

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = 0;

         return this;

@@ -9938,11 +10712,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetBb(value); }

       }

       public Builder SetBb(int value) {

+        PrepareBuilder();

         result.hasBb = true;

         result.bb_ = value;

         return this;

       }

       public Builder ClearBb() {

+        PrepareBuilder();

         result.hasBb = false;

         result.bb_ = 0;

         return this;

@@ -10072,7 +10848,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestRecursiveMessage prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -10082,21 +10858,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestRecursiveMessage();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestRecursiveMessage cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestRecursiveMessage result = new TestRecursiveMessage();

+      bool builderIsReadOnly;

+      TestRecursiveMessage result;

+      

+      private TestRecursiveMessage PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestRecursiveMessage original = result;

+          result = new TestRecursiveMessage();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestRecursiveMessage MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestRecursiveMessage();

+        result = DefaultInstance ?? new TestRecursiveMessage();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -10108,12 +10911,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestRecursiveMessage BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestRecursiveMessage returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -10127,6 +10929,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestRecursiveMessage other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           MergeA(other.A);

         }

@@ -10142,6 +10945,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -10207,18 +11011,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetA(global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder SetA(global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = builderForValue.Build();

         return this;

       }

       public Builder MergeA(global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasA &&

             result.a_ != global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage.DefaultInstance) {

             result.a_ = global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage.CreateBuilder(result.a_).MergeFrom(value).BuildPartial();

@@ -10229,6 +11036,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage.DefaultInstance;

         return this;

@@ -10242,11 +11050,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetI(value); }

       }

       public Builder SetI(int value) {

+        PrepareBuilder();

         result.hasI = true;

         result.i_ = value;

         return this;

       }

       public Builder ClearI() {

+        PrepareBuilder();

         result.hasI = false;

         result.i_ = 0;

         return this;

@@ -10360,7 +11170,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestMutualRecursionA prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -10370,21 +11180,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestMutualRecursionA();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestMutualRecursionA cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestMutualRecursionA result;

+      

+      private TestMutualRecursionA PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestMutualRecursionA original = result;

+          result = new TestMutualRecursionA();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestMutualRecursionA result = new TestMutualRecursionA();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestMutualRecursionA MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestMutualRecursionA();

+        result = DefaultInstance ?? new TestMutualRecursionA();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -10396,12 +11233,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestMutualRecursionA BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestMutualRecursionA returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -10415,6 +11251,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestMutualRecursionA other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasBb) {

           MergeBb(other.Bb);

         }

@@ -10427,6 +11264,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -10488,18 +11326,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetBb(global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasBb = true;

         result.bb_ = value;

         return this;

       }

       public Builder SetBb(global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasBb = true;

         result.bb_ = builderForValue.Build();

         return this;

       }

       public Builder MergeBb(global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasBb &&

             result.bb_ != global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB.DefaultInstance) {

             result.bb_ = global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB.CreateBuilder(result.bb_).MergeFrom(value).BuildPartial();

@@ -10510,6 +11351,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearBb() {

+        PrepareBuilder();

         result.hasBb = false;

         result.bb_ = global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB.DefaultInstance;

         return this;

@@ -10639,7 +11481,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestMutualRecursionB prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -10649,21 +11491,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestMutualRecursionB();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestMutualRecursionB cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestMutualRecursionB result = new TestMutualRecursionB();

+      bool builderIsReadOnly;

+      TestMutualRecursionB result;

+      

+      private TestMutualRecursionB PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestMutualRecursionB original = result;

+          result = new TestMutualRecursionB();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestMutualRecursionB MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestMutualRecursionB();

+        result = DefaultInstance ?? new TestMutualRecursionB();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -10675,12 +11544,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestMutualRecursionB BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestMutualRecursionB returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -10694,6 +11562,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestMutualRecursionB other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           MergeA(other.A);

         }

@@ -10709,6 +11578,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -10774,18 +11644,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetA(global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder SetA(global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = builderForValue.Build();

         return this;

       }

       public Builder MergeA(global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasA &&

             result.a_ != global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA.DefaultInstance) {

             result.a_ = global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA.CreateBuilder(result.a_).MergeFrom(value).BuildPartial();

@@ -10796,6 +11669,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA.DefaultInstance;

         return this;

@@ -10809,11 +11683,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOptionalInt32(value); }

       }

       public Builder SetOptionalInt32(int value) {

+        PrepareBuilder();

         result.hasOptionalInt32 = true;

         result.optionalInt32_ = value;

         return this;

       }

       public Builder ClearOptionalInt32() {

+        PrepareBuilder();

         result.hasOptionalInt32 = false;

         result.optionalInt32_ = 0;

         return this;

@@ -10960,7 +11836,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(Foo prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -10970,21 +11846,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new Foo();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(Foo cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          Foo result;

           

-          Foo result = new Foo();

+          private Foo PrepareBuilder() {

+            if (builderIsReadOnly) {

+              Foo original = result;

+              result = new Foo();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override Foo MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new Foo();

+            result = DefaultInstance ?? new Foo();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -10996,12 +11899,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Foo BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            Foo returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -11015,6 +11917,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(Foo other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasA) {

               A = other.A;

             }

@@ -11027,6 +11930,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -11082,11 +11986,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetA(value); }

           }

           public Builder SetA(int value) {

+            PrepareBuilder();

             result.hasA = true;

             result.a_ = value;

             return this;

           }

           public Builder ClearA() {

+            PrepareBuilder();

             result.hasA = false;

             result.a_ = 0;

             return this;

@@ -11200,7 +12106,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(Bar prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -11210,21 +12116,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new Bar();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(Bar cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

           

-          Bar result = new Bar();

+          bool builderIsReadOnly;

+          Bar result;

+          

+          private Bar PrepareBuilder() {

+            if (builderIsReadOnly) {

+              Bar original = result;

+              result = new Bar();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override Bar MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new Bar();

+            result = DefaultInstance ?? new Bar();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -11236,12 +12169,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Bar BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            Bar returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -11255,6 +12187,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(Bar other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasA) {

               A = other.A;

             }

@@ -11267,6 +12200,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -11322,11 +12256,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetA(value); }

           }

           public Builder SetA(int value) {

+            PrepareBuilder();

             result.hasA = true;

             result.a_ = value;

             return this;

           }

           public Builder ClearA() {

+            PrepareBuilder();

             result.hasA = false;

             result.a_ = 0;

             return this;

@@ -11447,7 +12383,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestDupFieldNumber prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -11457,21 +12393,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestDupFieldNumber();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestDupFieldNumber cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestDupFieldNumber result = new TestDupFieldNumber();

+      bool builderIsReadOnly;

+      TestDupFieldNumber result;

+      

+      private TestDupFieldNumber PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestDupFieldNumber original = result;

+          result = new TestDupFieldNumber();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestDupFieldNumber MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestDupFieldNumber();

+        result = DefaultInstance ?? new TestDupFieldNumber();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -11483,12 +12446,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestDupFieldNumber BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestDupFieldNumber returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -11502,6 +12464,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestDupFieldNumber other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasA) {

           A = other.A;

         }

@@ -11520,6 +12483,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -11593,11 +12557,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetA(value); }

       }

       public Builder SetA(int value) {

+        PrepareBuilder();

         result.hasA = true;

         result.a_ = value;

         return this;

       }

       public Builder ClearA() {

+        PrepareBuilder();

         result.hasA = false;

         result.a_ = 0;

         return this;

@@ -11612,18 +12578,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetFoo(global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasFoo = true;

         result.foo_ = value;

         return this;

       }

       public Builder SetFoo(global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasFoo = true;

         result.foo_ = builderForValue.Build();

         return this;

       }

       public Builder MergeFoo(global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasFoo &&

             result.foo_ != global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo.DefaultInstance) {

             result.foo_ = global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo.CreateBuilder(result.foo_).MergeFrom(value).BuildPartial();

@@ -11634,6 +12603,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearFoo() {

+        PrepareBuilder();

         result.hasFoo = false;

         result.foo_ = global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo.DefaultInstance;

         return this;

@@ -11648,18 +12618,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetBar(global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasBar = true;

         result.bar_ = value;

         return this;

       }

       public Builder SetBar(global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasBar = true;

         result.bar_ = builderForValue.Build();

         return this;

       }

       public Builder MergeBar(global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasBar &&

             result.bar_ != global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar.DefaultInstance) {

             result.bar_ = global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar.CreateBuilder(result.bar_).MergeFrom(value).BuildPartial();

@@ -11670,6 +12643,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearBar() {

+        PrepareBuilder();

         result.hasBar = false;

         result.bar_ = global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar.DefaultInstance;

         return this;

@@ -11841,7 +12815,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(NestedMessage prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -11851,21 +12825,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new NestedMessage();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(NestedMessage cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          NestedMessage result;

+          

+          private NestedMessage PrepareBuilder() {

+            if (builderIsReadOnly) {

+              NestedMessage original = result;

+              result = new NestedMessage();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

           

-          NestedMessage result = new NestedMessage();

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override NestedMessage MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new NestedMessage();

+            result = DefaultInstance ?? new NestedMessage();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -11877,14 +12878,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override NestedMessage BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

             result.nestedmessageRepeatedInt32_.MakeReadOnly();

             result.nestedmessageRepeatedForeignmessage_.MakeReadOnly();

-            NestedMessage returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -11898,6 +12898,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(NestedMessage other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.nestedmessageRepeatedInt32_.Count != 0) {

               result.nestedmessageRepeatedInt32_.Add(other.nestedmessageRepeatedInt32_);

             }

@@ -11913,6 +12914,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -11966,7 +12968,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           

           public pbc::IPopsicleList<int> NestedmessageRepeatedInt32List {

-            get { return result.nestedmessageRepeatedInt32_; }

+            get { return PrepareBuilder().nestedmessageRepeatedInt32_; }

           }

           public int NestedmessageRepeatedInt32Count {

             get { return result.NestedmessageRepeatedInt32Count; }

@@ -11975,24 +12977,28 @@ namespace Google.ProtocolBuffers.TestProtos {
             return result.GetNestedmessageRepeatedInt32(index);

           }

           public Builder SetNestedmessageRepeatedInt32(int index, int value) {

+            PrepareBuilder();

             result.nestedmessageRepeatedInt32_[index] = value;

             return this;

           }

           public Builder AddNestedmessageRepeatedInt32(int value) {

+            PrepareBuilder();

             result.nestedmessageRepeatedInt32_.Add(value);

             return this;

           }

           public Builder AddRangeNestedmessageRepeatedInt32(scg::IEnumerable<int> values) {

+            PrepareBuilder();

             result.nestedmessageRepeatedInt32_.Add(values);

             return this;

           }

           public Builder ClearNestedmessageRepeatedInt32() {

+            PrepareBuilder();

             result.nestedmessageRepeatedInt32_.Clear();

             return this;

           }

           

           public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> NestedmessageRepeatedForeignmessageList {

-            get { return result.nestedmessageRepeatedForeignmessage_; }

+            get { return PrepareBuilder().nestedmessageRepeatedForeignmessage_; }

           }

           public int NestedmessageRepeatedForeignmessageCount {

             get { return result.NestedmessageRepeatedForeignmessageCount; }

@@ -12002,29 +13008,35 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           public Builder SetNestedmessageRepeatedForeignmessage(int index, global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.nestedmessageRepeatedForeignmessage_[index] = value;

             return this;

           }

           public Builder SetNestedmessageRepeatedForeignmessage(int index, global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

             pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+            PrepareBuilder();

             result.nestedmessageRepeatedForeignmessage_[index] = builderForValue.Build();

             return this;

           }

           public Builder AddNestedmessageRepeatedForeignmessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

             pb::ThrowHelper.ThrowIfNull(value, "value");

+            PrepareBuilder();

             result.nestedmessageRepeatedForeignmessage_.Add(value);

             return this;

           }

           public Builder AddNestedmessageRepeatedForeignmessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

             pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+            PrepareBuilder();

             result.nestedmessageRepeatedForeignmessage_.Add(builderForValue.Build());

             return this;

           }

           public Builder AddRangeNestedmessageRepeatedForeignmessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> values) {

+            PrepareBuilder();

             result.nestedmessageRepeatedForeignmessage_.Add(values);

             return this;

           }

           public Builder ClearNestedmessageRepeatedForeignmessage() {

+            PrepareBuilder();

             result.nestedmessageRepeatedForeignmessage_.Clear();

             return this;

           }

@@ -12112,7 +13124,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestNestedMessageHasBits prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -12122,21 +13134,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestNestedMessageHasBits();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestNestedMessageHasBits cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestNestedMessageHasBits result = new TestNestedMessageHasBits();

+      bool builderIsReadOnly;

+      TestNestedMessageHasBits result;

+      

+      private TestNestedMessageHasBits PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestNestedMessageHasBits original = result;

+          result = new TestNestedMessageHasBits();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestNestedMessageHasBits MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestNestedMessageHasBits();

+        result = DefaultInstance ?? new TestNestedMessageHasBits();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -12148,12 +13187,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestNestedMessageHasBits BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestNestedMessageHasBits returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -12167,6 +13205,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestNestedMessageHasBits other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasOptionalNestedMessage) {

           MergeOptionalNestedMessage(other.OptionalNestedMessage);

         }

@@ -12179,6 +13218,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -12240,18 +13280,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasOptionalNestedMessage = true;

         result.optionalNestedMessage_ = value;

         return this;

       }

       public Builder SetOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasOptionalNestedMessage = true;

         result.optionalNestedMessage_ = builderForValue.Build();

         return this;

       }

       public Builder MergeOptionalNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasOptionalNestedMessage &&

             result.optionalNestedMessage_ != global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage.DefaultInstance) {

             result.optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage.CreateBuilder(result.optionalNestedMessage_).MergeFrom(value).BuildPartial();

@@ -12262,6 +13305,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearOptionalNestedMessage() {

+        PrepareBuilder();

         result.hasOptionalNestedMessage = false;

         result.optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage.DefaultInstance;

         return this;

@@ -12590,7 +13634,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestCamelCaseFieldNames prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -12600,21 +13644,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestCamelCaseFieldNames();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestCamelCaseFieldNames cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestCamelCaseFieldNames result;

+      

+      private TestCamelCaseFieldNames PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestCamelCaseFieldNames original = result;

+          result = new TestCamelCaseFieldNames();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestCamelCaseFieldNames result = new TestCamelCaseFieldNames();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestCamelCaseFieldNames MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestCamelCaseFieldNames();

+        result = DefaultInstance ?? new TestCamelCaseFieldNames();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -12626,8 +13697,8 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestCamelCaseFieldNames BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.repeatedPrimitiveField_.MakeReadOnly();

         result.repeatedStringField_.MakeReadOnly();

@@ -12635,9 +13706,8 @@ namespace Google.ProtocolBuffers.TestProtos {
         result.repeatedMessageField_.MakeReadOnly();

         result.repeatedStringPieceField_.MakeReadOnly();

         result.repeatedCordField_.MakeReadOnly();

-        TestCamelCaseFieldNames returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -12651,6 +13721,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestCamelCaseFieldNames other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestCamelCaseFieldNames.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasPrimitiveField) {

           PrimitiveField = other.PrimitiveField;

         }

@@ -12696,6 +13767,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -12819,11 +13891,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetPrimitiveField(value); }

       }

       public Builder SetPrimitiveField(int value) {

+        PrepareBuilder();

         result.hasPrimitiveField = true;

         result.primitiveField_ = value;

         return this;

       }

       public Builder ClearPrimitiveField() {

+        PrepareBuilder();

         result.hasPrimitiveField = false;

         result.primitiveField_ = 0;

         return this;

@@ -12838,11 +13912,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetStringField(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasStringField = true;

         result.stringField_ = value;

         return this;

       }

       public Builder ClearStringField() {

+        PrepareBuilder();

         result.hasStringField = false;

         result.stringField_ = "";

         return this;

@@ -12856,11 +13932,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetEnumField(value); }

       }

       public Builder SetEnumField(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.hasEnumField = true;

         result.enumField_ = value;

         return this;

       }

       public Builder ClearEnumField() {

+        PrepareBuilder();

         result.hasEnumField = false;

         result.enumField_ = global::Google.ProtocolBuffers.TestProtos.ForeignEnum.FOREIGN_FOO;

         return this;

@@ -12875,18 +13953,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetMessageField(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasMessageField = true;

         result.messageField_ = value;

         return this;

       }

       public Builder SetMessageField(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasMessageField = true;

         result.messageField_ = builderForValue.Build();

         return this;

       }

       public Builder MergeMessageField(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasMessageField &&

             result.messageField_ != global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance) {

             result.messageField_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.CreateBuilder(result.messageField_).MergeFrom(value).BuildPartial();

@@ -12897,6 +13978,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearMessageField() {

+        PrepareBuilder();

         result.hasMessageField = false;

         result.messageField_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance;

         return this;

@@ -12911,11 +13993,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetStringPieceField(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasStringPieceField = true;

         result.stringPieceField_ = value;

         return this;

       }

       public Builder ClearStringPieceField() {

+        PrepareBuilder();

         result.hasStringPieceField = false;

         result.stringPieceField_ = "";

         return this;

@@ -12930,18 +14014,20 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetCordField(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasCordField = true;

         result.cordField_ = value;

         return this;

       }

       public Builder ClearCordField() {

+        PrepareBuilder();

         result.hasCordField = false;

         result.cordField_ = "";

         return this;

       }

       

       public pbc::IPopsicleList<int> RepeatedPrimitiveFieldList {

-        get { return result.repeatedPrimitiveField_; }

+        get { return PrepareBuilder().repeatedPrimitiveField_; }

       }

       public int RepeatedPrimitiveFieldCount {

         get { return result.RepeatedPrimitiveFieldCount; }

@@ -12950,24 +14036,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedPrimitiveField(index);

       }

       public Builder SetRepeatedPrimitiveField(int index, int value) {

+        PrepareBuilder();

         result.repeatedPrimitiveField_[index] = value;

         return this;

       }

       public Builder AddRepeatedPrimitiveField(int value) {

+        PrepareBuilder();

         result.repeatedPrimitiveField_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedPrimitiveField(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.repeatedPrimitiveField_.Add(values);

         return this;

       }

       public Builder ClearRepeatedPrimitiveField() {

+        PrepareBuilder();

         result.repeatedPrimitiveField_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedStringFieldList {

-        get { return result.repeatedStringField_; }

+        get { return PrepareBuilder().repeatedStringField_; }

       }

       public int RepeatedStringFieldCount {

         get { return result.RepeatedStringFieldCount; }

@@ -12977,25 +14067,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedStringField(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedStringField_[index] = value;

         return this;

       }

       public Builder AddRepeatedStringField(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedStringField_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedStringField(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedStringField_.Add(values);

         return this;

       }

       public Builder ClearRepeatedStringField() {

+        PrepareBuilder();

         result.repeatedStringField_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> RepeatedEnumFieldList {

-        get { return result.repeatedEnumField_; }

+        get { return PrepareBuilder().repeatedEnumField_; }

       }

       public int RepeatedEnumFieldCount {

         get { return result.RepeatedEnumFieldCount; }

@@ -13004,24 +14098,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedEnumField(index);

       }

       public Builder SetRepeatedEnumField(int index, global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.repeatedEnumField_[index] = value;

         return this;

       }

       public Builder AddRepeatedEnumField(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.repeatedEnumField_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedEnumField(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> values) {

+        PrepareBuilder();

         result.repeatedEnumField_.Add(values);

         return this;

       }

       public Builder ClearRepeatedEnumField() {

+        PrepareBuilder();

         result.repeatedEnumField_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> RepeatedMessageFieldList {

-        get { return result.repeatedMessageField_; }

+        get { return PrepareBuilder().repeatedMessageField_; }

       }

       public int RepeatedMessageFieldCount {

         get { return result.RepeatedMessageFieldCount; }

@@ -13031,35 +14129,41 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedMessageField(int index, global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedMessageField_[index] = value;

         return this;

       }

       public Builder SetRepeatedMessageField(int index, global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedMessageField_[index] = builderForValue.Build();

         return this;

       }

       public Builder AddRepeatedMessageField(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedMessageField_.Add(value);

         return this;

       }

       public Builder AddRepeatedMessageField(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.repeatedMessageField_.Add(builderForValue.Build());

         return this;

       }

       public Builder AddRangeRepeatedMessageField(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> values) {

+        PrepareBuilder();

         result.repeatedMessageField_.Add(values);

         return this;

       }

       public Builder ClearRepeatedMessageField() {

+        PrepareBuilder();

         result.repeatedMessageField_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedStringPieceFieldList {

-        get { return result.repeatedStringPieceField_; }

+        get { return PrepareBuilder().repeatedStringPieceField_; }

       }

       public int RepeatedStringPieceFieldCount {

         get { return result.RepeatedStringPieceFieldCount; }

@@ -13069,25 +14173,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedStringPieceField(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedStringPieceField_[index] = value;

         return this;

       }

       public Builder AddRepeatedStringPieceField(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedStringPieceField_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedStringPieceField(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedStringPieceField_.Add(values);

         return this;

       }

       public Builder ClearRepeatedStringPieceField() {

+        PrepareBuilder();

         result.repeatedStringPieceField_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedCordFieldList {

-        get { return result.repeatedCordField_; }

+        get { return PrepareBuilder().repeatedCordField_; }

       }

       public int RepeatedCordFieldCount {

         get { return result.RepeatedCordFieldCount; }

@@ -13097,19 +14205,23 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedCordField(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedCordField_[index] = value;

         return this;

       }

       public Builder AddRepeatedCordField(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedCordField_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedCordField(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedCordField_.Add(values);

         return this;

       }

       public Builder ClearRepeatedCordField() {

+        PrepareBuilder();

         result.repeatedCordField_.Clear();

         return this;

       }

@@ -13259,7 +14371,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestFieldOrderings prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -13269,21 +14381,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestFieldOrderings();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestFieldOrderings cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestFieldOrderings result;

+      

+      private TestFieldOrderings PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestFieldOrderings original = result;

+          result = new TestFieldOrderings();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestFieldOrderings result = new TestFieldOrderings();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestFieldOrderings MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestFieldOrderings();

+        result = DefaultInstance ?? new TestFieldOrderings();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -13295,12 +14434,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestFieldOrderings BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestFieldOrderings returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -13314,6 +14452,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestFieldOrderings other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestFieldOrderings.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasMyString) {

           MyString = other.MyString;

         }

@@ -13333,6 +14472,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -13397,11 +14537,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetMyString(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasMyString = true;

         result.myString_ = value;

         return this;

       }

       public Builder ClearMyString() {

+        PrepareBuilder();

         result.hasMyString = false;

         result.myString_ = "";

         return this;

@@ -13415,11 +14557,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetMyInt(value); }

       }

       public Builder SetMyInt(long value) {

+        PrepareBuilder();

         result.hasMyInt = true;

         result.myInt_ = value;

         return this;

       }

       public Builder ClearMyInt() {

+        PrepareBuilder();

         result.hasMyInt = false;

         result.myInt_ = 0L;

         return this;

@@ -13433,11 +14577,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetMyFloat(value); }

       }

       public Builder SetMyFloat(float value) {

+        PrepareBuilder();

         result.hasMyFloat = true;

         result.myFloat_ = value;

         return this;

       }

       public Builder ClearMyFloat() {

+        PrepareBuilder();

         result.hasMyFloat = false;

         result.myFloat_ = 0F;

         return this;

@@ -13841,7 +14987,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestExtremeDefaultValues prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -13851,21 +14997,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestExtremeDefaultValues();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestExtremeDefaultValues cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestExtremeDefaultValues result;

       

-      TestExtremeDefaultValues result = new TestExtremeDefaultValues();

+      private TestExtremeDefaultValues PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestExtremeDefaultValues original = result;

+          result = new TestExtremeDefaultValues();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestExtremeDefaultValues MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestExtremeDefaultValues();

+        result = DefaultInstance ?? new TestExtremeDefaultValues();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -13877,12 +15050,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestExtremeDefaultValues BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestExtremeDefaultValues returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -13896,6 +15068,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestExtremeDefaultValues other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestExtremeDefaultValues.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasEscapedBytes) {

           EscapedBytes = other.EscapedBytes;

         }

@@ -13962,6 +15135,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -14090,11 +15264,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetEscapedBytes(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasEscapedBytes = true;

         result.escapedBytes_ = value;

         return this;

       }

       public Builder ClearEscapedBytes() {

+        PrepareBuilder();

         result.hasEscapedBytes = false;

         result.escapedBytes_ = (pb::ByteString) global::Google.ProtocolBuffers.TestProtos.TestExtremeDefaultValues.Descriptor.Fields[0].DefaultValue;

         return this;

@@ -14110,11 +15286,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetLargeUint32(uint value) {

+        PrepareBuilder();

         result.hasLargeUint32 = true;

         result.largeUint32_ = value;

         return this;

       }

       public Builder ClearLargeUint32() {

+        PrepareBuilder();

         result.hasLargeUint32 = false;

         result.largeUint32_ = 4294967295;

         return this;

@@ -14130,11 +15308,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetLargeUint64(ulong value) {

+        PrepareBuilder();

         result.hasLargeUint64 = true;

         result.largeUint64_ = value;

         return this;

       }

       public Builder ClearLargeUint64() {

+        PrepareBuilder();

         result.hasLargeUint64 = false;

         result.largeUint64_ = 18446744073709551615UL;

         return this;

@@ -14148,11 +15328,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetSmallInt32(value); }

       }

       public Builder SetSmallInt32(int value) {

+        PrepareBuilder();

         result.hasSmallInt32 = true;

         result.smallInt32_ = value;

         return this;

       }

       public Builder ClearSmallInt32() {

+        PrepareBuilder();

         result.hasSmallInt32 = false;

         result.smallInt32_ = -2147483647;

         return this;

@@ -14166,11 +15348,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetSmallInt64(value); }

       }

       public Builder SetSmallInt64(long value) {

+        PrepareBuilder();

         result.hasSmallInt64 = true;

         result.smallInt64_ = value;

         return this;

       }

       public Builder ClearSmallInt64() {

+        PrepareBuilder();

         result.hasSmallInt64 = false;

         result.smallInt64_ = -9223372036854775807L;

         return this;

@@ -14185,11 +15369,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetUtf8String(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasUtf8String = true;

         result.utf8String_ = value;

         return this;

       }

       public Builder ClearUtf8String() {

+        PrepareBuilder();

         result.hasUtf8String = false;

         result.utf8String_ = (string) global::Google.ProtocolBuffers.TestProtos.TestExtremeDefaultValues.Descriptor.Fields[5].DefaultValue;

         return this;

@@ -14203,11 +15389,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetZeroFloat(value); }

       }

       public Builder SetZeroFloat(float value) {

+        PrepareBuilder();

         result.hasZeroFloat = true;

         result.zeroFloat_ = value;

         return this;

       }

       public Builder ClearZeroFloat() {

+        PrepareBuilder();

         result.hasZeroFloat = false;

         result.zeroFloat_ = 0F;

         return this;

@@ -14221,11 +15409,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetOneFloat(value); }

       }

       public Builder SetOneFloat(float value) {

+        PrepareBuilder();

         result.hasOneFloat = true;

         result.oneFloat_ = value;

         return this;

       }

       public Builder ClearOneFloat() {

+        PrepareBuilder();

         result.hasOneFloat = false;

         result.oneFloat_ = 1F;

         return this;

@@ -14239,11 +15429,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetSmallFloat(value); }

       }

       public Builder SetSmallFloat(float value) {

+        PrepareBuilder();

         result.hasSmallFloat = true;

         result.smallFloat_ = value;

         return this;

       }

       public Builder ClearSmallFloat() {

+        PrepareBuilder();

         result.hasSmallFloat = false;

         result.smallFloat_ = 1.5F;

         return this;

@@ -14257,11 +15449,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetNegativeOneFloat(value); }

       }

       public Builder SetNegativeOneFloat(float value) {

+        PrepareBuilder();

         result.hasNegativeOneFloat = true;

         result.negativeOneFloat_ = value;

         return this;

       }

       public Builder ClearNegativeOneFloat() {

+        PrepareBuilder();

         result.hasNegativeOneFloat = false;

         result.negativeOneFloat_ = -1F;

         return this;

@@ -14275,11 +15469,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetNegativeFloat(value); }

       }

       public Builder SetNegativeFloat(float value) {

+        PrepareBuilder();

         result.hasNegativeFloat = true;

         result.negativeFloat_ = value;

         return this;

       }

       public Builder ClearNegativeFloat() {

+        PrepareBuilder();

         result.hasNegativeFloat = false;

         result.negativeFloat_ = -1.5F;

         return this;

@@ -14293,11 +15489,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetLargeFloat(value); }

       }

       public Builder SetLargeFloat(float value) {

+        PrepareBuilder();

         result.hasLargeFloat = true;

         result.largeFloat_ = value;

         return this;

       }

       public Builder ClearLargeFloat() {

+        PrepareBuilder();

         result.hasLargeFloat = false;

         result.largeFloat_ = 2E+08F;

         return this;

@@ -14311,11 +15509,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetSmallNegativeFloat(value); }

       }

       public Builder SetSmallNegativeFloat(float value) {

+        PrepareBuilder();

         result.hasSmallNegativeFloat = true;

         result.smallNegativeFloat_ = value;

         return this;

       }

       public Builder ClearSmallNegativeFloat() {

+        PrepareBuilder();

         result.hasSmallNegativeFloat = false;

         result.smallNegativeFloat_ = -8E-28F;

         return this;

@@ -14329,11 +15529,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetInfDouble(value); }

       }

       public Builder SetInfDouble(double value) {

+        PrepareBuilder();

         result.hasInfDouble = true;

         result.infDouble_ = value;

         return this;

       }

       public Builder ClearInfDouble() {

+        PrepareBuilder();

         result.hasInfDouble = false;

         result.infDouble_ = double.PositiveInfinity;

         return this;

@@ -14347,11 +15549,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetNegInfDouble(value); }

       }

       public Builder SetNegInfDouble(double value) {

+        PrepareBuilder();

         result.hasNegInfDouble = true;

         result.negInfDouble_ = value;

         return this;

       }

       public Builder ClearNegInfDouble() {

+        PrepareBuilder();

         result.hasNegInfDouble = false;

         result.negInfDouble_ = double.NegativeInfinity;

         return this;

@@ -14365,11 +15569,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetNanDouble(value); }

       }

       public Builder SetNanDouble(double value) {

+        PrepareBuilder();

         result.hasNanDouble = true;

         result.nanDouble_ = value;

         return this;

       }

       public Builder ClearNanDouble() {

+        PrepareBuilder();

         result.hasNanDouble = false;

         result.nanDouble_ = double.NaN;

         return this;

@@ -14383,11 +15589,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetInfFloat(value); }

       }

       public Builder SetInfFloat(float value) {

+        PrepareBuilder();

         result.hasInfFloat = true;

         result.infFloat_ = value;

         return this;

       }

       public Builder ClearInfFloat() {

+        PrepareBuilder();

         result.hasInfFloat = false;

         result.infFloat_ = float.PositiveInfinity;

         return this;

@@ -14401,11 +15609,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetNegInfFloat(value); }

       }

       public Builder SetNegInfFloat(float value) {

+        PrepareBuilder();

         result.hasNegInfFloat = true;

         result.negInfFloat_ = value;

         return this;

       }

       public Builder ClearNegInfFloat() {

+        PrepareBuilder();

         result.hasNegInfFloat = false;

         result.negInfFloat_ = float.NegativeInfinity;

         return this;

@@ -14419,11 +15629,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetNanFloat(value); }

       }

       public Builder SetNanFloat(float value) {

+        PrepareBuilder();

         result.hasNanFloat = true;

         result.nanFloat_ = value;

         return this;

       }

       public Builder ClearNanFloat() {

+        PrepareBuilder();

         result.hasNanFloat = false;

         result.nanFloat_ = float.NaN;

         return this;

@@ -14537,7 +15749,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(OneString prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -14547,21 +15759,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new OneString();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(OneString cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      OneString result = new OneString();

+      bool builderIsReadOnly;

+      OneString result;

+      

+      private OneString PrepareBuilder() {

+        if (builderIsReadOnly) {

+          OneString original = result;

+          result = new OneString();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override OneString MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new OneString();

+        result = DefaultInstance ?? new OneString();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -14573,12 +15812,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override OneString BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        OneString returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -14592,6 +15830,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(OneString other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.OneString.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasData) {

           Data = other.Data;

         }

@@ -14604,6 +15843,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -14660,11 +15900,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetData(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasData = true;

         result.data_ = value;

         return this;

       }

       public Builder ClearData() {

+        PrepareBuilder();

         result.hasData = false;

         result.data_ = "";

         return this;

@@ -14778,7 +16020,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(OneBytes prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -14788,21 +16030,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new OneBytes();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(OneBytes cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      OneBytes result = new OneBytes();

+      bool builderIsReadOnly;

+      OneBytes result;

+      

+      private OneBytes PrepareBuilder() {

+        if (builderIsReadOnly) {

+          OneBytes original = result;

+          result = new OneBytes();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override OneBytes MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new OneBytes();

+        result = DefaultInstance ?? new OneBytes();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -14814,12 +16083,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override OneBytes BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        OneBytes returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -14833,6 +16101,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(OneBytes other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.OneBytes.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasData) {

           Data = other.Data;

         }

@@ -14845,6 +16114,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -14901,11 +16171,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetData(pb::ByteString value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasData = true;

         result.data_ = value;

         return this;

       }

       public Builder ClearData() {

+        PrepareBuilder();

         result.hasData = false;

         result.data_ = pb::ByteString.Empty;

         return this;

@@ -15376,7 +16648,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestPackedTypes prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -15386,21 +16658,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestPackedTypes();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestPackedTypes cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestPackedTypes result = new TestPackedTypes();

+      bool builderIsReadOnly;

+      TestPackedTypes result;

+      

+      private TestPackedTypes PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestPackedTypes original = result;

+          result = new TestPackedTypes();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestPackedTypes MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestPackedTypes();

+        result = DefaultInstance ?? new TestPackedTypes();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -15412,8 +16711,8 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestPackedTypes BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.packedInt32_.MakeReadOnly();

         result.packedInt64_.MakeReadOnly();

@@ -15429,9 +16728,8 @@ namespace Google.ProtocolBuffers.TestProtos {
         result.packedDouble_.MakeReadOnly();

         result.packedBool_.MakeReadOnly();

         result.packedEnum_.MakeReadOnly();

-        TestPackedTypes returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -15445,6 +16743,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestPackedTypes other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestPackedTypes.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.packedInt32_.Count != 0) {

           result.packedInt32_.Add(other.packedInt32_);

         }

@@ -15496,6 +16795,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -15619,7 +16919,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       

       public pbc::IPopsicleList<int> PackedInt32List {

-        get { return result.packedInt32_; }

+        get { return PrepareBuilder().packedInt32_; }

       }

       public int PackedInt32Count {

         get { return result.PackedInt32Count; }

@@ -15628,24 +16928,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedInt32(index);

       }

       public Builder SetPackedInt32(int index, int value) {

+        PrepareBuilder();

         result.packedInt32_[index] = value;

         return this;

       }

       public Builder AddPackedInt32(int value) {

+        PrepareBuilder();

         result.packedInt32_.Add(value);

         return this;

       }

       public Builder AddRangePackedInt32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.packedInt32_.Add(values);

         return this;

       }

       public Builder ClearPackedInt32() {

+        PrepareBuilder();

         result.packedInt32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> PackedInt64List {

-        get { return result.packedInt64_; }

+        get { return PrepareBuilder().packedInt64_; }

       }

       public int PackedInt64Count {

         get { return result.PackedInt64Count; }

@@ -15654,25 +16958,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedInt64(index);

       }

       public Builder SetPackedInt64(int index, long value) {

+        PrepareBuilder();

         result.packedInt64_[index] = value;

         return this;

       }

       public Builder AddPackedInt64(long value) {

+        PrepareBuilder();

         result.packedInt64_.Add(value);

         return this;

       }

       public Builder AddRangePackedInt64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.packedInt64_.Add(values);

         return this;

       }

       public Builder ClearPackedInt64() {

+        PrepareBuilder();

         result.packedInt64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> PackedUint32List {

-        get { return result.packedUint32_; }

+        get { return PrepareBuilder().packedUint32_; }

       }

       public int PackedUint32Count {

         get { return result.PackedUint32Count; }

@@ -15683,27 +16991,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetPackedUint32(int index, uint value) {

+        PrepareBuilder();

         result.packedUint32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddPackedUint32(uint value) {

+        PrepareBuilder();

         result.packedUint32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangePackedUint32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.packedUint32_.Add(values);

         return this;

       }

       public Builder ClearPackedUint32() {

+        PrepareBuilder();

         result.packedUint32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> PackedUint64List {

-        get { return result.packedUint64_; }

+        get { return PrepareBuilder().packedUint64_; }

       }

       public int PackedUint64Count {

         get { return result.PackedUint64Count; }

@@ -15714,26 +17026,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetPackedUint64(int index, ulong value) {

+        PrepareBuilder();

         result.packedUint64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddPackedUint64(ulong value) {

+        PrepareBuilder();

         result.packedUint64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangePackedUint64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.packedUint64_.Add(values);

         return this;

       }

       public Builder ClearPackedUint64() {

+        PrepareBuilder();

         result.packedUint64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> PackedSint32List {

-        get { return result.packedSint32_; }

+        get { return PrepareBuilder().packedSint32_; }

       }

       public int PackedSint32Count {

         get { return result.PackedSint32Count; }

@@ -15742,24 +17058,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedSint32(index);

       }

       public Builder SetPackedSint32(int index, int value) {

+        PrepareBuilder();

         result.packedSint32_[index] = value;

         return this;

       }

       public Builder AddPackedSint32(int value) {

+        PrepareBuilder();

         result.packedSint32_.Add(value);

         return this;

       }

       public Builder AddRangePackedSint32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.packedSint32_.Add(values);

         return this;

       }

       public Builder ClearPackedSint32() {

+        PrepareBuilder();

         result.packedSint32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> PackedSint64List {

-        get { return result.packedSint64_; }

+        get { return PrepareBuilder().packedSint64_; }

       }

       public int PackedSint64Count {

         get { return result.PackedSint64Count; }

@@ -15768,25 +17088,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedSint64(index);

       }

       public Builder SetPackedSint64(int index, long value) {

+        PrepareBuilder();

         result.packedSint64_[index] = value;

         return this;

       }

       public Builder AddPackedSint64(long value) {

+        PrepareBuilder();

         result.packedSint64_.Add(value);

         return this;

       }

       public Builder AddRangePackedSint64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.packedSint64_.Add(values);

         return this;

       }

       public Builder ClearPackedSint64() {

+        PrepareBuilder();

         result.packedSint64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> PackedFixed32List {

-        get { return result.packedFixed32_; }

+        get { return PrepareBuilder().packedFixed32_; }

       }

       public int PackedFixed32Count {

         get { return result.PackedFixed32Count; }

@@ -15797,27 +17121,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetPackedFixed32(int index, uint value) {

+        PrepareBuilder();

         result.packedFixed32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddPackedFixed32(uint value) {

+        PrepareBuilder();

         result.packedFixed32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangePackedFixed32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.packedFixed32_.Add(values);

         return this;

       }

       public Builder ClearPackedFixed32() {

+        PrepareBuilder();

         result.packedFixed32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> PackedFixed64List {

-        get { return result.packedFixed64_; }

+        get { return PrepareBuilder().packedFixed64_; }

       }

       public int PackedFixed64Count {

         get { return result.PackedFixed64Count; }

@@ -15828,26 +17156,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetPackedFixed64(int index, ulong value) {

+        PrepareBuilder();

         result.packedFixed64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddPackedFixed64(ulong value) {

+        PrepareBuilder();

         result.packedFixed64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangePackedFixed64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.packedFixed64_.Add(values);

         return this;

       }

       public Builder ClearPackedFixed64() {

+        PrepareBuilder();

         result.packedFixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> PackedSfixed32List {

-        get { return result.packedSfixed32_; }

+        get { return PrepareBuilder().packedSfixed32_; }

       }

       public int PackedSfixed32Count {

         get { return result.PackedSfixed32Count; }

@@ -15856,24 +17188,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedSfixed32(index);

       }

       public Builder SetPackedSfixed32(int index, int value) {

+        PrepareBuilder();

         result.packedSfixed32_[index] = value;

         return this;

       }

       public Builder AddPackedSfixed32(int value) {

+        PrepareBuilder();

         result.packedSfixed32_.Add(value);

         return this;

       }

       public Builder AddRangePackedSfixed32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.packedSfixed32_.Add(values);

         return this;

       }

       public Builder ClearPackedSfixed32() {

+        PrepareBuilder();

         result.packedSfixed32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> PackedSfixed64List {

-        get { return result.packedSfixed64_; }

+        get { return PrepareBuilder().packedSfixed64_; }

       }

       public int PackedSfixed64Count {

         get { return result.PackedSfixed64Count; }

@@ -15882,24 +17218,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedSfixed64(index);

       }

       public Builder SetPackedSfixed64(int index, long value) {

+        PrepareBuilder();

         result.packedSfixed64_[index] = value;

         return this;

       }

       public Builder AddPackedSfixed64(long value) {

+        PrepareBuilder();

         result.packedSfixed64_.Add(value);

         return this;

       }

       public Builder AddRangePackedSfixed64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.packedSfixed64_.Add(values);

         return this;

       }

       public Builder ClearPackedSfixed64() {

+        PrepareBuilder();

         result.packedSfixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<float> PackedFloatList {

-        get { return result.packedFloat_; }

+        get { return PrepareBuilder().packedFloat_; }

       }

       public int PackedFloatCount {

         get { return result.PackedFloatCount; }

@@ -15908,24 +17248,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedFloat(index);

       }

       public Builder SetPackedFloat(int index, float value) {

+        PrepareBuilder();

         result.packedFloat_[index] = value;

         return this;

       }

       public Builder AddPackedFloat(float value) {

+        PrepareBuilder();

         result.packedFloat_.Add(value);

         return this;

       }

       public Builder AddRangePackedFloat(scg::IEnumerable<float> values) {

+        PrepareBuilder();

         result.packedFloat_.Add(values);

         return this;

       }

       public Builder ClearPackedFloat() {

+        PrepareBuilder();

         result.packedFloat_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<double> PackedDoubleList {

-        get { return result.packedDouble_; }

+        get { return PrepareBuilder().packedDouble_; }

       }

       public int PackedDoubleCount {

         get { return result.PackedDoubleCount; }

@@ -15934,24 +17278,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedDouble(index);

       }

       public Builder SetPackedDouble(int index, double value) {

+        PrepareBuilder();

         result.packedDouble_[index] = value;

         return this;

       }

       public Builder AddPackedDouble(double value) {

+        PrepareBuilder();

         result.packedDouble_.Add(value);

         return this;

       }

       public Builder AddRangePackedDouble(scg::IEnumerable<double> values) {

+        PrepareBuilder();

         result.packedDouble_.Add(values);

         return this;

       }

       public Builder ClearPackedDouble() {

+        PrepareBuilder();

         result.packedDouble_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<bool> PackedBoolList {

-        get { return result.packedBool_; }

+        get { return PrepareBuilder().packedBool_; }

       }

       public int PackedBoolCount {

         get { return result.PackedBoolCount; }

@@ -15960,24 +17308,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedBool(index);

       }

       public Builder SetPackedBool(int index, bool value) {

+        PrepareBuilder();

         result.packedBool_[index] = value;

         return this;

       }

       public Builder AddPackedBool(bool value) {

+        PrepareBuilder();

         result.packedBool_.Add(value);

         return this;

       }

       public Builder AddRangePackedBool(scg::IEnumerable<bool> values) {

+        PrepareBuilder();

         result.packedBool_.Add(values);

         return this;

       }

       public Builder ClearPackedBool() {

+        PrepareBuilder();

         result.packedBool_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> PackedEnumList {

-        get { return result.packedEnum_; }

+        get { return PrepareBuilder().packedEnum_; }

       }

       public int PackedEnumCount {

         get { return result.PackedEnumCount; }

@@ -15986,18 +17338,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedEnum(index);

       }

       public Builder SetPackedEnum(int index, global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.packedEnum_[index] = value;

         return this;

       }

       public Builder AddPackedEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.packedEnum_.Add(value);

         return this;

       }

       public Builder AddRangePackedEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> values) {

+        PrepareBuilder();

         result.packedEnum_.Add(values);

         return this;

       }

       public Builder ClearPackedEnum() {

+        PrepareBuilder();

         result.packedEnum_.Clear();

         return this;

       }

@@ -16412,7 +17768,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestUnpackedTypes prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -16422,21 +17778,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestUnpackedTypes();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestUnpackedTypes cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestUnpackedTypes result;

+      

+      private TestUnpackedTypes PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestUnpackedTypes original = result;

+          result = new TestUnpackedTypes();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestUnpackedTypes result = new TestUnpackedTypes();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestUnpackedTypes MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestUnpackedTypes();

+        result = DefaultInstance ?? new TestUnpackedTypes();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -16448,8 +17831,8 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestUnpackedTypes BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.unpackedInt32_.MakeReadOnly();

         result.unpackedInt64_.MakeReadOnly();

@@ -16465,9 +17848,8 @@ namespace Google.ProtocolBuffers.TestProtos {
         result.unpackedDouble_.MakeReadOnly();

         result.unpackedBool_.MakeReadOnly();

         result.unpackedEnum_.MakeReadOnly();

-        TestUnpackedTypes returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -16481,6 +17863,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestUnpackedTypes other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestUnpackedTypes.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.unpackedInt32_.Count != 0) {

           result.unpackedInt32_.Add(other.unpackedInt32_);

         }

@@ -16532,6 +17915,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -16655,7 +18039,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       

       public pbc::IPopsicleList<int> UnpackedInt32List {

-        get { return result.unpackedInt32_; }

+        get { return PrepareBuilder().unpackedInt32_; }

       }

       public int UnpackedInt32Count {

         get { return result.UnpackedInt32Count; }

@@ -16664,24 +18048,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedInt32(index);

       }

       public Builder SetUnpackedInt32(int index, int value) {

+        PrepareBuilder();

         result.unpackedInt32_[index] = value;

         return this;

       }

       public Builder AddUnpackedInt32(int value) {

+        PrepareBuilder();

         result.unpackedInt32_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedInt32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.unpackedInt32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedInt32() {

+        PrepareBuilder();

         result.unpackedInt32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> UnpackedInt64List {

-        get { return result.unpackedInt64_; }

+        get { return PrepareBuilder().unpackedInt64_; }

       }

       public int UnpackedInt64Count {

         get { return result.UnpackedInt64Count; }

@@ -16690,25 +18078,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedInt64(index);

       }

       public Builder SetUnpackedInt64(int index, long value) {

+        PrepareBuilder();

         result.unpackedInt64_[index] = value;

         return this;

       }

       public Builder AddUnpackedInt64(long value) {

+        PrepareBuilder();

         result.unpackedInt64_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedInt64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.unpackedInt64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedInt64() {

+        PrepareBuilder();

         result.unpackedInt64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> UnpackedUint32List {

-        get { return result.unpackedUint32_; }

+        get { return PrepareBuilder().unpackedUint32_; }

       }

       public int UnpackedUint32Count {

         get { return result.UnpackedUint32Count; }

@@ -16719,27 +18111,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetUnpackedUint32(int index, uint value) {

+        PrepareBuilder();

         result.unpackedUint32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddUnpackedUint32(uint value) {

+        PrepareBuilder();

         result.unpackedUint32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeUnpackedUint32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.unpackedUint32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedUint32() {

+        PrepareBuilder();

         result.unpackedUint32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> UnpackedUint64List {

-        get { return result.unpackedUint64_; }

+        get { return PrepareBuilder().unpackedUint64_; }

       }

       public int UnpackedUint64Count {

         get { return result.UnpackedUint64Count; }

@@ -16750,26 +18146,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetUnpackedUint64(int index, ulong value) {

+        PrepareBuilder();

         result.unpackedUint64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddUnpackedUint64(ulong value) {

+        PrepareBuilder();

         result.unpackedUint64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeUnpackedUint64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.unpackedUint64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedUint64() {

+        PrepareBuilder();

         result.unpackedUint64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> UnpackedSint32List {

-        get { return result.unpackedSint32_; }

+        get { return PrepareBuilder().unpackedSint32_; }

       }

       public int UnpackedSint32Count {

         get { return result.UnpackedSint32Count; }

@@ -16778,24 +18178,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedSint32(index);

       }

       public Builder SetUnpackedSint32(int index, int value) {

+        PrepareBuilder();

         result.unpackedSint32_[index] = value;

         return this;

       }

       public Builder AddUnpackedSint32(int value) {

+        PrepareBuilder();

         result.unpackedSint32_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedSint32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.unpackedSint32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedSint32() {

+        PrepareBuilder();

         result.unpackedSint32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> UnpackedSint64List {

-        get { return result.unpackedSint64_; }

+        get { return PrepareBuilder().unpackedSint64_; }

       }

       public int UnpackedSint64Count {

         get { return result.UnpackedSint64Count; }

@@ -16804,25 +18208,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedSint64(index);

       }

       public Builder SetUnpackedSint64(int index, long value) {

+        PrepareBuilder();

         result.unpackedSint64_[index] = value;

         return this;

       }

       public Builder AddUnpackedSint64(long value) {

+        PrepareBuilder();

         result.unpackedSint64_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedSint64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.unpackedSint64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedSint64() {

+        PrepareBuilder();

         result.unpackedSint64_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> UnpackedFixed32List {

-        get { return result.unpackedFixed32_; }

+        get { return PrepareBuilder().unpackedFixed32_; }

       }

       public int UnpackedFixed32Count {

         get { return result.UnpackedFixed32Count; }

@@ -16833,27 +18241,31 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetUnpackedFixed32(int index, uint value) {

+        PrepareBuilder();

         result.unpackedFixed32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddUnpackedFixed32(uint value) {

+        PrepareBuilder();

         result.unpackedFixed32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeUnpackedFixed32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.unpackedFixed32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedFixed32() {

+        PrepareBuilder();

         result.unpackedFixed32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> UnpackedFixed64List {

-        get { return result.unpackedFixed64_; }

+        get { return PrepareBuilder().unpackedFixed64_; }

       }

       public int UnpackedFixed64Count {

         get { return result.UnpackedFixed64Count; }

@@ -16864,26 +18276,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetUnpackedFixed64(int index, ulong value) {

+        PrepareBuilder();

         result.unpackedFixed64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddUnpackedFixed64(ulong value) {

+        PrepareBuilder();

         result.unpackedFixed64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeUnpackedFixed64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.unpackedFixed64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedFixed64() {

+        PrepareBuilder();

         result.unpackedFixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> UnpackedSfixed32List {

-        get { return result.unpackedSfixed32_; }

+        get { return PrepareBuilder().unpackedSfixed32_; }

       }

       public int UnpackedSfixed32Count {

         get { return result.UnpackedSfixed32Count; }

@@ -16892,24 +18308,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedSfixed32(index);

       }

       public Builder SetUnpackedSfixed32(int index, int value) {

+        PrepareBuilder();

         result.unpackedSfixed32_[index] = value;

         return this;

       }

       public Builder AddUnpackedSfixed32(int value) {

+        PrepareBuilder();

         result.unpackedSfixed32_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedSfixed32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.unpackedSfixed32_.Add(values);

         return this;

       }

       public Builder ClearUnpackedSfixed32() {

+        PrepareBuilder();

         result.unpackedSfixed32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> UnpackedSfixed64List {

-        get { return result.unpackedSfixed64_; }

+        get { return PrepareBuilder().unpackedSfixed64_; }

       }

       public int UnpackedSfixed64Count {

         get { return result.UnpackedSfixed64Count; }

@@ -16918,24 +18338,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedSfixed64(index);

       }

       public Builder SetUnpackedSfixed64(int index, long value) {

+        PrepareBuilder();

         result.unpackedSfixed64_[index] = value;

         return this;

       }

       public Builder AddUnpackedSfixed64(long value) {

+        PrepareBuilder();

         result.unpackedSfixed64_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedSfixed64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.unpackedSfixed64_.Add(values);

         return this;

       }

       public Builder ClearUnpackedSfixed64() {

+        PrepareBuilder();

         result.unpackedSfixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<float> UnpackedFloatList {

-        get { return result.unpackedFloat_; }

+        get { return PrepareBuilder().unpackedFloat_; }

       }

       public int UnpackedFloatCount {

         get { return result.UnpackedFloatCount; }

@@ -16944,24 +18368,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedFloat(index);

       }

       public Builder SetUnpackedFloat(int index, float value) {

+        PrepareBuilder();

         result.unpackedFloat_[index] = value;

         return this;

       }

       public Builder AddUnpackedFloat(float value) {

+        PrepareBuilder();

         result.unpackedFloat_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedFloat(scg::IEnumerable<float> values) {

+        PrepareBuilder();

         result.unpackedFloat_.Add(values);

         return this;

       }

       public Builder ClearUnpackedFloat() {

+        PrepareBuilder();

         result.unpackedFloat_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<double> UnpackedDoubleList {

-        get { return result.unpackedDouble_; }

+        get { return PrepareBuilder().unpackedDouble_; }

       }

       public int UnpackedDoubleCount {

         get { return result.UnpackedDoubleCount; }

@@ -16970,24 +18398,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedDouble(index);

       }

       public Builder SetUnpackedDouble(int index, double value) {

+        PrepareBuilder();

         result.unpackedDouble_[index] = value;

         return this;

       }

       public Builder AddUnpackedDouble(double value) {

+        PrepareBuilder();

         result.unpackedDouble_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedDouble(scg::IEnumerable<double> values) {

+        PrepareBuilder();

         result.unpackedDouble_.Add(values);

         return this;

       }

       public Builder ClearUnpackedDouble() {

+        PrepareBuilder();

         result.unpackedDouble_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<bool> UnpackedBoolList {

-        get { return result.unpackedBool_; }

+        get { return PrepareBuilder().unpackedBool_; }

       }

       public int UnpackedBoolCount {

         get { return result.UnpackedBoolCount; }

@@ -16996,24 +18428,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedBool(index);

       }

       public Builder SetUnpackedBool(int index, bool value) {

+        PrepareBuilder();

         result.unpackedBool_[index] = value;

         return this;

       }

       public Builder AddUnpackedBool(bool value) {

+        PrepareBuilder();

         result.unpackedBool_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedBool(scg::IEnumerable<bool> values) {

+        PrepareBuilder();

         result.unpackedBool_.Add(values);

         return this;

       }

       public Builder ClearUnpackedBool() {

+        PrepareBuilder();

         result.unpackedBool_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> UnpackedEnumList {

-        get { return result.unpackedEnum_; }

+        get { return PrepareBuilder().unpackedEnum_; }

       }

       public int UnpackedEnumCount {

         get { return result.UnpackedEnumCount; }

@@ -17022,18 +18458,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetUnpackedEnum(index);

       }

       public Builder SetUnpackedEnum(int index, global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.unpackedEnum_[index] = value;

         return this;

       }

       public Builder AddUnpackedEnum(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.unpackedEnum_.Add(value);

         return this;

       }

       public Builder AddRangeUnpackedEnum(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignEnum> values) {

+        PrepareBuilder();

         result.unpackedEnum_.Add(values);

         return this;

       }

       public Builder ClearUnpackedEnum() {

+        PrepareBuilder();

         result.unpackedEnum_.Clear();

         return this;

       }

@@ -17134,7 +18574,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestPackedExtensions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -17144,21 +18584,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestPackedExtensions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestPackedExtensions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestPackedExtensions result;

+      

+      private TestPackedExtensions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestPackedExtensions original = result;

+          result = new TestPackedExtensions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestPackedExtensions result = new TestPackedExtensions();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestPackedExtensions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestPackedExtensions();

+        result = DefaultInstance ?? new TestPackedExtensions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -17170,12 +18637,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestPackedExtensions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestPackedExtensions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -17189,6 +18655,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestPackedExtensions other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestPackedExtensions.DefaultInstance) return this;

+        PrepareBuilder();

           this.MergeExtensionFields(other);

         this.MergeUnknownFields(other.UnknownFields);

         return this;

@@ -17199,6 +18666,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -17338,7 +18806,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestUnpackedExtensions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -17348,21 +18816,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestUnpackedExtensions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestUnpackedExtensions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestUnpackedExtensions result;

+      

+      private TestUnpackedExtensions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestUnpackedExtensions original = result;

+          result = new TestUnpackedExtensions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestUnpackedExtensions result = new TestUnpackedExtensions();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestUnpackedExtensions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestUnpackedExtensions();

+        result = DefaultInstance ?? new TestUnpackedExtensions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -17374,12 +18869,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestUnpackedExtensions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        TestUnpackedExtensions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -17393,6 +18887,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestUnpackedExtensions other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestUnpackedExtensions.DefaultInstance) return this;

+        PrepareBuilder();

           this.MergeExtensionFields(other);

         this.MergeUnknownFields(other.UnknownFields);

         return this;

@@ -17403,6 +18898,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -17595,7 +19091,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         public override Builder ToBuilder() { return CreateBuilder(this); }

         public override Builder CreateBuilderForType() { return new Builder(); }

         public static Builder CreateBuilder(DynamicMessageType prototype) {

-          return (Builder) new Builder().MergeFrom(prototype);

+          return new Builder(prototype);

         }

         

         [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -17605,21 +19101,48 @@ namespace Google.ProtocolBuffers.TestProtos {
           protected override Builder ThisBuilder {

             get { return this; }

           }

-          public Builder() {}

+          public Builder() {

+            result = DefaultInstance ?? new DynamicMessageType();

+            builderIsReadOnly = result == DefaultInstance;

+          }

+          internal Builder(DynamicMessageType cloneFrom) {

+            result = cloneFrom;

+            builderIsReadOnly = true;

+          }

+          

+          bool builderIsReadOnly;

+          DynamicMessageType result;

           

-          DynamicMessageType result = new DynamicMessageType();

+          private DynamicMessageType PrepareBuilder() {

+            if (builderIsReadOnly) {

+              DynamicMessageType original = result;

+              result = new DynamicMessageType();

+              builderIsReadOnly = false;

+              MergeFrom(original);

+            }

+            return result;

+          }

+          

+          public override bool IsInitialized {

+            get { return result.IsInitialized; }

+          }

           

           protected override DynamicMessageType MessageBeingBuilt {

-            get { return result; }

+            get { return PrepareBuilder(); }

           }

           

           public override Builder Clear() {

-            result = new DynamicMessageType();

+            result = DefaultInstance ?? new DynamicMessageType();

+            builderIsReadOnly = true;

             return this;

           }

           

           public override Builder Clone() {

-            return new Builder().MergeFrom(result);

+            if (builderIsReadOnly) {

+              return new Builder(result);

+            } else {

+              return new Builder().MergeFrom(result);

+            }

           }

           

           public override pbd::MessageDescriptor DescriptorForType {

@@ -17631,12 +19154,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override DynamicMessageType BuildPartial() {

-            if (result == null) {

-              throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+            if (builderIsReadOnly) {

+              return result;

             }

-            DynamicMessageType returnMe = result;

-            result = null;

-            return returnMe;

+            builderIsReadOnly = true;

+            return result;

           }

           

           public override Builder MergeFrom(pb::IMessage other) {

@@ -17650,6 +19172,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           

           public override Builder MergeFrom(DynamicMessageType other) {

             if (other == global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType.DefaultInstance) return this;

+            PrepareBuilder();

             if (other.HasDynamicField) {

               DynamicField = other.DynamicField;

             }

@@ -17662,6 +19185,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           }

           

           public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+            PrepareBuilder();

             pb::UnknownFieldSet.Builder unknownFields = null;

             uint tag;

             string field_name;

@@ -17717,11 +19241,13 @@ namespace Google.ProtocolBuffers.TestProtos {
             set { SetDynamicField(value); }

           }

           public Builder SetDynamicField(int value) {

+            PrepareBuilder();

             result.hasDynamicField = true;

             result.dynamicField_ = value;

             return this;

           }

           public Builder ClearDynamicField() {

+            PrepareBuilder();

             result.hasDynamicField = false;

             result.dynamicField_ = 0;

             return this;

@@ -17925,7 +19451,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestDynamicExtensions prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -17935,21 +19461,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestDynamicExtensions();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestDynamicExtensions cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      TestDynamicExtensions result = new TestDynamicExtensions();

+      bool builderIsReadOnly;

+      TestDynamicExtensions result;

+      

+      private TestDynamicExtensions PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestDynamicExtensions original = result;

+          result = new TestDynamicExtensions();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestDynamicExtensions MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestDynamicExtensions();

+        result = DefaultInstance ?? new TestDynamicExtensions();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -17961,14 +19514,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestDynamicExtensions BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.repeatedExtension_.MakeReadOnly();

         result.packedExtension_.MakeReadOnly();

-        TestDynamicExtensions returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -17982,6 +19534,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestDynamicExtensions other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.HasScalarExtension) {

           ScalarExtension = other.ScalarExtension;

         }

@@ -18012,6 +19565,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -18120,11 +19674,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetScalarExtension(uint value) {

+        PrepareBuilder();

         result.hasScalarExtension = true;

         result.scalarExtension_ = value;

         return this;

       }

       public Builder ClearScalarExtension() {

+        PrepareBuilder();

         result.hasScalarExtension = false;

         result.scalarExtension_ = 0;

         return this;

@@ -18138,11 +19694,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetEnumExtension(value); }

       }

       public Builder SetEnumExtension(global::Google.ProtocolBuffers.TestProtos.ForeignEnum value) {

+        PrepareBuilder();

         result.hasEnumExtension = true;

         result.enumExtension_ = value;

         return this;

       }

       public Builder ClearEnumExtension() {

+        PrepareBuilder();

         result.hasEnumExtension = false;

         result.enumExtension_ = global::Google.ProtocolBuffers.TestProtos.ForeignEnum.FOREIGN_FOO;

         return this;

@@ -18156,11 +19714,13 @@ namespace Google.ProtocolBuffers.TestProtos {
         set { SetDynamicEnumExtension(value); }

       }

       public Builder SetDynamicEnumExtension(global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicEnumType value) {

+        PrepareBuilder();

         result.hasDynamicEnumExtension = true;

         result.dynamicEnumExtension_ = value;

         return this;

       }

       public Builder ClearDynamicEnumExtension() {

+        PrepareBuilder();

         result.hasDynamicEnumExtension = false;

         result.dynamicEnumExtension_ = global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicEnumType.DYNAMIC_FOO;

         return this;

@@ -18175,18 +19735,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetMessageExtension(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasMessageExtension = true;

         result.messageExtension_ = value;

         return this;

       }

       public Builder SetMessageExtension(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasMessageExtension = true;

         result.messageExtension_ = builderForValue.Build();

         return this;

       }

       public Builder MergeMessageExtension(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasMessageExtension &&

             result.messageExtension_ != global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance) {

             result.messageExtension_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.CreateBuilder(result.messageExtension_).MergeFrom(value).BuildPartial();

@@ -18197,6 +19760,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearMessageExtension() {

+        PrepareBuilder();

         result.hasMessageExtension = false;

         result.messageExtension_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance;

         return this;

@@ -18211,18 +19775,21 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetDynamicMessageExtension(global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.hasDynamicMessageExtension = true;

         result.dynamicMessageExtension_ = value;

         return this;

       }

       public Builder SetDynamicMessageExtension(global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType.Builder builderForValue) {

         pb::ThrowHelper.ThrowIfNull(builderForValue, "builderForValue");

+        PrepareBuilder();

         result.hasDynamicMessageExtension = true;

         result.dynamicMessageExtension_ = builderForValue.Build();

         return this;

       }

       public Builder MergeDynamicMessageExtension(global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         if (result.hasDynamicMessageExtension &&

             result.dynamicMessageExtension_ != global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType.DefaultInstance) {

             result.dynamicMessageExtension_ = global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType.CreateBuilder(result.dynamicMessageExtension_).MergeFrom(value).BuildPartial();

@@ -18233,13 +19800,14 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;

       }

       public Builder ClearDynamicMessageExtension() {

+        PrepareBuilder();

         result.hasDynamicMessageExtension = false;

         result.dynamicMessageExtension_ = global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType.DefaultInstance;

         return this;

       }

       

       public pbc::IPopsicleList<string> RepeatedExtensionList {

-        get { return result.repeatedExtension_; }

+        get { return PrepareBuilder().repeatedExtension_; }

       }

       public int RepeatedExtensionCount {

         get { return result.RepeatedExtensionCount; }

@@ -18249,25 +19817,29 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       public Builder SetRepeatedExtension(int index, string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedExtension_[index] = value;

         return this;

       }

       public Builder AddRepeatedExtension(string value) {

         pb::ThrowHelper.ThrowIfNull(value, "value");

+        PrepareBuilder();

         result.repeatedExtension_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedExtension(scg::IEnumerable<string> values) {

+        PrepareBuilder();

         result.repeatedExtension_.Add(values);

         return this;

       }

       public Builder ClearRepeatedExtension() {

+        PrepareBuilder();

         result.repeatedExtension_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> PackedExtensionList {

-        get { return result.packedExtension_; }

+        get { return PrepareBuilder().packedExtension_; }

       }

       public int PackedExtensionCount {

         get { return result.PackedExtensionCount; }

@@ -18276,18 +19848,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetPackedExtension(index);

       }

       public Builder SetPackedExtension(int index, int value) {

+        PrepareBuilder();

         result.packedExtension_[index] = value;

         return this;

       }

       public Builder AddPackedExtension(int value) {

+        PrepareBuilder();

         result.packedExtension_.Add(value);

         return this;

       }

       public Builder AddRangePackedExtension(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.packedExtension_.Add(values);

         return this;

       }

       public Builder ClearPackedExtension() {

+        PrepareBuilder();

         result.packedExtension_.Clear();

         return this;

       }

@@ -18522,7 +20098,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(TestRepeatedScalarDifferentTagSizes prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -18532,21 +20108,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new TestRepeatedScalarDifferentTagSizes();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(TestRepeatedScalarDifferentTagSizes cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      TestRepeatedScalarDifferentTagSizes result;

+      

+      private TestRepeatedScalarDifferentTagSizes PrepareBuilder() {

+        if (builderIsReadOnly) {

+          TestRepeatedScalarDifferentTagSizes original = result;

+          result = new TestRepeatedScalarDifferentTagSizes();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      TestRepeatedScalarDifferentTagSizes result = new TestRepeatedScalarDifferentTagSizes();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override TestRepeatedScalarDifferentTagSizes MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new TestRepeatedScalarDifferentTagSizes();

+        result = DefaultInstance ?? new TestRepeatedScalarDifferentTagSizes();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -18558,8 +20161,8 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override TestRepeatedScalarDifferentTagSizes BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

         result.repeatedFixed32_.MakeReadOnly();

         result.repeatedInt32_.MakeReadOnly();

@@ -18567,9 +20170,8 @@ namespace Google.ProtocolBuffers.TestProtos {
         result.repeatedInt64_.MakeReadOnly();

         result.repeatedFloat_.MakeReadOnly();

         result.repeatedUint64_.MakeReadOnly();

-        TestRepeatedScalarDifferentTagSizes returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -18583,6 +20185,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(TestRepeatedScalarDifferentTagSizes other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.TestRepeatedScalarDifferentTagSizes.DefaultInstance) return this;

+        PrepareBuilder();

         if (other.repeatedFixed32_.Count != 0) {

           result.repeatedFixed32_.Add(other.repeatedFixed32_);

         }

@@ -18610,6 +20213,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -18685,7 +20289,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<uint> RepeatedFixed32List {

-        get { return result.repeatedFixed32_; }

+        get { return PrepareBuilder().repeatedFixed32_; }

       }

       public int RepeatedFixed32Count {

         get { return result.RepeatedFixed32Count; }

@@ -18696,26 +20300,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedFixed32(int index, uint value) {

+        PrepareBuilder();

         result.repeatedFixed32_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedFixed32(uint value) {

+        PrepareBuilder();

         result.repeatedFixed32_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedFixed32(scg::IEnumerable<uint> values) {

+        PrepareBuilder();

         result.repeatedFixed32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFixed32() {

+        PrepareBuilder();

         result.repeatedFixed32_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<int> RepeatedInt32List {

-        get { return result.repeatedInt32_; }

+        get { return PrepareBuilder().repeatedInt32_; }

       }

       public int RepeatedInt32Count {

         get { return result.RepeatedInt32Count; }

@@ -18724,25 +20332,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedInt32(index);

       }

       public Builder SetRepeatedInt32(int index, int value) {

+        PrepareBuilder();

         result.repeatedInt32_[index] = value;

         return this;

       }

       public Builder AddRepeatedInt32(int value) {

+        PrepareBuilder();

         result.repeatedInt32_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedInt32(scg::IEnumerable<int> values) {

+        PrepareBuilder();

         result.repeatedInt32_.Add(values);

         return this;

       }

       public Builder ClearRepeatedInt32() {

+        PrepareBuilder();

         result.repeatedInt32_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> RepeatedFixed64List {

-        get { return result.repeatedFixed64_; }

+        get { return PrepareBuilder().repeatedFixed64_; }

       }

       public int RepeatedFixed64Count {

         get { return result.RepeatedFixed64Count; }

@@ -18753,26 +20365,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedFixed64(int index, ulong value) {

+        PrepareBuilder();

         result.repeatedFixed64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedFixed64(ulong value) {

+        PrepareBuilder();

         result.repeatedFixed64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedFixed64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.repeatedFixed64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFixed64() {

+        PrepareBuilder();

         result.repeatedFixed64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<long> RepeatedInt64List {

-        get { return result.repeatedInt64_; }

+        get { return PrepareBuilder().repeatedInt64_; }

       }

       public int RepeatedInt64Count {

         get { return result.RepeatedInt64Count; }

@@ -18781,24 +20397,28 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedInt64(index);

       }

       public Builder SetRepeatedInt64(int index, long value) {

+        PrepareBuilder();

         result.repeatedInt64_[index] = value;

         return this;

       }

       public Builder AddRepeatedInt64(long value) {

+        PrepareBuilder();

         result.repeatedInt64_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedInt64(scg::IEnumerable<long> values) {

+        PrepareBuilder();

         result.repeatedInt64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedInt64() {

+        PrepareBuilder();

         result.repeatedInt64_.Clear();

         return this;

       }

       

       public pbc::IPopsicleList<float> RepeatedFloatList {

-        get { return result.repeatedFloat_; }

+        get { return PrepareBuilder().repeatedFloat_; }

       }

       public int RepeatedFloatCount {

         get { return result.RepeatedFloatCount; }

@@ -18807,25 +20427,29 @@ namespace Google.ProtocolBuffers.TestProtos {
         return result.GetRepeatedFloat(index);

       }

       public Builder SetRepeatedFloat(int index, float value) {

+        PrepareBuilder();

         result.repeatedFloat_[index] = value;

         return this;

       }

       public Builder AddRepeatedFloat(float value) {

+        PrepareBuilder();

         result.repeatedFloat_.Add(value);

         return this;

       }

       public Builder AddRangeRepeatedFloat(scg::IEnumerable<float> values) {

+        PrepareBuilder();

         result.repeatedFloat_.Add(values);

         return this;

       }

       public Builder ClearRepeatedFloat() {

+        PrepareBuilder();

         result.repeatedFloat_.Clear();

         return this;

       }

       

       [global::System.CLSCompliant(false)]

       public pbc::IPopsicleList<ulong> RepeatedUint64List {

-        get { return result.repeatedUint64_; }

+        get { return PrepareBuilder().repeatedUint64_; }

       }

       public int RepeatedUint64Count {

         get { return result.RepeatedUint64Count; }

@@ -18836,20 +20460,24 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       [global::System.CLSCompliant(false)]

       public Builder SetRepeatedUint64(int index, ulong value) {

+        PrepareBuilder();

         result.repeatedUint64_[index] = value;

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRepeatedUint64(ulong value) {

+        PrepareBuilder();

         result.repeatedUint64_.Add(value);

         return this;

       }

       [global::System.CLSCompliant(false)]

       public Builder AddRangeRepeatedUint64(scg::IEnumerable<ulong> values) {

+        PrepareBuilder();

         result.repeatedUint64_.Add(values);

         return this;

       }

       public Builder ClearRepeatedUint64() {

+        PrepareBuilder();

         result.repeatedUint64_.Clear();

         return this;

       }

@@ -18946,7 +20574,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(FooRequest prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -18956,21 +20584,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new FooRequest();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(FooRequest cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      FooRequest result = new FooRequest();

+      bool builderIsReadOnly;

+      FooRequest result;

+      

+      private FooRequest PrepareBuilder() {

+        if (builderIsReadOnly) {

+          FooRequest original = result;

+          result = new FooRequest();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override FooRequest MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new FooRequest();

+        result = DefaultInstance ?? new FooRequest();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -18982,12 +20637,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override FooRequest BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        FooRequest returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -19001,6 +20655,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(FooRequest other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.FooRequest.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -19010,6 +20665,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -19145,7 +20801,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(FooResponse prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -19155,21 +20811,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new FooResponse();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(FooResponse cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      FooResponse result;

+      

+      private FooResponse PrepareBuilder() {

+        if (builderIsReadOnly) {

+          FooResponse original = result;

+          result = new FooResponse();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      FooResponse result = new FooResponse();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override FooResponse MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new FooResponse();

+        result = DefaultInstance ?? new FooResponse();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -19181,12 +20864,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override FooResponse BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        FooResponse returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -19200,6 +20882,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(FooResponse other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.FooResponse.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -19209,6 +20892,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -19344,7 +21028,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(BarRequest prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -19354,21 +21038,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new BarRequest();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(BarRequest cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

+      

+      bool builderIsReadOnly;

+      BarRequest result;

+      

+      private BarRequest PrepareBuilder() {

+        if (builderIsReadOnly) {

+          BarRequest original = result;

+          result = new BarRequest();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

       

-      BarRequest result = new BarRequest();

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override BarRequest MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new BarRequest();

+        result = DefaultInstance ?? new BarRequest();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -19380,12 +21091,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override BarRequest BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        BarRequest returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -19399,6 +21109,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(BarRequest other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.BarRequest.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -19408,6 +21119,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;

@@ -19543,7 +21255,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     public override Builder ToBuilder() { return CreateBuilder(this); }

     public override Builder CreateBuilderForType() { return new Builder(); }

     public static Builder CreateBuilder(BarResponse prototype) {

-      return (Builder) new Builder().MergeFrom(prototype);

+      return new Builder(prototype);

     }

     

     [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

@@ -19553,21 +21265,48 @@ namespace Google.ProtocolBuffers.TestProtos {
       protected override Builder ThisBuilder {

         get { return this; }

       }

-      public Builder() {}

+      public Builder() {

+        result = DefaultInstance ?? new BarResponse();

+        builderIsReadOnly = result == DefaultInstance;

+      }

+      internal Builder(BarResponse cloneFrom) {

+        result = cloneFrom;

+        builderIsReadOnly = true;

+      }

       

-      BarResponse result = new BarResponse();

+      bool builderIsReadOnly;

+      BarResponse result;

+      

+      private BarResponse PrepareBuilder() {

+        if (builderIsReadOnly) {

+          BarResponse original = result;

+          result = new BarResponse();

+          builderIsReadOnly = false;

+          MergeFrom(original);

+        }

+        return result;

+      }

+      

+      public override bool IsInitialized {

+        get { return result.IsInitialized; }

+      }

       

       protected override BarResponse MessageBeingBuilt {

-        get { return result; }

+        get { return PrepareBuilder(); }

       }

       

       public override Builder Clear() {

-        result = new BarResponse();

+        result = DefaultInstance ?? new BarResponse();

+        builderIsReadOnly = true;

         return this;

       }

       

       public override Builder Clone() {

-        return new Builder().MergeFrom(result);

+        if (builderIsReadOnly) {

+          return new Builder(result);

+        } else {

+          return new Builder().MergeFrom(result);

+        }

       }

       

       public override pbd::MessageDescriptor DescriptorForType {

@@ -19579,12 +21318,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override BarResponse BuildPartial() {

-        if (result == null) {

-          throw new global::System.InvalidOperationException("build() has already been called on this Builder");

+        if (builderIsReadOnly) {

+          return result;

         }

-        BarResponse returnMe = result;

-        result = null;

-        return returnMe;

+        builderIsReadOnly = true;

+        return result;

       }

       

       public override Builder MergeFrom(pb::IMessage other) {

@@ -19598,6 +21336,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       

       public override Builder MergeFrom(BarResponse other) {

         if (other == global::Google.ProtocolBuffers.TestProtos.BarResponse.DefaultInstance) return this;

+        PrepareBuilder();

         this.MergeUnknownFields(other.UnknownFields);

         return this;

       }

@@ -19607,6 +21346,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }

       

       public override Builder MergeFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {

+        PrepareBuilder();

         pb::UnknownFieldSet.Builder unknownFields = null;

         uint tag;

         string field_name;