merged issue-22

7 files changed, 3918 insertions, 910 deletions

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;