Regenerated code with changes

author: csharptest <roger@csharptest.net> 2011-09-23 11:14:01 -0500
committer: rogerk <devnull@localhost> 2011-09-23 11:14:01 -0500
commit: a314d4c9fa70c2b22bae02fa22a5dc2dba1db067 (patch)
tree: a8c75a9eff5bfff65ce537f65d529a7b8e93683d /src/ProtocolBuffersLite.Test
parent: dc24b605e356dbfda692e952807b404cccf245bc (diff)
download: protobuf-a314d4c9fa70c2b22bae02fa22a5dc2dba1db067.tar.gz
protobuf-a314d4c9fa70c2b22bae02fa22a5dc2dba1db067.tar.bz2
protobuf-a314d4c9fa70c2b22bae02fa22a5dc2dba1db067.zip
7 files changed, 1544 insertions, 1260 deletions
diff --git a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasFullProtoFile.cs b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasFullProtoFile.cs
index 563cea5e..5267bf36 100644
--- a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasFullProtoFile.cs
+++ b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasFullProtoFile.cs
@@ -128,13 +128,13 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestInteropPerson : pb::ExtendableMessage<TestInteropPerson, TestInteropPerson.Builder> {
-    private static readonly TestInteropPerson defaultInstance = new Builder().BuildPartial();
+    private static readonly TestInteropPerson defaultInstance = new TestInteropPerson().MakeReadOnly();
     public static TestInteropPerson DefaultInstance {
       get { return defaultInstance; }
     }
     
     public override TestInteropPerson DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestInteropPerson ThisMessage {
@@ -166,13 +166,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class PhoneNumber : pb::GeneratedMessage<PhoneNumber, PhoneNumber.Builder> {
-        private static readonly PhoneNumber defaultInstance = new Builder().BuildPartial();
+        private static readonly PhoneNumber defaultInstance = new PhoneNumber().MakeReadOnly();
         public static PhoneNumber DefaultInstance {
           get { return defaultInstance; }
         }
         
         public override PhoneNumber DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override PhoneNumber ThisMessage {
@@ -237,6 +237,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static PhoneNumber ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private PhoneNumber MakeReadOnly() {
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -252,22 +256,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new PhoneNumber();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(PhoneNumber cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          PhoneNumber result;
+          private bool resultIsReadOnly;
+          private PhoneNumber result;
           
           private PhoneNumber PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               PhoneNumber original = result;
               result = new PhoneNumber();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -282,13 +286,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new PhoneNumber();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -304,11 +308,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override PhoneNumber BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           
@@ -362,13 +366,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class Addresses : pb::GeneratedMessage<Addresses, Addresses.Builder> {
-        private static readonly Addresses defaultInstance = new Builder().BuildPartial();
+        private static readonly Addresses defaultInstance = new Addresses().MakeReadOnly();
         public static Addresses DefaultInstance {
           get { return defaultInstance; }
         }
         
         public override Addresses DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override Addresses ThisMessage {
@@ -464,6 +468,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static Addresses ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private Addresses MakeReadOnly() {
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -479,22 +487,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new Addresses();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(Addresses cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          Addresses result;
+          private bool resultIsReadOnly;
+          private Addresses result;
           
           private Addresses PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               Addresses original = result;
               result = new Addresses();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -509,13 +517,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new Addresses();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -531,11 +539,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Addresses BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           
@@ -749,6 +757,13 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestInteropPerson ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestInteropPerson MakeReadOnly() {
+      codes_.MakeReadOnly();
+      phone_.MakeReadOnly();
+      addresses_.MakeReadOnly();
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -764,22 +779,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestInteropPerson();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestInteropPerson cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestInteropPerson result;
+      private bool resultIsReadOnly;
+      private TestInteropPerson result;
       
       private TestInteropPerson PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestInteropPerson original = result;
           result = new TestInteropPerson();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -794,13 +809,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestInteropPerson();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -816,14 +831,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestInteropPerson BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        result.codes_.MakeReadOnly();
-        result.phone_.MakeReadOnly();
-        result.addresses_.MakeReadOnly();
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       
@@ -1016,13 +1028,13 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestInteropEmployeeId : pb::GeneratedMessage<TestInteropEmployeeId, TestInteropEmployeeId.Builder> {
-    private static readonly TestInteropEmployeeId defaultInstance = new Builder().BuildPartial();
+    private static readonly TestInteropEmployeeId defaultInstance = new TestInteropEmployeeId().MakeReadOnly();
     public static TestInteropEmployeeId DefaultInstance {
       get { return defaultInstance; }
     }
     
     public override TestInteropEmployeeId DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestInteropEmployeeId ThisMessage {
@@ -1077,6 +1089,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestInteropEmployeeId ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestInteropEmployeeId MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -1092,22 +1108,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestInteropEmployeeId();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestInteropEmployeeId cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestInteropEmployeeId result;
+      private bool resultIsReadOnly;
+      private TestInteropEmployeeId result;
       
       private TestInteropEmployeeId PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestInteropEmployeeId original = result;
           result = new TestInteropEmployeeId();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -1122,13 +1138,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestInteropEmployeeId();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -1144,11 +1160,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestInteropEmployeeId BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       
@@ -1182,13 +1198,13 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestMissingFieldsA : pb::GeneratedMessage<TestMissingFieldsA, TestMissingFieldsA.Builder> {
-    private static readonly TestMissingFieldsA defaultInstance = new Builder().BuildPartial();
+    private static readonly TestMissingFieldsA defaultInstance = new TestMissingFieldsA().MakeReadOnly();
     public static TestMissingFieldsA DefaultInstance {
       get { return defaultInstance; }
     }
     
     public override TestMissingFieldsA DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestMissingFieldsA ThisMessage {
@@ -1212,13 +1228,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class SubA : pb::GeneratedMessage<SubA, SubA.Builder> {
-        private static readonly SubA defaultInstance = new Builder().BuildPartial();
+        private static readonly SubA defaultInstance = new SubA().MakeReadOnly();
         public static SubA DefaultInstance {
           get { return defaultInstance; }
         }
         
         public override SubA DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override SubA ThisMessage {
@@ -1285,6 +1301,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static SubA ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private SubA MakeReadOnly() {
+          values_.MakeReadOnly();
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -1300,22 +1321,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new SubA();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(SubA cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          SubA result;
+          private bool resultIsReadOnly;
+          private SubA result;
           
           private SubA PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               SubA original = result;
               result = new SubA();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -1330,13 +1351,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new SubA();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -1352,12 +1373,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override SubA BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            result.values_.MakeReadOnly();
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           
@@ -1453,12 +1473,12 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     public const int TestAFieldNumber = 11;
     private bool hasTestA;
-    private global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsA.Types.SubA testA_ = global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsA.Types.SubA.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsA.Types.SubA testA_;
     public bool HasTestA {
       get { return hasTestA; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsA.Types.SubA TestA {
-      get { return testA_; }
+      get { return testA_ ?? global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsA.Types.SubA.DefaultInstance; }
     }
     
     public static TestMissingFieldsA ParseFrom(pb::ByteString data) {
@@ -1491,6 +1511,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestMissingFieldsA ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestMissingFieldsA MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -1506,22 +1530,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestMissingFieldsA();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestMissingFieldsA cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestMissingFieldsA result;
+      private bool resultIsReadOnly;
+      private TestMissingFieldsA result;
       
       private TestMissingFieldsA PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestMissingFieldsA original = result;
           result = new TestMissingFieldsA();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -1536,13 +1560,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestMissingFieldsA();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -1558,11 +1582,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestMissingFieldsA BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       
@@ -1664,7 +1688,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearTestA() {
         PrepareBuilder();
         result.hasTestA = false;
-        result.testA_ = global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsA.Types.SubA.DefaultInstance;
+        result.testA_ = null;
         return this;
       }
     }
@@ -1677,13 +1701,13 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestMissingFieldsB : pb::GeneratedMessage<TestMissingFieldsB, TestMissingFieldsB.Builder> {
-    private static readonly TestMissingFieldsB defaultInstance = new Builder().BuildPartial();
+    private static readonly TestMissingFieldsB defaultInstance = new TestMissingFieldsB().MakeReadOnly();
     public static TestMissingFieldsB DefaultInstance {
       get { return defaultInstance; }
     }
     
     public override TestMissingFieldsB DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestMissingFieldsB ThisMessage {
@@ -1707,13 +1731,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class SubB : pb::GeneratedMessage<SubB, SubB.Builder> {
-        private static readonly SubB defaultInstance = new Builder().BuildPartial();
+        private static readonly SubB defaultInstance = new SubB().MakeReadOnly();
         public static SubB DefaultInstance {
           get { return defaultInstance; }
         }
         
         public override SubB DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override SubB ThisMessage {
@@ -1770,6 +1794,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static SubB ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private SubB MakeReadOnly() {
+          values_.MakeReadOnly();
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -1785,22 +1814,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new SubB();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(SubB cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          SubB result;
+          private bool resultIsReadOnly;
+          private SubB result;
           
           private SubB PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               SubB original = result;
               result = new SubB();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -1815,13 +1844,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new SubB();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -1837,12 +1866,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override SubB BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            result.values_.MakeReadOnly();
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           
@@ -1918,12 +1946,12 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     public const int TestBFieldNumber = 12;
     private bool hasTestB;
-    private global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsB.Types.SubB testB_ = global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsB.Types.SubB.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsB.Types.SubB testB_;
     public bool HasTestB {
       get { return hasTestB; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsB.Types.SubB TestB {
-      get { return testB_; }
+      get { return testB_ ?? global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsB.Types.SubB.DefaultInstance; }
     }
     
     public static TestMissingFieldsB ParseFrom(pb::ByteString data) {
@@ -1956,6 +1984,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestMissingFieldsB ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestMissingFieldsB MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -1971,22 +2003,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestMissingFieldsB();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestMissingFieldsB cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestMissingFieldsB result;
+      private bool resultIsReadOnly;
+      private TestMissingFieldsB result;
       
       private TestMissingFieldsB PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestMissingFieldsB original = result;
           result = new TestMissingFieldsB();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -2001,13 +2033,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestMissingFieldsB();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -2023,11 +2055,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestMissingFieldsB BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       
@@ -2129,7 +2161,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearTestB() {
         PrepareBuilder();
         result.hasTestB = false;
-        result.testB_ = global::Google.ProtocolBuffers.TestProtos.TestMissingFieldsB.Types.SubB.DefaultInstance;
+        result.testB_ = null;
         return this;
       }
     }
diff --git a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasLiteProtoFile.cs b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasLiteProtoFile.cs
index cbbc50db..d070aedc 100644
--- a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasLiteProtoFile.cs
+++ b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestExtrasLiteProtoFile.cs
@@ -59,7 +59,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestRequiredLite : pb::GeneratedMessageLite<TestRequiredLite, TestRequiredLite.Builder> {
-    private static readonly TestRequiredLite defaultInstance = new Builder().BuildPartial();
+    private static readonly TestRequiredLite defaultInstance = new TestRequiredLite().MakeReadOnly();
     private static readonly string[] _testRequiredLiteFieldNames = new string[] { "d", "en" };
     private static readonly uint[] _testRequiredLiteFieldTags = new uint[] { 8, 16 };
     public static TestRequiredLite DefaultInstance {
@@ -67,7 +67,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestRequiredLite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestRequiredLite ThisMessage {
@@ -183,6 +183,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestRequiredLite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestRequiredLite MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -198,22 +202,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestRequiredLite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestRequiredLite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestRequiredLite result;
+      private bool resultIsReadOnly;
+      private TestRequiredLite result;
       
       private TestRequiredLite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestRequiredLite original = result;
           result = new TestRequiredLite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -228,13 +232,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestRequiredLite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -246,11 +250,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestRequiredLite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
@@ -371,7 +375,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestInteropPersonLite : pb::ExtendableMessageLite<TestInteropPersonLite, TestInteropPersonLite.Builder> {
-    private static readonly TestInteropPersonLite defaultInstance = new Builder().BuildPartial();
+    private static readonly TestInteropPersonLite defaultInstance = new TestInteropPersonLite().MakeReadOnly();
     private static readonly string[] _testInteropPersonLiteFieldNames = new string[] { "addresses", "codes", "email", "id", "name", "phone" };
     private static readonly uint[] _testInteropPersonLiteFieldTags = new uint[] { 43, 82, 26, 16, 10, 34 };
     public static TestInteropPersonLite DefaultInstance {
@@ -379,7 +383,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestInteropPersonLite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestInteropPersonLite ThisMessage {
@@ -403,7 +407,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class PhoneNumber : pb::GeneratedMessageLite<PhoneNumber, PhoneNumber.Builder> {
-        private static readonly PhoneNumber defaultInstance = new Builder().BuildPartial();
+        private static readonly PhoneNumber defaultInstance = new PhoneNumber().MakeReadOnly();
         private static readonly string[] _phoneNumberFieldNames = new string[] { "number", "type" };
         private static readonly uint[] _phoneNumberFieldTags = new uint[] { 10, 16 };
         public static PhoneNumber DefaultInstance {
@@ -411,7 +415,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public override PhoneNumber DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override PhoneNumber ThisMessage {
@@ -526,6 +530,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static PhoneNumber ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private PhoneNumber MakeReadOnly() {
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -541,22 +549,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new PhoneNumber();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(PhoneNumber cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          PhoneNumber result;
+          private bool resultIsReadOnly;
+          private PhoneNumber result;
           
           private PhoneNumber PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               PhoneNumber original = result;
               result = new PhoneNumber();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -571,13 +579,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new PhoneNumber();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -589,11 +597,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override PhoneNumber BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           public override Builder MergeFrom(pb::IMessageLite other) {
@@ -715,7 +723,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class Addresses : pb::GeneratedMessageLite<Addresses, Addresses.Builder> {
-        private static readonly Addresses defaultInstance = new Builder().BuildPartial();
+        private static readonly Addresses defaultInstance = new Addresses().MakeReadOnly();
         private static readonly string[] _addressesFieldNames = new string[] { "address", "address2", "city", "state", "zip" };
         private static readonly uint[] _addressesFieldTags = new uint[] { 10, 18, 26, 34, 45 };
         public static Addresses DefaultInstance {
@@ -723,7 +731,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public override Addresses DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override Addresses ThisMessage {
@@ -899,6 +907,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static Addresses ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private Addresses MakeReadOnly() {
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -914,22 +926,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new Addresses();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(Addresses cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          Addresses result;
+          private bool resultIsReadOnly;
+          private Addresses result;
           
           private Addresses PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               Addresses original = result;
               result = new Addresses();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -944,13 +956,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new Addresses();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -962,11 +974,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Addresses BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           public override Builder MergeFrom(pb::IMessageLite other) {
@@ -1388,6 +1400,13 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestInteropPersonLite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestInteropPersonLite MakeReadOnly() {
+      codes_.MakeReadOnly();
+      phone_.MakeReadOnly();
+      addresses_.MakeReadOnly();
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -1403,22 +1422,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestInteropPersonLite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestInteropPersonLite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestInteropPersonLite result;
+      private bool resultIsReadOnly;
+      private TestInteropPersonLite result;
       
       private TestInteropPersonLite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestInteropPersonLite original = result;
           result = new TestInteropPersonLite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -1433,13 +1452,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestInteropPersonLite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -1451,14 +1470,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestInteropPersonLite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        result.codes_.MakeReadOnly();
-        result.phone_.MakeReadOnly();
-        result.addresses_.MakeReadOnly();
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
@@ -1745,7 +1761,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestInteropEmployeeIdLite : pb::GeneratedMessageLite<TestInteropEmployeeIdLite, TestInteropEmployeeIdLite.Builder> {
-    private static readonly TestInteropEmployeeIdLite defaultInstance = new Builder().BuildPartial();
+    private static readonly TestInteropEmployeeIdLite defaultInstance = new TestInteropEmployeeIdLite().MakeReadOnly();
     private static readonly string[] _testInteropEmployeeIdLiteFieldNames = new string[] { "number" };
     private static readonly uint[] _testInteropEmployeeIdLiteFieldTags = new uint[] { 10 };
     public static TestInteropEmployeeIdLite DefaultInstance {
@@ -1753,7 +1769,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestInteropEmployeeIdLite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestInteropEmployeeIdLite ThisMessage {
@@ -1849,6 +1865,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestInteropEmployeeIdLite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestInteropEmployeeIdLite MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -1864,22 +1884,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestInteropEmployeeIdLite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestInteropEmployeeIdLite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestInteropEmployeeIdLite result;
+      private bool resultIsReadOnly;
+      private TestInteropEmployeeIdLite result;
       
       private TestInteropEmployeeIdLite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestInteropEmployeeIdLite original = result;
           result = new TestInteropEmployeeIdLite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -1894,13 +1914,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestInteropEmployeeIdLite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -1912,11 +1932,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestInteropEmployeeIdLite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
diff --git a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportLiteProtoFile.cs b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportLiteProtoFile.cs
index 0df40f42..3eb3062c 100644
--- a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportLiteProtoFile.cs
+++ b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportLiteProtoFile.cs
@@ -43,7 +43,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class ImportMessageLite : pb::GeneratedMessageLite<ImportMessageLite, ImportMessageLite.Builder> {
-    private static readonly ImportMessageLite defaultInstance = new Builder().BuildPartial();
+    private static readonly ImportMessageLite defaultInstance = new ImportMessageLite().MakeReadOnly();
     private static readonly string[] _importMessageLiteFieldNames = new string[] { "d" };
     private static readonly uint[] _importMessageLiteFieldTags = new uint[] { 8 };
     public static ImportMessageLite DefaultInstance {
@@ -51,7 +51,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override ImportMessageLite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override ImportMessageLite ThisMessage {
@@ -146,6 +146,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static ImportMessageLite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private ImportMessageLite MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -161,22 +165,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new ImportMessageLite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(ImportMessageLite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      ImportMessageLite result;
+      private bool resultIsReadOnly;
+      private ImportMessageLite result;
       
       private ImportMessageLite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           ImportMessageLite original = result;
           result = new ImportMessageLite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -191,13 +195,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new ImportMessageLite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -209,11 +213,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override ImportMessageLite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
diff --git a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportProtoFile.cs b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportProtoFile.cs
index 75e746a8..6f7f59d5 100644
--- a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportProtoFile.cs
+++ b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestImportProtoFile.cs
@@ -71,7 +71,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class ImportMessage : pb::GeneratedMessage<ImportMessage, ImportMessage.Builder> {
-    private static readonly ImportMessage defaultInstance = new Builder().BuildPartial();
+    private static readonly ImportMessage defaultInstance = new ImportMessage().MakeReadOnly();
     private static readonly string[] _importMessageFieldNames = new string[] { "d" };
     private static readonly uint[] _importMessageFieldTags = new uint[] { 8 };
     public static ImportMessage DefaultInstance {
@@ -79,7 +79,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override ImportMessage DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override ImportMessage ThisMessage {
@@ -165,6 +165,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static ImportMessage ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private ImportMessage MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -180,22 +184,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new ImportMessage();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(ImportMessage cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      ImportMessage result;
+      private bool resultIsReadOnly;
+      private ImportMessage result;
       
       private ImportMessage PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           ImportMessage original = result;
           result = new ImportMessage();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -210,13 +214,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new ImportMessage();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -232,11 +236,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override ImportMessage BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
diff --git a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteImportNonLiteProtoFile.cs b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteImportNonLiteProtoFile.cs
index 5a6033a1..34ae37f9 100644
--- a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteImportNonLiteProtoFile.cs
+++ b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteImportNonLiteProtoFile.cs
@@ -32,7 +32,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestLiteImportsNonlite : pb::GeneratedMessageLite<TestLiteImportsNonlite, TestLiteImportsNonlite.Builder> {
-    private static readonly TestLiteImportsNonlite defaultInstance = new Builder().BuildPartial();
+    private static readonly TestLiteImportsNonlite defaultInstance = new TestLiteImportsNonlite().MakeReadOnly();
     private static readonly string[] _testLiteImportsNonliteFieldNames = new string[] { "message" };
     private static readonly uint[] _testLiteImportsNonliteFieldTags = new uint[] { 10 };
     public static TestLiteImportsNonlite DefaultInstance {
@@ -40,7 +40,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestLiteImportsNonlite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestLiteImportsNonlite ThisMessage {
@@ -49,12 +49,12 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     public const int MessageFieldNumber = 1;
     private bool hasMessage;
-    private global::Google.ProtocolBuffers.TestProtos.TestAllTypes message_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestAllTypes message_;
     public bool HasMessage {
       get { return hasMessage; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestAllTypes Message {
-      get { return message_; }
+      get { return message_ ?? global::Google.ProtocolBuffers.TestProtos.TestAllTypes.DefaultInstance; }
     }
     
     public override bool IsInitialized {
@@ -135,6 +135,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestLiteImportsNonlite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestLiteImportsNonlite MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -150,22 +154,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestLiteImportsNonlite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestLiteImportsNonlite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestLiteImportsNonlite result;
+      private bool resultIsReadOnly;
+      private TestLiteImportsNonlite result;
       
       private TestLiteImportsNonlite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestLiteImportsNonlite original = result;
           result = new TestLiteImportsNonlite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -180,13 +184,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestLiteImportsNonlite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -198,11 +202,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestLiteImportsNonlite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
@@ -304,7 +308,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearMessage() {
         PrepareBuilder();
         result.hasMessage = false;
-        result.message_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.DefaultInstance;
+        result.message_ = null;
         return this;
       }
     }
diff --git a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteProtoFile.cs b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteProtoFile.cs
index 2592c833..5ad75588 100644
--- a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteProtoFile.cs
+++ b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestLiteProtoFile.cs
@@ -1228,7 +1228,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestAllTypesLite : pb::GeneratedMessageLite<TestAllTypesLite, TestAllTypesLite.Builder> {
-    private static readonly TestAllTypesLite defaultInstance = new Builder().BuildPartial();
+    private static readonly TestAllTypesLite defaultInstance = new TestAllTypesLite().MakeReadOnly();
     private static readonly string[] _testAllTypesLiteFieldNames = new string[] { "default_bool", "default_bytes", "default_cord", "default_double", "default_fixed32", "default_fixed64", "default_float", "default_foreign_enum", "default_import_enum", "default_int32", "default_int64", "default_nested_enum", "default_sfixed32", "default_sfixed64", "default_sint32", "default_sint64", "default_string", "default_string_piece", "default_uint32", "default_uint64", "optional_bool", "optional_bytes", "optional_cord", "optional_double", "optional_fixed32", "optional_fixed64", "optional_float", "optional_foreign_enum", "optional_foreign_message", "optional_import_enum", "optional_import_message", "optional_int32", "optional_int64", "optional_nested_enum", "optional_nested_message", "optional_sfixed32", "optional_sfixed64", "optional_sint32", "optional_sint64", "optional_string", "optional_string_piece", "optional_uint32", "optional_uint64", "optionalgroup", "repeated_bool", "repeated_bytes", "repeated_cord", "repeated_double", "repeated_fixed32", "repeated_fixed64", "repeated_float", "repeated_foreign_enum", "repeated_foreign_message", "repeated_import_enum", "repeated_import_message", "repeated_int32", "repeated_int64", "repeated_nested_enum", "repeated_nested_message", "repeated_sfixed32", "repeated_sfixed64", "repeated_sint32", "repeated_sint64", "repeated_string", "repeated_string_piece", "repeated_uint32", "repeated_uint64", "repeatedgroup" };
     private static readonly uint[] _testAllTypesLiteFieldTags = new uint[] { 584, 602, 682, 577, 541, 545, 573, 656, 664, 488, 496, 648, 557, 561, 520, 528, 594, 674, 504, 512, 104, 122, 202, 97, 61, 65, 93, 176, 154, 184, 162, 8, 16, 168, 146, 77, 81, 40, 48, 114, 194, 24, 32, 131, 344, 362, 442, 337, 301, 305, 333, 416, 394, 424, 402, 248, 256, 408, 386, 317, 321, 280, 288, 354, 434, 264, 272, 371 };
     public static TestAllTypesLite DefaultInstance {
@@ -1236,7 +1236,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestAllTypesLite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestAllTypesLite ThisMessage {
@@ -1260,7 +1260,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class NestedMessage : pb::GeneratedMessageLite<NestedMessage, NestedMessage.Builder> {
-        private static readonly NestedMessage defaultInstance = new Builder().BuildPartial();
+        private static readonly NestedMessage defaultInstance = new NestedMessage().MakeReadOnly();
         private static readonly string[] _nestedMessageFieldNames = new string[] { "bb" };
         private static readonly uint[] _nestedMessageFieldTags = new uint[] { 8 };
         public static NestedMessage DefaultInstance {
@@ -1268,7 +1268,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public override NestedMessage DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override NestedMessage ThisMessage {
@@ -1363,6 +1363,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static NestedMessage ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private NestedMessage MakeReadOnly() {
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -1378,22 +1382,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new NestedMessage();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(NestedMessage cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          NestedMessage result;
+          private bool resultIsReadOnly;
+          private NestedMessage result;
           
           private NestedMessage PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               NestedMessage original = result;
               result = new NestedMessage();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -1408,13 +1412,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new NestedMessage();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -1426,11 +1430,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override NestedMessage BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           public override Builder MergeFrom(pb::IMessageLite other) {
@@ -1520,7 +1524,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class OptionalGroup : pb::GeneratedMessageLite<OptionalGroup, OptionalGroup.Builder> {
-        private static readonly OptionalGroup defaultInstance = new Builder().BuildPartial();
+        private static readonly OptionalGroup defaultInstance = new OptionalGroup().MakeReadOnly();
         private static readonly string[] _optionalGroupFieldNames = new string[] { "a" };
         private static readonly uint[] _optionalGroupFieldTags = new uint[] { 136 };
         public static OptionalGroup DefaultInstance {
@@ -1528,7 +1532,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public override OptionalGroup DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override OptionalGroup ThisMessage {
@@ -1623,6 +1627,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static OptionalGroup ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private OptionalGroup MakeReadOnly() {
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -1638,22 +1646,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new OptionalGroup();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(OptionalGroup cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          OptionalGroup result;
+          private bool resultIsReadOnly;
+          private OptionalGroup result;
           
           private OptionalGroup PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               OptionalGroup original = result;
               result = new OptionalGroup();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -1668,13 +1676,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new OptionalGroup();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -1686,11 +1694,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override OptionalGroup BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           public override Builder MergeFrom(pb::IMessageLite other) {
@@ -1780,7 +1788,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class RepeatedGroup : pb::GeneratedMessageLite<RepeatedGroup, RepeatedGroup.Builder> {
-        private static readonly RepeatedGroup defaultInstance = new Builder().BuildPartial();
+        private static readonly RepeatedGroup defaultInstance = new RepeatedGroup().MakeReadOnly();
         private static readonly string[] _repeatedGroupFieldNames = new string[] { "a" };
         private static readonly uint[] _repeatedGroupFieldTags = new uint[] { 376 };
         public static RepeatedGroup DefaultInstance {
@@ -1788,7 +1796,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public override RepeatedGroup DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override RepeatedGroup ThisMessage {
@@ -1883,6 +1891,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static RepeatedGroup ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private RepeatedGroup MakeReadOnly() {
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -1898,22 +1910,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new RepeatedGroup();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(RepeatedGroup cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          RepeatedGroup result;
+          private bool resultIsReadOnly;
+          private RepeatedGroup result;
           
           private RepeatedGroup PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               RepeatedGroup original = result;
               result = new RepeatedGroup();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -1928,13 +1940,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new RepeatedGroup();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -1946,11 +1958,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override RepeatedGroup BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           public override Builder MergeFrom(pb::IMessageLite other) {
@@ -2195,42 +2207,42 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     public const int OptionalGroupFieldNumber = 16;
     private bool hasOptionalGroup;
-    private global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.OptionalGroup optionalGroup_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.OptionalGroup.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.OptionalGroup optionalGroup_;
     public bool HasOptionalGroup {
       get { return hasOptionalGroup; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.OptionalGroup OptionalGroup {
-      get { return optionalGroup_; }
+      get { return optionalGroup_ ?? global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.OptionalGroup.DefaultInstance; }
     }
     
     public const int OptionalNestedMessageFieldNumber = 18;
     private bool hasOptionalNestedMessage;
-    private global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage optionalNestedMessage_;
     public bool HasOptionalNestedMessage {
       get { return hasOptionalNestedMessage; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage OptionalNestedMessage {
-      get { return optionalNestedMessage_; }
+      get { return optionalNestedMessage_ ?? global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage.DefaultInstance; }
     }
     
     public const int OptionalForeignMessageFieldNumber = 19;
     private bool hasOptionalForeignMessage;
-    private global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite optionalForeignMessage_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite optionalForeignMessage_;
     public bool HasOptionalForeignMessage {
       get { return hasOptionalForeignMessage; }
     }
     public global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite OptionalForeignMessage {
-      get { return optionalForeignMessage_; }
+      get { return optionalForeignMessage_ ?? global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite.DefaultInstance; }
     }
     
     public const int OptionalImportMessageFieldNumber = 20;
     private bool hasOptionalImportMessage;
-    private global::Google.ProtocolBuffers.TestProtos.ImportMessageLite optionalImportMessage_ = global::Google.ProtocolBuffers.TestProtos.ImportMessageLite.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.ImportMessageLite optionalImportMessage_;
     public bool HasOptionalImportMessage {
       get { return hasOptionalImportMessage; }
     }
     public global::Google.ProtocolBuffers.TestProtos.ImportMessageLite OptionalImportMessage {
-      get { return optionalImportMessage_; }
+      get { return optionalImportMessage_ ?? global::Google.ProtocolBuffers.TestProtos.ImportMessageLite.DefaultInstance; }
     }
     
     public const int OptionalNestedEnumFieldNumber = 21;
@@ -3628,6 +3640,34 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestAllTypesLite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestAllTypesLite MakeReadOnly() {
+      repeatedInt32_.MakeReadOnly();
+      repeatedInt64_.MakeReadOnly();
+      repeatedUint32_.MakeReadOnly();
+      repeatedUint64_.MakeReadOnly();
+      repeatedSint32_.MakeReadOnly();
+      repeatedSint64_.MakeReadOnly();
+      repeatedFixed32_.MakeReadOnly();
+      repeatedFixed64_.MakeReadOnly();
+      repeatedSfixed32_.MakeReadOnly();
+      repeatedSfixed64_.MakeReadOnly();
+      repeatedFloat_.MakeReadOnly();
+      repeatedDouble_.MakeReadOnly();
+      repeatedBool_.MakeReadOnly();
+      repeatedString_.MakeReadOnly();
+      repeatedBytes_.MakeReadOnly();
+      repeatedGroup_.MakeReadOnly();
+      repeatedNestedMessage_.MakeReadOnly();
+      repeatedForeignMessage_.MakeReadOnly();
+      repeatedImportMessage_.MakeReadOnly();
+      repeatedNestedEnum_.MakeReadOnly();
+      repeatedForeignEnum_.MakeReadOnly();
+      repeatedImportEnum_.MakeReadOnly();
+      repeatedStringPiece_.MakeReadOnly();
+      repeatedCord_.MakeReadOnly();
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -3643,22 +3683,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestAllTypesLite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestAllTypesLite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestAllTypesLite result;
+      private bool resultIsReadOnly;
+      private TestAllTypesLite result;
       
       private TestAllTypesLite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestAllTypesLite original = result;
           result = new TestAllTypesLite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -3673,13 +3713,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestAllTypesLite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -3691,35 +3731,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestAllTypesLite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        result.repeatedInt32_.MakeReadOnly();
-        result.repeatedInt64_.MakeReadOnly();
-        result.repeatedUint32_.MakeReadOnly();
-        result.repeatedUint64_.MakeReadOnly();
-        result.repeatedSint32_.MakeReadOnly();
-        result.repeatedSint64_.MakeReadOnly();
-        result.repeatedFixed32_.MakeReadOnly();
-        result.repeatedFixed64_.MakeReadOnly();
-        result.repeatedSfixed32_.MakeReadOnly();
-        result.repeatedSfixed64_.MakeReadOnly();
-        result.repeatedFloat_.MakeReadOnly();
-        result.repeatedDouble_.MakeReadOnly();
-        result.repeatedBool_.MakeReadOnly();
-        result.repeatedString_.MakeReadOnly();
-        result.repeatedBytes_.MakeReadOnly();
-        result.repeatedGroup_.MakeReadOnly();
-        result.repeatedNestedMessage_.MakeReadOnly();
-        result.repeatedForeignMessage_.MakeReadOnly();
-        result.repeatedImportMessage_.MakeReadOnly();
-        result.repeatedNestedEnum_.MakeReadOnly();
-        result.repeatedForeignEnum_.MakeReadOnly();
-        result.repeatedImportEnum_.MakeReadOnly();
-        result.repeatedStringPiece_.MakeReadOnly();
-        result.repeatedCord_.MakeReadOnly();
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
@@ -4658,7 +4674,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearOptionalGroup() {
         PrepareBuilder();
         result.hasOptionalGroup = false;
-        result.optionalGroup_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.OptionalGroup.DefaultInstance;
+        result.optionalGroup_ = null;
         return this;
       }
       
@@ -4698,7 +4714,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearOptionalNestedMessage() {
         PrepareBuilder();
         result.hasOptionalNestedMessage = false;
-        result.optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypesLite.Types.NestedMessage.DefaultInstance;
+        result.optionalNestedMessage_ = null;
         return this;
       }
       
@@ -4738,7 +4754,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearOptionalForeignMessage() {
         PrepareBuilder();
         result.hasOptionalForeignMessage = false;
-        result.optionalForeignMessage_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessageLite.DefaultInstance;
+        result.optionalForeignMessage_ = null;
         return this;
       }
       
@@ -4778,7 +4794,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearOptionalImportMessage() {
         PrepareBuilder();
         result.hasOptionalImportMessage = false;
-        result.optionalImportMessage_ = global::Google.ProtocolBuffers.TestProtos.ImportMessageLite.DefaultInstance;
+        result.optionalImportMessage_ = null;
         return this;
       }
       
@@ -6109,7 +6125,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class ForeignMessageLite : pb::GeneratedMessageLite<ForeignMessageLite, ForeignMessageLite.Builder> {
-    private static readonly ForeignMessageLite defaultInstance = new Builder().BuildPartial();
+    private static readonly ForeignMessageLite defaultInstance = new ForeignMessageLite().MakeReadOnly();
     private static readonly string[] _foreignMessageLiteFieldNames = new string[] { "c" };
     private static readonly uint[] _foreignMessageLiteFieldTags = new uint[] { 8 };
     public static ForeignMessageLite DefaultInstance {
@@ -6117,7 +6133,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override ForeignMessageLite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override ForeignMessageLite ThisMessage {
@@ -6212,6 +6228,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static ForeignMessageLite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private ForeignMessageLite MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -6227,22 +6247,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new ForeignMessageLite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(ForeignMessageLite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      ForeignMessageLite result;
+      private bool resultIsReadOnly;
+      private ForeignMessageLite result;
       
       private ForeignMessageLite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           ForeignMessageLite original = result;
           result = new ForeignMessageLite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -6257,13 +6277,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new ForeignMessageLite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -6275,11 +6295,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override ForeignMessageLite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
@@ -6369,7 +6389,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestPackedTypesLite : pb::GeneratedMessageLite<TestPackedTypesLite, TestPackedTypesLite.Builder> {
-    private static readonly TestPackedTypesLite defaultInstance = new Builder().BuildPartial();
+    private static readonly TestPackedTypesLite defaultInstance = new TestPackedTypesLite().MakeReadOnly();
     private static readonly string[] _testPackedTypesLiteFieldNames = new string[] { "packed_bool", "packed_double", "packed_enum", "packed_fixed32", "packed_fixed64", "packed_float", "packed_int32", "packed_int64", "packed_sfixed32", "packed_sfixed64", "packed_sint32", "packed_sint64", "packed_uint32", "packed_uint64" };
     private static readonly uint[] _testPackedTypesLiteFieldTags = new uint[] { 818, 810, 826, 770, 778, 802, 722, 730, 786, 794, 754, 762, 738, 746 };
     public static TestPackedTypesLite DefaultInstance {
@@ -6377,7 +6397,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestPackedTypesLite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestPackedTypesLite ThisMessage {
@@ -6910,6 +6930,24 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestPackedTypesLite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestPackedTypesLite MakeReadOnly() {
+      packedInt32_.MakeReadOnly();
+      packedInt64_.MakeReadOnly();
+      packedUint32_.MakeReadOnly();
+      packedUint64_.MakeReadOnly();
+      packedSint32_.MakeReadOnly();
+      packedSint64_.MakeReadOnly();
+      packedFixed32_.MakeReadOnly();
+      packedFixed64_.MakeReadOnly();
+      packedSfixed32_.MakeReadOnly();
+      packedSfixed64_.MakeReadOnly();
+      packedFloat_.MakeReadOnly();
+      packedDouble_.MakeReadOnly();
+      packedBool_.MakeReadOnly();
+      packedEnum_.MakeReadOnly();
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -6925,22 +6963,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestPackedTypesLite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestPackedTypesLite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestPackedTypesLite result;
+      private bool resultIsReadOnly;
+      private TestPackedTypesLite result;
       
       private TestPackedTypesLite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestPackedTypesLite original = result;
           result = new TestPackedTypesLite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -6955,13 +6993,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestPackedTypesLite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -6973,25 +7011,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestPackedTypesLite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        result.packedInt32_.MakeReadOnly();
-        result.packedInt64_.MakeReadOnly();
-        result.packedUint32_.MakeReadOnly();
-        result.packedUint64_.MakeReadOnly();
-        result.packedSint32_.MakeReadOnly();
-        result.packedSint64_.MakeReadOnly();
-        result.packedFixed32_.MakeReadOnly();
-        result.packedFixed64_.MakeReadOnly();
-        result.packedSfixed32_.MakeReadOnly();
-        result.packedSfixed64_.MakeReadOnly();
-        result.packedFloat_.MakeReadOnly();
-        result.packedDouble_.MakeReadOnly();
-        result.packedBool_.MakeReadOnly();
-        result.packedEnum_.MakeReadOnly();
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
@@ -7607,7 +7631,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestUnpackedTypesLite : pb::GeneratedMessageLite<TestUnpackedTypesLite, TestUnpackedTypesLite.Builder> {
-    private static readonly TestUnpackedTypesLite defaultInstance = new Builder().BuildPartial();
+    private static readonly TestUnpackedTypesLite defaultInstance = new TestUnpackedTypesLite().MakeReadOnly();
     private static readonly string[] _testUnpackedTypesLiteFieldNames = new string[] { "unpacked_bool", "unpacked_double", "unpacked_enum", "unpacked_fixed32", "unpacked_fixed64", "unpacked_float", "unpacked_int32", "unpacked_int64", "unpacked_sfixed32", "unpacked_sfixed64", "unpacked_sint32", "unpacked_sint64", "unpacked_uint32", "unpacked_uint64" };
     private static readonly uint[] _testUnpackedTypesLiteFieldTags = new uint[] { 816, 809, 824, 773, 777, 805, 720, 728, 789, 793, 752, 760, 736, 744 };
     public static TestUnpackedTypesLite DefaultInstance {
@@ -7615,7 +7639,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestUnpackedTypesLite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestUnpackedTypesLite ThisMessage {
@@ -8093,6 +8117,24 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestUnpackedTypesLite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestUnpackedTypesLite MakeReadOnly() {
+      unpackedInt32_.MakeReadOnly();
+      unpackedInt64_.MakeReadOnly();
+      unpackedUint32_.MakeReadOnly();
+      unpackedUint64_.MakeReadOnly();
+      unpackedSint32_.MakeReadOnly();
+      unpackedSint64_.MakeReadOnly();
+      unpackedFixed32_.MakeReadOnly();
+      unpackedFixed64_.MakeReadOnly();
+      unpackedSfixed32_.MakeReadOnly();
+      unpackedSfixed64_.MakeReadOnly();
+      unpackedFloat_.MakeReadOnly();
+      unpackedDouble_.MakeReadOnly();
+      unpackedBool_.MakeReadOnly();
+      unpackedEnum_.MakeReadOnly();
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -8108,22 +8150,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestUnpackedTypesLite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestUnpackedTypesLite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestUnpackedTypesLite result;
+      private bool resultIsReadOnly;
+      private TestUnpackedTypesLite result;
       
       private TestUnpackedTypesLite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestUnpackedTypesLite original = result;
           result = new TestUnpackedTypesLite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -8138,13 +8180,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestUnpackedTypesLite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -8156,25 +8198,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestUnpackedTypesLite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        result.unpackedInt32_.MakeReadOnly();
-        result.unpackedInt64_.MakeReadOnly();
-        result.unpackedUint32_.MakeReadOnly();
-        result.unpackedUint64_.MakeReadOnly();
-        result.unpackedSint32_.MakeReadOnly();
-        result.unpackedSint64_.MakeReadOnly();
-        result.unpackedFixed32_.MakeReadOnly();
-        result.unpackedFixed64_.MakeReadOnly();
-        result.unpackedSfixed32_.MakeReadOnly();
-        result.unpackedSfixed64_.MakeReadOnly();
-        result.unpackedFloat_.MakeReadOnly();
-        result.unpackedDouble_.MakeReadOnly();
-        result.unpackedBool_.MakeReadOnly();
-        result.unpackedEnum_.MakeReadOnly();
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
@@ -8790,7 +8818,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestAllExtensionsLite : pb::ExtendableMessageLite<TestAllExtensionsLite, TestAllExtensionsLite.Builder> {
-    private static readonly TestAllExtensionsLite defaultInstance = new Builder().BuildPartial();
+    private static readonly TestAllExtensionsLite defaultInstance = new TestAllExtensionsLite().MakeReadOnly();
     private static readonly string[] _testAllExtensionsLiteFieldNames = new string[] {  };
     private static readonly uint[] _testAllExtensionsLiteFieldTags = new uint[] {  };
     public static TestAllExtensionsLite DefaultInstance {
@@ -8798,7 +8826,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestAllExtensionsLite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestAllExtensionsLite ThisMessage {
@@ -8881,6 +8909,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestAllExtensionsLite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestAllExtensionsLite MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -8896,22 +8928,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestAllExtensionsLite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestAllExtensionsLite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestAllExtensionsLite result;
+      private bool resultIsReadOnly;
+      private TestAllExtensionsLite result;
       
       private TestAllExtensionsLite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestAllExtensionsLite original = result;
           result = new TestAllExtensionsLite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -8926,13 +8958,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestAllExtensionsLite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -8944,11 +8976,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestAllExtensionsLite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
@@ -9012,7 +9044,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class OptionalGroup_extension_lite : pb::GeneratedMessageLite<OptionalGroup_extension_lite, OptionalGroup_extension_lite.Builder> {
-    private static readonly OptionalGroup_extension_lite defaultInstance = new Builder().BuildPartial();
+    private static readonly OptionalGroup_extension_lite defaultInstance = new OptionalGroup_extension_lite().MakeReadOnly();
     private static readonly string[] _optionalGroupExtensionLiteFieldNames = new string[] { "a" };
     private static readonly uint[] _optionalGroupExtensionLiteFieldTags = new uint[] { 136 };
     public static OptionalGroup_extension_lite DefaultInstance {
@@ -9020,7 +9052,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override OptionalGroup_extension_lite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override OptionalGroup_extension_lite ThisMessage {
@@ -9115,6 +9147,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static OptionalGroup_extension_lite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private OptionalGroup_extension_lite MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -9130,22 +9166,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new OptionalGroup_extension_lite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(OptionalGroup_extension_lite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      OptionalGroup_extension_lite result;
+      private bool resultIsReadOnly;
+      private OptionalGroup_extension_lite result;
       
       private OptionalGroup_extension_lite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           OptionalGroup_extension_lite original = result;
           result = new OptionalGroup_extension_lite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -9160,13 +9196,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new OptionalGroup_extension_lite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -9178,11 +9214,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override OptionalGroup_extension_lite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
@@ -9272,7 +9308,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class RepeatedGroup_extension_lite : pb::GeneratedMessageLite<RepeatedGroup_extension_lite, RepeatedGroup_extension_lite.Builder> {
-    private static readonly RepeatedGroup_extension_lite defaultInstance = new Builder().BuildPartial();
+    private static readonly RepeatedGroup_extension_lite defaultInstance = new RepeatedGroup_extension_lite().MakeReadOnly();
     private static readonly string[] _repeatedGroupExtensionLiteFieldNames = new string[] { "a" };
     private static readonly uint[] _repeatedGroupExtensionLiteFieldTags = new uint[] { 376 };
     public static RepeatedGroup_extension_lite DefaultInstance {
@@ -9280,7 +9316,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override RepeatedGroup_extension_lite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override RepeatedGroup_extension_lite ThisMessage {
@@ -9375,6 +9411,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static RepeatedGroup_extension_lite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private RepeatedGroup_extension_lite MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -9390,22 +9430,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new RepeatedGroup_extension_lite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(RepeatedGroup_extension_lite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      RepeatedGroup_extension_lite result;
+      private bool resultIsReadOnly;
+      private RepeatedGroup_extension_lite result;
       
       private RepeatedGroup_extension_lite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           RepeatedGroup_extension_lite original = result;
           result = new RepeatedGroup_extension_lite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -9420,13 +9460,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new RepeatedGroup_extension_lite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -9438,11 +9478,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override RepeatedGroup_extension_lite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
@@ -9532,7 +9572,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestPackedExtensionsLite : pb::ExtendableMessageLite<TestPackedExtensionsLite, TestPackedExtensionsLite.Builder> {
-    private static readonly TestPackedExtensionsLite defaultInstance = new Builder().BuildPartial();
+    private static readonly TestPackedExtensionsLite defaultInstance = new TestPackedExtensionsLite().MakeReadOnly();
     private static readonly string[] _testPackedExtensionsLiteFieldNames = new string[] {  };
     private static readonly uint[] _testPackedExtensionsLiteFieldTags = new uint[] {  };
     public static TestPackedExtensionsLite DefaultInstance {
@@ -9540,7 +9580,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestPackedExtensionsLite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestPackedExtensionsLite ThisMessage {
@@ -9623,6 +9663,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestPackedExtensionsLite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestPackedExtensionsLite MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -9638,22 +9682,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestPackedExtensionsLite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestPackedExtensionsLite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestPackedExtensionsLite result;
+      private bool resultIsReadOnly;
+      private TestPackedExtensionsLite result;
       
       private TestPackedExtensionsLite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestPackedExtensionsLite original = result;
           result = new TestPackedExtensionsLite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -9668,13 +9712,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestPackedExtensionsLite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -9686,11 +9730,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestPackedExtensionsLite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
@@ -9754,7 +9798,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestUnpackedExtensionsLite : pb::ExtendableMessageLite<TestUnpackedExtensionsLite, TestUnpackedExtensionsLite.Builder> {
-    private static readonly TestUnpackedExtensionsLite defaultInstance = new Builder().BuildPartial();
+    private static readonly TestUnpackedExtensionsLite defaultInstance = new TestUnpackedExtensionsLite().MakeReadOnly();
     private static readonly string[] _testUnpackedExtensionsLiteFieldNames = new string[] {  };
     private static readonly uint[] _testUnpackedExtensionsLiteFieldTags = new uint[] {  };
     public static TestUnpackedExtensionsLite DefaultInstance {
@@ -9762,7 +9806,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestUnpackedExtensionsLite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestUnpackedExtensionsLite ThisMessage {
@@ -9845,6 +9889,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestUnpackedExtensionsLite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestUnpackedExtensionsLite MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -9860,22 +9908,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestUnpackedExtensionsLite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestUnpackedExtensionsLite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestUnpackedExtensionsLite result;
+      private bool resultIsReadOnly;
+      private TestUnpackedExtensionsLite result;
       
       private TestUnpackedExtensionsLite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestUnpackedExtensionsLite original = result;
           result = new TestUnpackedExtensionsLite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -9890,13 +9938,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestUnpackedExtensionsLite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -9908,11 +9956,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestUnpackedExtensionsLite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
@@ -9976,7 +10024,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestNestedExtensionLite : pb::GeneratedMessageLite<TestNestedExtensionLite, TestNestedExtensionLite.Builder> {
-    private static readonly TestNestedExtensionLite defaultInstance = new Builder().BuildPartial();
+    private static readonly TestNestedExtensionLite defaultInstance = new TestNestedExtensionLite().MakeReadOnly();
     private static readonly string[] _testNestedExtensionLiteFieldNames = new string[] {  };
     private static readonly uint[] _testNestedExtensionLiteFieldTags = new uint[] {  };
     public static TestNestedExtensionLite DefaultInstance {
@@ -9984,7 +10032,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestNestedExtensionLite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestNestedExtensionLite ThisMessage {
@@ -10062,6 +10110,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestNestedExtensionLite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestNestedExtensionLite MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -10077,22 +10129,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestNestedExtensionLite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestNestedExtensionLite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestNestedExtensionLite result;
+      private bool resultIsReadOnly;
+      private TestNestedExtensionLite result;
       
       private TestNestedExtensionLite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestNestedExtensionLite original = result;
           result = new TestNestedExtensionLite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -10107,13 +10159,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestNestedExtensionLite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -10125,11 +10177,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestNestedExtensionLite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
@@ -10192,7 +10244,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestDeprecatedLite : pb::GeneratedMessageLite<TestDeprecatedLite, TestDeprecatedLite.Builder> {
-    private static readonly TestDeprecatedLite defaultInstance = new Builder().BuildPartial();
+    private static readonly TestDeprecatedLite defaultInstance = new TestDeprecatedLite().MakeReadOnly();
     private static readonly string[] _testDeprecatedLiteFieldNames = new string[] { "deprecated_field" };
     private static readonly uint[] _testDeprecatedLiteFieldTags = new uint[] { 8 };
     public static TestDeprecatedLite DefaultInstance {
@@ -10200,7 +10252,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestDeprecatedLite DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestDeprecatedLite ThisMessage {
@@ -10295,6 +10347,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestDeprecatedLite ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestDeprecatedLite MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -10310,22 +10366,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestDeprecatedLite();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestDeprecatedLite cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestDeprecatedLite result;
+      private bool resultIsReadOnly;
+      private TestDeprecatedLite result;
       
       private TestDeprecatedLite PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestDeprecatedLite original = result;
           result = new TestDeprecatedLite();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -10340,13 +10396,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestDeprecatedLite();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -10358,11 +10414,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestDeprecatedLite BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessageLite other) {
diff --git a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestProtoFile.cs b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestProtoFile.cs
index aeea673d..0c66d4bc 100644
--- a/src/ProtocolBuffersLite.Test/TestProtos/UnitTestProtoFile.cs
+++ b/src/ProtocolBuffersLite.Test/TestProtos/UnitTestProtoFile.cs
@@ -1122,7 +1122,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestAllTypes : pb::GeneratedMessage<TestAllTypes, TestAllTypes.Builder> {
-    private static readonly TestAllTypes defaultInstance = new Builder().BuildPartial();
+    private static readonly TestAllTypes defaultInstance = new TestAllTypes().MakeReadOnly();
     private static readonly string[] _testAllTypesFieldNames = new string[] { "default_bool", "default_bytes", "default_cord", "default_double", "default_fixed32", "default_fixed64", "default_float", "default_foreign_enum", "default_import_enum", "default_int32", "default_int64", "default_nested_enum", "default_sfixed32", "default_sfixed64", "default_sint32", "default_sint64", "default_string", "default_string_piece", "default_uint32", "default_uint64", "optional_bool", "optional_bytes", "optional_cord", "optional_double", "optional_fixed32", "optional_fixed64", "optional_float", "optional_foreign_enum", "optional_foreign_message", "optional_import_enum", "optional_import_message", "optional_int32", "optional_int64", "optional_nested_enum", "optional_nested_message", "optional_sfixed32", "optional_sfixed64", "optional_sint32", "optional_sint64", "optional_string", "optional_string_piece", "optional_uint32", "optional_uint64", "optionalgroup", "repeated_bool", "repeated_bytes", "repeated_cord", "repeated_double", "repeated_fixed32", "repeated_fixed64", "repeated_float", "repeated_foreign_enum", "repeated_foreign_message", "repeated_import_enum", "repeated_import_message", "repeated_int32", "repeated_int64", "repeated_nested_enum", "repeated_nested_message", "repeated_sfixed32", "repeated_sfixed64", "repeated_sint32", "repeated_sint64", "repeated_string", "repeated_string_piece", "repeated_uint32", "repeated_uint64", "repeatedgroup" };
     private static readonly uint[] _testAllTypesFieldTags = new uint[] { 584, 602, 682, 577, 541, 545, 573, 656, 664, 488, 496, 648, 557, 561, 520, 528, 594, 674, 504, 512, 104, 122, 202, 97, 61, 65, 93, 176, 154, 184, 162, 8, 16, 168, 146, 77, 81, 40, 48, 114, 194, 24, 32, 131, 344, 362, 442, 337, 301, 305, 333, 416, 394, 424, 402, 248, 256, 408, 386, 317, 321, 280, 288, 354, 434, 264, 272, 371 };
     public static TestAllTypes DefaultInstance {
@@ -1130,7 +1130,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestAllTypes DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestAllTypes ThisMessage {
@@ -1162,7 +1162,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class NestedMessage : pb::GeneratedMessage<NestedMessage, NestedMessage.Builder> {
-        private static readonly NestedMessage defaultInstance = new Builder().BuildPartial();
+        private static readonly NestedMessage defaultInstance = new NestedMessage().MakeReadOnly();
         private static readonly string[] _nestedMessageFieldNames = new string[] { "bb" };
         private static readonly uint[] _nestedMessageFieldTags = new uint[] { 8 };
         public static NestedMessage DefaultInstance {
@@ -1170,7 +1170,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public override NestedMessage DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override NestedMessage ThisMessage {
@@ -1256,6 +1256,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static NestedMessage ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private NestedMessage MakeReadOnly() {
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -1271,22 +1275,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new NestedMessage();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(NestedMessage cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          NestedMessage result;
+          private bool resultIsReadOnly;
+          private NestedMessage result;
           
           private NestedMessage PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               NestedMessage original = result;
               result = new NestedMessage();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -1301,13 +1305,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new NestedMessage();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -1323,11 +1327,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override NestedMessage BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           public override Builder MergeFrom(pb::IMessage other) {
@@ -1431,7 +1435,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class OptionalGroup : pb::GeneratedMessage<OptionalGroup, OptionalGroup.Builder> {
-        private static readonly OptionalGroup defaultInstance = new Builder().BuildPartial();
+        private static readonly OptionalGroup defaultInstance = new OptionalGroup().MakeReadOnly();
         private static readonly string[] _optionalGroupFieldNames = new string[] { "a" };
         private static readonly uint[] _optionalGroupFieldTags = new uint[] { 136 };
         public static OptionalGroup DefaultInstance {
@@ -1439,7 +1443,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public override OptionalGroup DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override OptionalGroup ThisMessage {
@@ -1525,6 +1529,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static OptionalGroup ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private OptionalGroup MakeReadOnly() {
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -1540,22 +1548,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new OptionalGroup();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(OptionalGroup cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          OptionalGroup result;
+          private bool resultIsReadOnly;
+          private OptionalGroup result;
           
           private OptionalGroup PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               OptionalGroup original = result;
               result = new OptionalGroup();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -1570,13 +1578,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new OptionalGroup();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -1592,11 +1600,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override OptionalGroup BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           public override Builder MergeFrom(pb::IMessage other) {
@@ -1700,7 +1708,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class RepeatedGroup : pb::GeneratedMessage<RepeatedGroup, RepeatedGroup.Builder> {
-        private static readonly RepeatedGroup defaultInstance = new Builder().BuildPartial();
+        private static readonly RepeatedGroup defaultInstance = new RepeatedGroup().MakeReadOnly();
         private static readonly string[] _repeatedGroupFieldNames = new string[] { "a" };
         private static readonly uint[] _repeatedGroupFieldTags = new uint[] { 376 };
         public static RepeatedGroup DefaultInstance {
@@ -1708,7 +1716,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public override RepeatedGroup DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override RepeatedGroup ThisMessage {
@@ -1794,6 +1802,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static RepeatedGroup ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private RepeatedGroup MakeReadOnly() {
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -1809,22 +1821,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new RepeatedGroup();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(RepeatedGroup cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          RepeatedGroup result;
+          private bool resultIsReadOnly;
+          private RepeatedGroup result;
           
           private RepeatedGroup PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               RepeatedGroup original = result;
               result = new RepeatedGroup();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -1839,13 +1851,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new RepeatedGroup();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -1861,11 +1873,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override RepeatedGroup BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           public override Builder MergeFrom(pb::IMessage other) {
@@ -2124,42 +2136,42 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     public const int OptionalGroupFieldNumber = 16;
     private bool hasOptionalGroup;
-    private global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup optionalGroup_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup optionalGroup_;
     public bool HasOptionalGroup {
       get { return hasOptionalGroup; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup OptionalGroup {
-      get { return optionalGroup_; }
+      get { return optionalGroup_ ?? global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup.DefaultInstance; }
     }
     
     public const int OptionalNestedMessageFieldNumber = 18;
     private bool hasOptionalNestedMessage;
-    private global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage optionalNestedMessage_;
     public bool HasOptionalNestedMessage {
       get { return hasOptionalNestedMessage; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage OptionalNestedMessage {
-      get { return optionalNestedMessage_; }
+      get { return optionalNestedMessage_ ?? global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance; }
     }
     
     public const int OptionalForeignMessageFieldNumber = 19;
     private bool hasOptionalForeignMessage;
-    private global::Google.ProtocolBuffers.TestProtos.ForeignMessage optionalForeignMessage_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.ForeignMessage optionalForeignMessage_;
     public bool HasOptionalForeignMessage {
       get { return hasOptionalForeignMessage; }
     }
     public global::Google.ProtocolBuffers.TestProtos.ForeignMessage OptionalForeignMessage {
-      get { return optionalForeignMessage_; }
+      get { return optionalForeignMessage_ ?? global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance; }
     }
     
     public const int OptionalImportMessageFieldNumber = 20;
     private bool hasOptionalImportMessage;
-    private global::Google.ProtocolBuffers.TestProtos.ImportMessage optionalImportMessage_ = global::Google.ProtocolBuffers.TestProtos.ImportMessage.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.ImportMessage optionalImportMessage_;
     public bool HasOptionalImportMessage {
       get { return hasOptionalImportMessage; }
     }
     public global::Google.ProtocolBuffers.TestProtos.ImportMessage OptionalImportMessage {
-      get { return optionalImportMessage_; }
+      get { return optionalImportMessage_ ?? global::Google.ProtocolBuffers.TestProtos.ImportMessage.DefaultInstance; }
     }
     
     public const int OptionalNestedEnumFieldNumber = 21;
@@ -3267,6 +3279,34 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestAllTypes ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestAllTypes MakeReadOnly() {
+      repeatedInt32_.MakeReadOnly();
+      repeatedInt64_.MakeReadOnly();
+      repeatedUint32_.MakeReadOnly();
+      repeatedUint64_.MakeReadOnly();
+      repeatedSint32_.MakeReadOnly();
+      repeatedSint64_.MakeReadOnly();
+      repeatedFixed32_.MakeReadOnly();
+      repeatedFixed64_.MakeReadOnly();
+      repeatedSfixed32_.MakeReadOnly();
+      repeatedSfixed64_.MakeReadOnly();
+      repeatedFloat_.MakeReadOnly();
+      repeatedDouble_.MakeReadOnly();
+      repeatedBool_.MakeReadOnly();
+      repeatedString_.MakeReadOnly();
+      repeatedBytes_.MakeReadOnly();
+      repeatedGroup_.MakeReadOnly();
+      repeatedNestedMessage_.MakeReadOnly();
+      repeatedForeignMessage_.MakeReadOnly();
+      repeatedImportMessage_.MakeReadOnly();
+      repeatedNestedEnum_.MakeReadOnly();
+      repeatedForeignEnum_.MakeReadOnly();
+      repeatedImportEnum_.MakeReadOnly();
+      repeatedStringPiece_.MakeReadOnly();
+      repeatedCord_.MakeReadOnly();
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -3282,22 +3322,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestAllTypes();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestAllTypes cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestAllTypes result;
+      private bool resultIsReadOnly;
+      private TestAllTypes result;
       
       private TestAllTypes PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestAllTypes original = result;
           result = new TestAllTypes();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -3312,13 +3352,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestAllTypes();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -3334,35 +3374,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestAllTypes BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        result.repeatedInt32_.MakeReadOnly();
-        result.repeatedInt64_.MakeReadOnly();
-        result.repeatedUint32_.MakeReadOnly();
-        result.repeatedUint64_.MakeReadOnly();
-        result.repeatedSint32_.MakeReadOnly();
-        result.repeatedSint64_.MakeReadOnly();
-        result.repeatedFixed32_.MakeReadOnly();
-        result.repeatedFixed64_.MakeReadOnly();
-        result.repeatedSfixed32_.MakeReadOnly();
-        result.repeatedSfixed64_.MakeReadOnly();
-        result.repeatedFloat_.MakeReadOnly();
-        result.repeatedDouble_.MakeReadOnly();
-        result.repeatedBool_.MakeReadOnly();
-        result.repeatedString_.MakeReadOnly();
-        result.repeatedBytes_.MakeReadOnly();
-        result.repeatedGroup_.MakeReadOnly();
-        result.repeatedNestedMessage_.MakeReadOnly();
-        result.repeatedForeignMessage_.MakeReadOnly();
-        result.repeatedImportMessage_.MakeReadOnly();
-        result.repeatedNestedEnum_.MakeReadOnly();
-        result.repeatedForeignEnum_.MakeReadOnly();
-        result.repeatedImportEnum_.MakeReadOnly();
-        result.repeatedStringPiece_.MakeReadOnly();
-        result.repeatedCord_.MakeReadOnly();
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -4363,7 +4379,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearOptionalGroup() {
         PrepareBuilder();
         result.hasOptionalGroup = false;
-        result.optionalGroup_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.OptionalGroup.DefaultInstance;
+        result.optionalGroup_ = null;
         return this;
       }
       
@@ -4403,7 +4419,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearOptionalNestedMessage() {
         PrepareBuilder();
         result.hasOptionalNestedMessage = false;
-        result.optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance;
+        result.optionalNestedMessage_ = null;
         return this;
       }
       
@@ -4443,7 +4459,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearOptionalForeignMessage() {
         PrepareBuilder();
         result.hasOptionalForeignMessage = false;
-        result.optionalForeignMessage_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance;
+        result.optionalForeignMessage_ = null;
         return this;
       }
       
@@ -4483,7 +4499,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearOptionalImportMessage() {
         PrepareBuilder();
         result.hasOptionalImportMessage = false;
-        result.optionalImportMessage_ = global::Google.ProtocolBuffers.TestProtos.ImportMessage.DefaultInstance;
+        result.optionalImportMessage_ = null;
         return this;
       }
       
@@ -5814,7 +5830,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestDeprecatedFields : pb::GeneratedMessage<TestDeprecatedFields, TestDeprecatedFields.Builder> {
-    private static readonly TestDeprecatedFields defaultInstance = new Builder().BuildPartial();
+    private static readonly TestDeprecatedFields defaultInstance = new TestDeprecatedFields().MakeReadOnly();
     private static readonly string[] _testDeprecatedFieldsFieldNames = new string[] { "deprecated_int32" };
     private static readonly uint[] _testDeprecatedFieldsFieldTags = new uint[] { 8 };
     public static TestDeprecatedFields DefaultInstance {
@@ -5822,7 +5838,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestDeprecatedFields DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestDeprecatedFields ThisMessage {
@@ -5908,6 +5924,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestDeprecatedFields ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestDeprecatedFields MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -5923,22 +5943,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestDeprecatedFields();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestDeprecatedFields cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestDeprecatedFields result;
+      private bool resultIsReadOnly;
+      private TestDeprecatedFields result;
       
       private TestDeprecatedFields PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestDeprecatedFields original = result;
           result = new TestDeprecatedFields();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -5953,13 +5973,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestDeprecatedFields();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -5975,11 +5995,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestDeprecatedFields BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -6083,7 +6103,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class ForeignMessage : pb::GeneratedMessage<ForeignMessage, ForeignMessage.Builder> {
-    private static readonly ForeignMessage defaultInstance = new Builder().BuildPartial();
+    private static readonly ForeignMessage defaultInstance = new ForeignMessage().MakeReadOnly();
     private static readonly string[] _foreignMessageFieldNames = new string[] { "c" };
     private static readonly uint[] _foreignMessageFieldTags = new uint[] { 8 };
     public static ForeignMessage DefaultInstance {
@@ -6091,7 +6111,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override ForeignMessage DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override ForeignMessage ThisMessage {
@@ -6177,6 +6197,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static ForeignMessage ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private ForeignMessage MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -6192,22 +6216,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new ForeignMessage();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(ForeignMessage cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      ForeignMessage result;
+      private bool resultIsReadOnly;
+      private ForeignMessage result;
       
       private ForeignMessage PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           ForeignMessage original = result;
           result = new ForeignMessage();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -6222,13 +6246,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new ForeignMessage();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -6244,11 +6268,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override ForeignMessage BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -6352,7 +6376,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestAllExtensions : pb::ExtendableMessage<TestAllExtensions, TestAllExtensions.Builder> {
-    private static readonly TestAllExtensions defaultInstance = new Builder().BuildPartial();
+    private static readonly TestAllExtensions defaultInstance = new TestAllExtensions().MakeReadOnly();
     private static readonly string[] _testAllExtensionsFieldNames = new string[] {  };
     private static readonly uint[] _testAllExtensionsFieldTags = new uint[] {  };
     public static TestAllExtensions DefaultInstance {
@@ -6360,7 +6384,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestAllExtensions DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestAllExtensions ThisMessage {
@@ -6434,6 +6458,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestAllExtensions ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestAllExtensions MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -6449,22 +6477,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestAllExtensions();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestAllExtensions cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestAllExtensions result;
+      private bool resultIsReadOnly;
+      private TestAllExtensions result;
       
       private TestAllExtensions PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestAllExtensions original = result;
           result = new TestAllExtensions();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -6479,13 +6507,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestAllExtensions();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -6501,11 +6529,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestAllExtensions BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -6583,7 +6611,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class OptionalGroup_extension : pb::GeneratedMessage<OptionalGroup_extension, OptionalGroup_extension.Builder> {
-    private static readonly OptionalGroup_extension defaultInstance = new Builder().BuildPartial();
+    private static readonly OptionalGroup_extension defaultInstance = new OptionalGroup_extension().MakeReadOnly();
     private static readonly string[] _optionalGroupExtensionFieldNames = new string[] { "a" };
     private static readonly uint[] _optionalGroupExtensionFieldTags = new uint[] { 136 };
     public static OptionalGroup_extension DefaultInstance {
@@ -6591,7 +6619,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override OptionalGroup_extension DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override OptionalGroup_extension ThisMessage {
@@ -6677,6 +6705,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static OptionalGroup_extension ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private OptionalGroup_extension MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -6692,22 +6724,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new OptionalGroup_extension();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(OptionalGroup_extension cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      OptionalGroup_extension result;
+      private bool resultIsReadOnly;
+      private OptionalGroup_extension result;
       
       private OptionalGroup_extension PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           OptionalGroup_extension original = result;
           result = new OptionalGroup_extension();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -6722,13 +6754,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new OptionalGroup_extension();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -6744,11 +6776,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override OptionalGroup_extension BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -6852,7 +6884,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class RepeatedGroup_extension : pb::GeneratedMessage<RepeatedGroup_extension, RepeatedGroup_extension.Builder> {
-    private static readonly RepeatedGroup_extension defaultInstance = new Builder().BuildPartial();
+    private static readonly RepeatedGroup_extension defaultInstance = new RepeatedGroup_extension().MakeReadOnly();
     private static readonly string[] _repeatedGroupExtensionFieldNames = new string[] { "a" };
     private static readonly uint[] _repeatedGroupExtensionFieldTags = new uint[] { 376 };
     public static RepeatedGroup_extension DefaultInstance {
@@ -6860,7 +6892,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override RepeatedGroup_extension DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override RepeatedGroup_extension ThisMessage {
@@ -6946,6 +6978,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static RepeatedGroup_extension ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private RepeatedGroup_extension MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -6961,22 +6997,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new RepeatedGroup_extension();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(RepeatedGroup_extension cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      RepeatedGroup_extension result;
+      private bool resultIsReadOnly;
+      private RepeatedGroup_extension result;
       
       private RepeatedGroup_extension PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           RepeatedGroup_extension original = result;
           result = new RepeatedGroup_extension();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -6991,13 +7027,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new RepeatedGroup_extension();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -7013,11 +7049,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override RepeatedGroup_extension BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -7121,7 +7157,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestNestedExtension : pb::GeneratedMessage<TestNestedExtension, TestNestedExtension.Builder> {
-    private static readonly TestNestedExtension defaultInstance = new Builder().BuildPartial();
+    private static readonly TestNestedExtension defaultInstance = new TestNestedExtension().MakeReadOnly();
     private static readonly string[] _testNestedExtensionFieldNames = new string[] {  };
     private static readonly uint[] _testNestedExtensionFieldTags = new uint[] {  };
     public static TestNestedExtension DefaultInstance {
@@ -7129,7 +7165,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestNestedExtension DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestNestedExtension ThisMessage {
@@ -7201,6 +7237,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestNestedExtension ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestNestedExtension MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -7216,22 +7256,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestNestedExtension();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestNestedExtension cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestNestedExtension result;
+      private bool resultIsReadOnly;
+      private TestNestedExtension result;
       
       private TestNestedExtension PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestNestedExtension original = result;
           result = new TestNestedExtension();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -7246,13 +7286,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestNestedExtension();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -7268,11 +7308,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestNestedExtension BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -7349,7 +7389,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestRequired : pb::GeneratedMessage<TestRequired, TestRequired.Builder> {
-    private static readonly TestRequired defaultInstance = new Builder().BuildPartial();
+    private static readonly TestRequired defaultInstance = new TestRequired().MakeReadOnly();
     private static readonly string[] _testRequiredFieldNames = new string[] { "a", "b", "c", "dummy10", "dummy11", "dummy12", "dummy13", "dummy14", "dummy15", "dummy16", "dummy17", "dummy18", "dummy19", "dummy2", "dummy20", "dummy21", "dummy22", "dummy23", "dummy24", "dummy25", "dummy26", "dummy27", "dummy28", "dummy29", "dummy30", "dummy31", "dummy32", "dummy4", "dummy5", "dummy6", "dummy7", "dummy8", "dummy9" };
     private static readonly uint[] _testRequiredFieldTags = new uint[] { 8, 24, 264, 80, 88, 96, 104, 112, 120, 128, 136, 144, 152, 16, 160, 168, 176, 184, 192, 200, 208, 216, 224, 232, 240, 248, 256, 32, 40, 48, 56, 64, 72 };
     public static TestRequired DefaultInstance {
@@ -7357,7 +7397,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestRequired DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestRequired ThisMessage {
@@ -7962,6 +8002,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestRequired ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestRequired MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -7977,22 +8021,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestRequired();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestRequired cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestRequired result;
+      private bool resultIsReadOnly;
+      private TestRequired result;
       
       private TestRequired PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestRequired original = result;
           result = new TestRequired();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -8007,13 +8051,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestRequired();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -8029,11 +8073,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestRequired BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -9001,7 +9045,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestRequiredForeign : pb::GeneratedMessage<TestRequiredForeign, TestRequiredForeign.Builder> {
-    private static readonly TestRequiredForeign defaultInstance = new Builder().BuildPartial();
+    private static readonly TestRequiredForeign defaultInstance = new TestRequiredForeign().MakeReadOnly();
     private static readonly string[] _testRequiredForeignFieldNames = new string[] { "dummy", "optional_message", "repeated_message" };
     private static readonly uint[] _testRequiredForeignFieldTags = new uint[] { 24, 10, 18 };
     public static TestRequiredForeign DefaultInstance {
@@ -9009,7 +9053,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestRequiredForeign DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestRequiredForeign ThisMessage {
@@ -9026,12 +9070,12 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     public const int OptionalMessageFieldNumber = 1;
     private bool hasOptionalMessage;
-    private global::Google.ProtocolBuffers.TestProtos.TestRequired optionalMessage_ = global::Google.ProtocolBuffers.TestProtos.TestRequired.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestRequired optionalMessage_;
     public bool HasOptionalMessage {
       get { return hasOptionalMessage; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestRequired OptionalMessage {
-      get { return optionalMessage_; }
+      get { return optionalMessage_ ?? global::Google.ProtocolBuffers.TestProtos.TestRequired.DefaultInstance; }
     }
     
     public const int RepeatedMessageFieldNumber = 2;
@@ -9135,6 +9179,11 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestRequiredForeign ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestRequiredForeign MakeReadOnly() {
+      repeatedMessage_.MakeReadOnly();
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -9150,22 +9199,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestRequiredForeign();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestRequiredForeign cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestRequiredForeign result;
+      private bool resultIsReadOnly;
+      private TestRequiredForeign result;
       
       private TestRequiredForeign PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestRequiredForeign original = result;
           result = new TestRequiredForeign();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -9180,13 +9229,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestRequiredForeign();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -9202,12 +9251,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestRequiredForeign BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        result.repeatedMessage_.MakeReadOnly();
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -9337,7 +9385,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearOptionalMessage() {
         PrepareBuilder();
         result.hasOptionalMessage = false;
-        result.optionalMessage_ = global::Google.ProtocolBuffers.TestProtos.TestRequired.DefaultInstance;
+        result.optionalMessage_ = null;
         return this;
       }
       
@@ -9414,7 +9462,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestForeignNested : pb::GeneratedMessage<TestForeignNested, TestForeignNested.Builder> {
-    private static readonly TestForeignNested defaultInstance = new Builder().BuildPartial();
+    private static readonly TestForeignNested defaultInstance = new TestForeignNested().MakeReadOnly();
     private static readonly string[] _testForeignNestedFieldNames = new string[] { "foreign_nested" };
     private static readonly uint[] _testForeignNestedFieldTags = new uint[] { 10 };
     public static TestForeignNested DefaultInstance {
@@ -9422,7 +9470,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestForeignNested DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestForeignNested ThisMessage {
@@ -9439,12 +9487,12 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     public const int ForeignNestedFieldNumber = 1;
     private bool hasForeignNested;
-    private global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage foreignNested_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage foreignNested_;
     public bool HasForeignNested {
       get { return hasForeignNested; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage ForeignNested {
-      get { return foreignNested_; }
+      get { return foreignNested_ ?? global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance; }
     }
     
     public override bool IsInitialized {
@@ -9508,6 +9556,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestForeignNested ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestForeignNested MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -9523,22 +9575,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestForeignNested();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestForeignNested cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestForeignNested result;
+      private bool resultIsReadOnly;
+      private TestForeignNested result;
       
       private TestForeignNested PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestForeignNested original = result;
           result = new TestForeignNested();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -9553,13 +9605,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestForeignNested();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -9575,11 +9627,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestForeignNested BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -9695,7 +9747,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearForeignNested() {
         PrepareBuilder();
         result.hasForeignNested = false;
-        result.foreignNested_ = global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.DefaultInstance;
+        result.foreignNested_ = null;
         return this;
       }
     }
@@ -9708,7 +9760,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestEmptyMessage : pb::GeneratedMessage<TestEmptyMessage, TestEmptyMessage.Builder> {
-    private static readonly TestEmptyMessage defaultInstance = new Builder().BuildPartial();
+    private static readonly TestEmptyMessage defaultInstance = new TestEmptyMessage().MakeReadOnly();
     private static readonly string[] _testEmptyMessageFieldNames = new string[] {  };
     private static readonly uint[] _testEmptyMessageFieldTags = new uint[] {  };
     public static TestEmptyMessage DefaultInstance {
@@ -9716,7 +9768,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestEmptyMessage DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestEmptyMessage ThisMessage {
@@ -9786,6 +9838,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestEmptyMessage ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestEmptyMessage MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -9801,22 +9857,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestEmptyMessage();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestEmptyMessage cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestEmptyMessage result;
+      private bool resultIsReadOnly;
+      private TestEmptyMessage result;
       
       private TestEmptyMessage PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestEmptyMessage original = result;
           result = new TestEmptyMessage();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -9831,13 +9887,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestEmptyMessage();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -9853,11 +9909,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestEmptyMessage BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -9934,7 +9990,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestEmptyMessageWithExtensions : pb::ExtendableMessage<TestEmptyMessageWithExtensions, TestEmptyMessageWithExtensions.Builder> {
-    private static readonly TestEmptyMessageWithExtensions defaultInstance = new Builder().BuildPartial();
+    private static readonly TestEmptyMessageWithExtensions defaultInstance = new TestEmptyMessageWithExtensions().MakeReadOnly();
     private static readonly string[] _testEmptyMessageWithExtensionsFieldNames = new string[] {  };
     private static readonly uint[] _testEmptyMessageWithExtensionsFieldTags = new uint[] {  };
     public static TestEmptyMessageWithExtensions DefaultInstance {
@@ -9942,7 +9998,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestEmptyMessageWithExtensions DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestEmptyMessageWithExtensions ThisMessage {
@@ -10016,6 +10072,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestEmptyMessageWithExtensions ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestEmptyMessageWithExtensions MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -10031,22 +10091,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestEmptyMessageWithExtensions();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestEmptyMessageWithExtensions cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestEmptyMessageWithExtensions result;
+      private bool resultIsReadOnly;
+      private TestEmptyMessageWithExtensions result;
       
       private TestEmptyMessageWithExtensions PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestEmptyMessageWithExtensions original = result;
           result = new TestEmptyMessageWithExtensions();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -10061,13 +10121,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestEmptyMessageWithExtensions();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -10083,11 +10143,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestEmptyMessageWithExtensions BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -10165,7 +10225,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestMultipleExtensionRanges : pb::ExtendableMessage<TestMultipleExtensionRanges, TestMultipleExtensionRanges.Builder> {
-    private static readonly TestMultipleExtensionRanges defaultInstance = new Builder().BuildPartial();
+    private static readonly TestMultipleExtensionRanges defaultInstance = new TestMultipleExtensionRanges().MakeReadOnly();
     private static readonly string[] _testMultipleExtensionRangesFieldNames = new string[] {  };
     private static readonly uint[] _testMultipleExtensionRangesFieldTags = new uint[] {  };
     public static TestMultipleExtensionRanges DefaultInstance {
@@ -10173,7 +10233,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestMultipleExtensionRanges DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestMultipleExtensionRanges ThisMessage {
@@ -10249,6 +10309,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestMultipleExtensionRanges ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestMultipleExtensionRanges MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -10264,22 +10328,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestMultipleExtensionRanges();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestMultipleExtensionRanges cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestMultipleExtensionRanges result;
+      private bool resultIsReadOnly;
+      private TestMultipleExtensionRanges result;
       
       private TestMultipleExtensionRanges PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestMultipleExtensionRanges original = result;
           result = new TestMultipleExtensionRanges();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -10294,13 +10358,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestMultipleExtensionRanges();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -10316,11 +10380,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestMultipleExtensionRanges BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -10398,7 +10462,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestReallyLargeTagNumber : pb::GeneratedMessage<TestReallyLargeTagNumber, TestReallyLargeTagNumber.Builder> {
-    private static readonly TestReallyLargeTagNumber defaultInstance = new Builder().BuildPartial();
+    private static readonly TestReallyLargeTagNumber defaultInstance = new TestReallyLargeTagNumber().MakeReadOnly();
     private static readonly string[] _testReallyLargeTagNumberFieldNames = new string[] { "a", "bb" };
     private static readonly uint[] _testReallyLargeTagNumberFieldTags = new uint[] { 8, 2147483640 };
     public static TestReallyLargeTagNumber DefaultInstance {
@@ -10406,7 +10470,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestReallyLargeTagNumber DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestReallyLargeTagNumber ThisMessage {
@@ -10508,6 +10572,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestReallyLargeTagNumber ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestReallyLargeTagNumber MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -10523,22 +10591,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestReallyLargeTagNumber();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestReallyLargeTagNumber cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestReallyLargeTagNumber result;
+      private bool resultIsReadOnly;
+      private TestReallyLargeTagNumber result;
       
       private TestReallyLargeTagNumber PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestReallyLargeTagNumber original = result;
           result = new TestReallyLargeTagNumber();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -10553,13 +10621,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestReallyLargeTagNumber();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -10575,11 +10643,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestReallyLargeTagNumber BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -10710,7 +10778,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestRecursiveMessage : pb::GeneratedMessage<TestRecursiveMessage, TestRecursiveMessage.Builder> {
-    private static readonly TestRecursiveMessage defaultInstance = new Builder().BuildPartial();
+    private static readonly TestRecursiveMessage defaultInstance = new TestRecursiveMessage().MakeReadOnly();
     private static readonly string[] _testRecursiveMessageFieldNames = new string[] { "a", "i" };
     private static readonly uint[] _testRecursiveMessageFieldTags = new uint[] { 10, 16 };
     public static TestRecursiveMessage DefaultInstance {
@@ -10718,7 +10786,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestRecursiveMessage DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestRecursiveMessage ThisMessage {
@@ -10735,12 +10803,12 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     public const int AFieldNumber = 1;
     private bool hasA;
-    private global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage a_ = global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage a_;
     public bool HasA {
       get { return hasA; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage A {
-      get { return a_; }
+      get { return a_ ?? global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage.DefaultInstance; }
     }
     
     public const int IFieldNumber = 2;
@@ -10820,6 +10888,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestRecursiveMessage ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestRecursiveMessage MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -10835,22 +10907,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestRecursiveMessage();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestRecursiveMessage cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestRecursiveMessage result;
+      private bool resultIsReadOnly;
+      private TestRecursiveMessage result;
       
       private TestRecursiveMessage PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestRecursiveMessage original = result;
           result = new TestRecursiveMessage();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -10865,13 +10937,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestRecursiveMessage();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -10887,11 +10959,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestRecursiveMessage BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -11014,7 +11086,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearA() {
         PrepareBuilder();
         result.hasA = false;
-        result.a_ = global::Google.ProtocolBuffers.TestProtos.TestRecursiveMessage.DefaultInstance;
+        result.a_ = null;
         return this;
       }
       
@@ -11047,7 +11119,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestMutualRecursionA : pb::GeneratedMessage<TestMutualRecursionA, TestMutualRecursionA.Builder> {
-    private static readonly TestMutualRecursionA defaultInstance = new Builder().BuildPartial();
+    private static readonly TestMutualRecursionA defaultInstance = new TestMutualRecursionA().MakeReadOnly();
     private static readonly string[] _testMutualRecursionAFieldNames = new string[] { "bb" };
     private static readonly uint[] _testMutualRecursionAFieldTags = new uint[] { 10 };
     public static TestMutualRecursionA DefaultInstance {
@@ -11055,7 +11127,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestMutualRecursionA DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestMutualRecursionA ThisMessage {
@@ -11072,12 +11144,12 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     public const int BbFieldNumber = 1;
     private bool hasBb;
-    private global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB bb_ = global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB bb_;
     public bool HasBb {
       get { return hasBb; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB Bb {
-      get { return bb_; }
+      get { return bb_ ?? global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB.DefaultInstance; }
     }
     
     public override bool IsInitialized {
@@ -11141,6 +11213,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestMutualRecursionA ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestMutualRecursionA MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -11156,22 +11232,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestMutualRecursionA();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestMutualRecursionA cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestMutualRecursionA result;
+      private bool resultIsReadOnly;
+      private TestMutualRecursionA result;
       
       private TestMutualRecursionA PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestMutualRecursionA original = result;
           result = new TestMutualRecursionA();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -11186,13 +11262,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestMutualRecursionA();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -11208,11 +11284,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestMutualRecursionA BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -11328,7 +11404,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearBb() {
         PrepareBuilder();
         result.hasBb = false;
-        result.bb_ = global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionB.DefaultInstance;
+        result.bb_ = null;
         return this;
       }
     }
@@ -11341,7 +11417,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestMutualRecursionB : pb::GeneratedMessage<TestMutualRecursionB, TestMutualRecursionB.Builder> {
-    private static readonly TestMutualRecursionB defaultInstance = new Builder().BuildPartial();
+    private static readonly TestMutualRecursionB defaultInstance = new TestMutualRecursionB().MakeReadOnly();
     private static readonly string[] _testMutualRecursionBFieldNames = new string[] { "a", "optional_int32" };
     private static readonly uint[] _testMutualRecursionBFieldTags = new uint[] { 10, 16 };
     public static TestMutualRecursionB DefaultInstance {
@@ -11349,7 +11425,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestMutualRecursionB DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestMutualRecursionB ThisMessage {
@@ -11366,12 +11442,12 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     public const int AFieldNumber = 1;
     private bool hasA;
-    private global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA a_ = global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA a_;
     public bool HasA {
       get { return hasA; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA A {
-      get { return a_; }
+      get { return a_ ?? global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA.DefaultInstance; }
     }
     
     public const int OptionalInt32FieldNumber = 2;
@@ -11451,6 +11527,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestMutualRecursionB ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestMutualRecursionB MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -11466,22 +11546,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestMutualRecursionB();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestMutualRecursionB cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestMutualRecursionB result;
+      private bool resultIsReadOnly;
+      private TestMutualRecursionB result;
       
       private TestMutualRecursionB PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestMutualRecursionB original = result;
           result = new TestMutualRecursionB();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -11496,13 +11576,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestMutualRecursionB();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -11518,11 +11598,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestMutualRecursionB BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -11645,7 +11725,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearA() {
         PrepareBuilder();
         result.hasA = false;
-        result.a_ = global::Google.ProtocolBuffers.TestProtos.TestMutualRecursionA.DefaultInstance;
+        result.a_ = null;
         return this;
       }
       
@@ -11678,7 +11758,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestDupFieldNumber : pb::GeneratedMessage<TestDupFieldNumber, TestDupFieldNumber.Builder> {
-    private static readonly TestDupFieldNumber defaultInstance = new Builder().BuildPartial();
+    private static readonly TestDupFieldNumber defaultInstance = new TestDupFieldNumber().MakeReadOnly();
     private static readonly string[] _testDupFieldNumberFieldNames = new string[] { "a", "bar", "foo" };
     private static readonly uint[] _testDupFieldNumberFieldTags = new uint[] { 8, 27, 19 };
     public static TestDupFieldNumber DefaultInstance {
@@ -11686,7 +11766,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestDupFieldNumber DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestDupFieldNumber ThisMessage {
@@ -11710,7 +11790,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class Foo : pb::GeneratedMessage<Foo, Foo.Builder> {
-        private static readonly Foo defaultInstance = new Builder().BuildPartial();
+        private static readonly Foo defaultInstance = new Foo().MakeReadOnly();
         private static readonly string[] _fooFieldNames = new string[] { "a" };
         private static readonly uint[] _fooFieldTags = new uint[] { 8 };
         public static Foo DefaultInstance {
@@ -11718,7 +11798,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public override Foo DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override Foo ThisMessage {
@@ -11804,6 +11884,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static Foo ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private Foo MakeReadOnly() {
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -11819,22 +11903,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new Foo();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(Foo cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          Foo result;
+          private bool resultIsReadOnly;
+          private Foo result;
           
           private Foo PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               Foo original = result;
               result = new Foo();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -11849,13 +11933,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new Foo();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -11871,11 +11955,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Foo BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           public override Builder MergeFrom(pb::IMessage other) {
@@ -11979,7 +12063,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class Bar : pb::GeneratedMessage<Bar, Bar.Builder> {
-        private static readonly Bar defaultInstance = new Builder().BuildPartial();
+        private static readonly Bar defaultInstance = new Bar().MakeReadOnly();
         private static readonly string[] _barFieldNames = new string[] { "a" };
         private static readonly uint[] _barFieldTags = new uint[] { 8 };
         public static Bar DefaultInstance {
@@ -11987,7 +12071,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public override Bar DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override Bar ThisMessage {
@@ -12073,6 +12157,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static Bar ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private Bar MakeReadOnly() {
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -12088,22 +12176,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new Bar();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(Bar cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          Bar result;
+          private bool resultIsReadOnly;
+          private Bar result;
           
           private Bar PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               Bar original = result;
               result = new Bar();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -12118,13 +12206,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new Bar();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -12140,11 +12228,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Bar BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           public override Builder MergeFrom(pb::IMessage other) {
@@ -12259,22 +12347,22 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     public const int FooFieldNumber = 2;
     private bool hasFoo;
-    private global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo foo_ = global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo foo_;
     public bool HasFoo {
       get { return hasFoo; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo Foo {
-      get { return foo_; }
+      get { return foo_ ?? global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo.DefaultInstance; }
     }
     
     public const int BarFieldNumber = 3;
     private bool hasBar;
-    private global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar bar_ = global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar bar_;
     public bool HasBar {
       get { return hasBar; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar Bar {
-      get { return bar_; }
+      get { return bar_ ?? global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar.DefaultInstance; }
     }
     
     public override bool IsInitialized {
@@ -12350,6 +12438,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestDupFieldNumber ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestDupFieldNumber MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -12365,22 +12457,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestDupFieldNumber();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestDupFieldNumber cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestDupFieldNumber result;
+      private bool resultIsReadOnly;
+      private TestDupFieldNumber result;
       
       private TestDupFieldNumber PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestDupFieldNumber original = result;
           result = new TestDupFieldNumber();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -12395,13 +12487,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestDupFieldNumber();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -12417,11 +12509,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestDupFieldNumber BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -12576,7 +12668,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearFoo() {
         PrepareBuilder();
         result.hasFoo = false;
-        result.foo_ = global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Foo.DefaultInstance;
+        result.foo_ = null;
         return this;
       }
       
@@ -12616,7 +12708,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearBar() {
         PrepareBuilder();
         result.hasBar = false;
-        result.bar_ = global::Google.ProtocolBuffers.TestProtos.TestDupFieldNumber.Types.Bar.DefaultInstance;
+        result.bar_ = null;
         return this;
       }
     }
@@ -12629,7 +12721,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestNestedMessageHasBits : pb::GeneratedMessage<TestNestedMessageHasBits, TestNestedMessageHasBits.Builder> {
-    private static readonly TestNestedMessageHasBits defaultInstance = new Builder().BuildPartial();
+    private static readonly TestNestedMessageHasBits defaultInstance = new TestNestedMessageHasBits().MakeReadOnly();
     private static readonly string[] _testNestedMessageHasBitsFieldNames = new string[] { "optional_nested_message" };
     private static readonly uint[] _testNestedMessageHasBitsFieldTags = new uint[] { 10 };
     public static TestNestedMessageHasBits DefaultInstance {
@@ -12637,7 +12729,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestNestedMessageHasBits DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestNestedMessageHasBits ThisMessage {
@@ -12661,7 +12753,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class NestedMessage : pb::GeneratedMessage<NestedMessage, NestedMessage.Builder> {
-        private static readonly NestedMessage defaultInstance = new Builder().BuildPartial();
+        private static readonly NestedMessage defaultInstance = new NestedMessage().MakeReadOnly();
         private static readonly string[] _nestedMessageFieldNames = new string[] { "nestedmessage_repeated_foreignmessage", "nestedmessage_repeated_int32" };
         private static readonly uint[] _nestedMessageFieldTags = new uint[] { 18, 8 };
         public static NestedMessage DefaultInstance {
@@ -12669,7 +12761,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public override NestedMessage DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override NestedMessage ThisMessage {
@@ -12780,6 +12872,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static NestedMessage ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private NestedMessage MakeReadOnly() {
+          nestedmessageRepeatedInt32_.MakeReadOnly();
+          nestedmessageRepeatedForeignmessage_.MakeReadOnly();
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -12795,22 +12893,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new NestedMessage();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(NestedMessage cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          NestedMessage result;
+          private bool resultIsReadOnly;
+          private NestedMessage result;
           
           private NestedMessage PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               NestedMessage original = result;
               result = new NestedMessage();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -12825,13 +12923,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new NestedMessage();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -12847,13 +12945,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override NestedMessage BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            result.nestedmessageRepeatedInt32_.MakeReadOnly();
-            result.nestedmessageRepeatedForeignmessage_.MakeReadOnly();
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           public override Builder MergeFrom(pb::IMessage other) {
@@ -13020,12 +13116,12 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     public const int OptionalNestedMessageFieldNumber = 1;
     private bool hasOptionalNestedMessage;
-    private global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage optionalNestedMessage_;
     public bool HasOptionalNestedMessage {
       get { return hasOptionalNestedMessage; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage OptionalNestedMessage {
-      get { return optionalNestedMessage_; }
+      get { return optionalNestedMessage_ ?? global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage.DefaultInstance; }
     }
     
     public override bool IsInitialized {
@@ -13089,6 +13185,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestNestedMessageHasBits ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestNestedMessageHasBits MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -13104,22 +13204,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestNestedMessageHasBits();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestNestedMessageHasBits cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestNestedMessageHasBits result;
+      private bool resultIsReadOnly;
+      private TestNestedMessageHasBits result;
       
       private TestNestedMessageHasBits PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestNestedMessageHasBits original = result;
           result = new TestNestedMessageHasBits();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -13134,13 +13234,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestNestedMessageHasBits();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -13156,11 +13256,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestNestedMessageHasBits BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -13276,7 +13376,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearOptionalNestedMessage() {
         PrepareBuilder();
         result.hasOptionalNestedMessage = false;
-        result.optionalNestedMessage_ = global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage.DefaultInstance;
+        result.optionalNestedMessage_ = null;
         return this;
       }
     }
@@ -13289,7 +13389,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestCamelCaseFieldNames : pb::GeneratedMessage<TestCamelCaseFieldNames, TestCamelCaseFieldNames.Builder> {
-    private static readonly TestCamelCaseFieldNames defaultInstance = new Builder().BuildPartial();
+    private static readonly TestCamelCaseFieldNames defaultInstance = new TestCamelCaseFieldNames().MakeReadOnly();
     private static readonly string[] _testCamelCaseFieldNamesFieldNames = new string[] { "CordField", "EnumField", "MessageField", "PrimitiveField", "RepeatedCordField", "RepeatedEnumField", "RepeatedMessageField", "RepeatedPrimitiveField", "RepeatedStringField", "RepeatedStringPieceField", "StringField", "StringPieceField" };
     private static readonly uint[] _testCamelCaseFieldNamesFieldTags = new uint[] { 50, 24, 34, 8, 98, 72, 82, 56, 66, 90, 18, 42 };
     public static TestCamelCaseFieldNames DefaultInstance {
@@ -13297,7 +13397,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestCamelCaseFieldNames DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestCamelCaseFieldNames ThisMessage {
@@ -13344,12 +13444,12 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     public const int MessageFieldFieldNumber = 4;
     private bool hasMessageField;
-    private global::Google.ProtocolBuffers.TestProtos.ForeignMessage messageField_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.ForeignMessage messageField_;
     public bool HasMessageField {
       get { return hasMessageField; }
     }
     public global::Google.ProtocolBuffers.TestProtos.ForeignMessage MessageField {
-      get { return messageField_; }
+      get { return messageField_ ?? global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance; }
     }
     
     public const int StringPieceFieldFieldNumber = 5;
@@ -13598,6 +13698,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestCamelCaseFieldNames ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestCamelCaseFieldNames MakeReadOnly() {
+      repeatedPrimitiveField_.MakeReadOnly();
+      repeatedStringField_.MakeReadOnly();
+      repeatedEnumField_.MakeReadOnly();
+      repeatedMessageField_.MakeReadOnly();
+      repeatedStringPieceField_.MakeReadOnly();
+      repeatedCordField_.MakeReadOnly();
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -13613,22 +13723,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestCamelCaseFieldNames();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestCamelCaseFieldNames cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestCamelCaseFieldNames result;
+      private bool resultIsReadOnly;
+      private TestCamelCaseFieldNames result;
       
       private TestCamelCaseFieldNames PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestCamelCaseFieldNames original = result;
           result = new TestCamelCaseFieldNames();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -13643,13 +13753,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestCamelCaseFieldNames();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -13665,17 +13775,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestCamelCaseFieldNames BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        result.repeatedPrimitiveField_.MakeReadOnly();
-        result.repeatedStringField_.MakeReadOnly();
-        result.repeatedEnumField_.MakeReadOnly();
-        result.repeatedMessageField_.MakeReadOnly();
-        result.repeatedStringPieceField_.MakeReadOnly();
-        result.repeatedCordField_.MakeReadOnly();
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -13948,7 +14052,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearMessageField() {
         PrepareBuilder();
         result.hasMessageField = false;
-        result.messageField_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance;
+        result.messageField_ = null;
         return this;
       }
       
@@ -14203,7 +14307,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestFieldOrderings : pb::ExtendableMessage<TestFieldOrderings, TestFieldOrderings.Builder> {
-    private static readonly TestFieldOrderings defaultInstance = new Builder().BuildPartial();
+    private static readonly TestFieldOrderings defaultInstance = new TestFieldOrderings().MakeReadOnly();
     private static readonly string[] _testFieldOrderingsFieldNames = new string[] { "my_float", "my_int", "my_string" };
     private static readonly uint[] _testFieldOrderingsFieldTags = new uint[] { 813, 8, 90 };
     public static TestFieldOrderings DefaultInstance {
@@ -14211,7 +14315,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestFieldOrderings DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestFieldOrderings ThisMessage {
@@ -14334,6 +14438,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestFieldOrderings ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestFieldOrderings MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -14349,22 +14457,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestFieldOrderings();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestFieldOrderings cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestFieldOrderings result;
+      private bool resultIsReadOnly;
+      private TestFieldOrderings result;
       
       private TestFieldOrderings PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestFieldOrderings original = result;
           result = new TestFieldOrderings();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -14379,13 +14487,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestFieldOrderings();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -14401,11 +14509,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestFieldOrderings BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -14565,7 +14673,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestExtremeDefaultValues : pb::GeneratedMessage<TestExtremeDefaultValues, TestExtremeDefaultValues.Builder> {
-    private static readonly TestExtremeDefaultValues defaultInstance = new Builder().BuildPartial();
+    private static readonly TestExtremeDefaultValues defaultInstance = new TestExtremeDefaultValues().MakeReadOnly();
     private static readonly string[] _testExtremeDefaultValuesFieldNames = new string[] { "escaped_bytes", "inf_double", "inf_float", "large_float", "large_uint32", "large_uint64", "nan_double", "nan_float", "neg_inf_double", "neg_inf_float", "negative_float", "negative_one_float", "one_float", "small_float", "small_int32", "small_int64", "small_negative_float", "utf8_string", "zero_float" };
     private static readonly uint[] _testExtremeDefaultValuesFieldTags = new uint[] { 10, 113, 141, 101, 16, 24, 129, 157, 121, 149, 93, 85, 69, 77, 32, 40, 109, 50, 61 };
     public static TestExtremeDefaultValues DefaultInstance {
@@ -14573,7 +14681,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestExtremeDefaultValues DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestExtremeDefaultValues ThisMessage {
@@ -14949,6 +15057,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestExtremeDefaultValues ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestExtremeDefaultValues MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -14964,22 +15076,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestExtremeDefaultValues();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestExtremeDefaultValues cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestExtremeDefaultValues result;
+      private bool resultIsReadOnly;
+      private TestExtremeDefaultValues result;
       
       private TestExtremeDefaultValues PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestExtremeDefaultValues original = result;
           result = new TestExtremeDefaultValues();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -14994,13 +15106,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestExtremeDefaultValues();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -15016,11 +15128,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestExtremeDefaultValues BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -15616,7 +15728,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class OneString : pb::GeneratedMessage<OneString, OneString.Builder> {
-    private static readonly OneString defaultInstance = new Builder().BuildPartial();
+    private static readonly OneString defaultInstance = new OneString().MakeReadOnly();
     private static readonly string[] _oneStringFieldNames = new string[] { "data" };
     private static readonly uint[] _oneStringFieldTags = new uint[] { 10 };
     public static OneString DefaultInstance {
@@ -15624,7 +15736,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override OneString DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override OneString ThisMessage {
@@ -15710,6 +15822,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static OneString ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private OneString MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -15725,22 +15841,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new OneString();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(OneString cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      OneString result;
+      private bool resultIsReadOnly;
+      private OneString result;
       
       private OneString PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           OneString original = result;
           result = new OneString();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -15755,13 +15871,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new OneString();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -15777,11 +15893,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override OneString BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -15886,7 +16002,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class OneBytes : pb::GeneratedMessage<OneBytes, OneBytes.Builder> {
-    private static readonly OneBytes defaultInstance = new Builder().BuildPartial();
+    private static readonly OneBytes defaultInstance = new OneBytes().MakeReadOnly();
     private static readonly string[] _oneBytesFieldNames = new string[] { "data" };
     private static readonly uint[] _oneBytesFieldTags = new uint[] { 10 };
     public static OneBytes DefaultInstance {
@@ -15894,7 +16010,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override OneBytes DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override OneBytes ThisMessage {
@@ -15980,6 +16096,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static OneBytes ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private OneBytes MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -15995,22 +16115,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new OneBytes();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(OneBytes cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      OneBytes result;
+      private bool resultIsReadOnly;
+      private OneBytes result;
       
       private OneBytes PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           OneBytes original = result;
           result = new OneBytes();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -16025,13 +16145,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new OneBytes();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -16047,11 +16167,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override OneBytes BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -16156,7 +16276,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestPackedTypes : pb::GeneratedMessage<TestPackedTypes, TestPackedTypes.Builder> {
-    private static readonly TestPackedTypes defaultInstance = new Builder().BuildPartial();
+    private static readonly TestPackedTypes defaultInstance = new TestPackedTypes().MakeReadOnly();
     private static readonly string[] _testPackedTypesFieldNames = new string[] { "packed_bool", "packed_double", "packed_enum", "packed_fixed32", "packed_fixed64", "packed_float", "packed_int32", "packed_int64", "packed_sfixed32", "packed_sfixed64", "packed_sint32", "packed_sint64", "packed_uint32", "packed_uint64" };
     private static readonly uint[] _testPackedTypesFieldTags = new uint[] { 818, 810, 826, 770, 778, 802, 722, 730, 786, 794, 754, 762, 738, 746 };
     public static TestPackedTypes DefaultInstance {
@@ -16164,7 +16284,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestPackedTypes DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestPackedTypes ThisMessage {
@@ -16607,6 +16727,24 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestPackedTypes ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestPackedTypes MakeReadOnly() {
+      packedInt32_.MakeReadOnly();
+      packedInt64_.MakeReadOnly();
+      packedUint32_.MakeReadOnly();
+      packedUint64_.MakeReadOnly();
+      packedSint32_.MakeReadOnly();
+      packedSint64_.MakeReadOnly();
+      packedFixed32_.MakeReadOnly();
+      packedFixed64_.MakeReadOnly();
+      packedSfixed32_.MakeReadOnly();
+      packedSfixed64_.MakeReadOnly();
+      packedFloat_.MakeReadOnly();
+      packedDouble_.MakeReadOnly();
+      packedBool_.MakeReadOnly();
+      packedEnum_.MakeReadOnly();
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -16622,22 +16760,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestPackedTypes();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestPackedTypes cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestPackedTypes result;
+      private bool resultIsReadOnly;
+      private TestPackedTypes result;
       
       private TestPackedTypes PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestPackedTypes original = result;
           result = new TestPackedTypes();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -16652,13 +16790,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestPackedTypes();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -16674,25 +16812,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestPackedTypes BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        result.packedInt32_.MakeReadOnly();
-        result.packedInt64_.MakeReadOnly();
-        result.packedUint32_.MakeReadOnly();
-        result.packedUint64_.MakeReadOnly();
-        result.packedSint32_.MakeReadOnly();
-        result.packedSint64_.MakeReadOnly();
-        result.packedFixed32_.MakeReadOnly();
-        result.packedFixed64_.MakeReadOnly();
-        result.packedSfixed32_.MakeReadOnly();
-        result.packedSfixed64_.MakeReadOnly();
-        result.packedFloat_.MakeReadOnly();
-        result.packedDouble_.MakeReadOnly();
-        result.packedBool_.MakeReadOnly();
-        result.packedEnum_.MakeReadOnly();
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -17330,7 +17454,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestUnpackedTypes : pb::GeneratedMessage<TestUnpackedTypes, TestUnpackedTypes.Builder> {
-    private static readonly TestUnpackedTypes defaultInstance = new Builder().BuildPartial();
+    private static readonly TestUnpackedTypes defaultInstance = new TestUnpackedTypes().MakeReadOnly();
     private static readonly string[] _testUnpackedTypesFieldNames = new string[] { "unpacked_bool", "unpacked_double", "unpacked_enum", "unpacked_fixed32", "unpacked_fixed64", "unpacked_float", "unpacked_int32", "unpacked_int64", "unpacked_sfixed32", "unpacked_sfixed64", "unpacked_sint32", "unpacked_sint64", "unpacked_uint32", "unpacked_uint64" };
     private static readonly uint[] _testUnpackedTypesFieldTags = new uint[] { 816, 809, 824, 773, 777, 805, 720, 728, 789, 793, 752, 760, 736, 744 };
     public static TestUnpackedTypes DefaultInstance {
@@ -17338,7 +17462,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestUnpackedTypes DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestUnpackedTypes ThisMessage {
@@ -17726,6 +17850,24 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestUnpackedTypes ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestUnpackedTypes MakeReadOnly() {
+      unpackedInt32_.MakeReadOnly();
+      unpackedInt64_.MakeReadOnly();
+      unpackedUint32_.MakeReadOnly();
+      unpackedUint64_.MakeReadOnly();
+      unpackedSint32_.MakeReadOnly();
+      unpackedSint64_.MakeReadOnly();
+      unpackedFixed32_.MakeReadOnly();
+      unpackedFixed64_.MakeReadOnly();
+      unpackedSfixed32_.MakeReadOnly();
+      unpackedSfixed64_.MakeReadOnly();
+      unpackedFloat_.MakeReadOnly();
+      unpackedDouble_.MakeReadOnly();
+      unpackedBool_.MakeReadOnly();
+      unpackedEnum_.MakeReadOnly();
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -17741,22 +17883,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestUnpackedTypes();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestUnpackedTypes cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestUnpackedTypes result;
+      private bool resultIsReadOnly;
+      private TestUnpackedTypes result;
       
       private TestUnpackedTypes PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestUnpackedTypes original = result;
           result = new TestUnpackedTypes();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -17771,13 +17913,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestUnpackedTypes();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -17793,25 +17935,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestUnpackedTypes BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        result.unpackedInt32_.MakeReadOnly();
-        result.unpackedInt64_.MakeReadOnly();
-        result.unpackedUint32_.MakeReadOnly();
-        result.unpackedUint64_.MakeReadOnly();
-        result.unpackedSint32_.MakeReadOnly();
-        result.unpackedSint64_.MakeReadOnly();
-        result.unpackedFixed32_.MakeReadOnly();
-        result.unpackedFixed64_.MakeReadOnly();
-        result.unpackedSfixed32_.MakeReadOnly();
-        result.unpackedSfixed64_.MakeReadOnly();
-        result.unpackedFloat_.MakeReadOnly();
-        result.unpackedDouble_.MakeReadOnly();
-        result.unpackedBool_.MakeReadOnly();
-        result.unpackedEnum_.MakeReadOnly();
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -18449,7 +18577,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestPackedExtensions : pb::ExtendableMessage<TestPackedExtensions, TestPackedExtensions.Builder> {
-    private static readonly TestPackedExtensions defaultInstance = new Builder().BuildPartial();
+    private static readonly TestPackedExtensions defaultInstance = new TestPackedExtensions().MakeReadOnly();
     private static readonly string[] _testPackedExtensionsFieldNames = new string[] {  };
     private static readonly uint[] _testPackedExtensionsFieldTags = new uint[] {  };
     public static TestPackedExtensions DefaultInstance {
@@ -18457,7 +18585,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestPackedExtensions DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestPackedExtensions ThisMessage {
@@ -18531,6 +18659,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestPackedExtensions ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestPackedExtensions MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -18546,22 +18678,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestPackedExtensions();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestPackedExtensions cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestPackedExtensions result;
+      private bool resultIsReadOnly;
+      private TestPackedExtensions result;
       
       private TestPackedExtensions PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestPackedExtensions original = result;
           result = new TestPackedExtensions();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -18576,13 +18708,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestPackedExtensions();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -18598,11 +18730,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestPackedExtensions BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -18680,7 +18812,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestUnpackedExtensions : pb::ExtendableMessage<TestUnpackedExtensions, TestUnpackedExtensions.Builder> {
-    private static readonly TestUnpackedExtensions defaultInstance = new Builder().BuildPartial();
+    private static readonly TestUnpackedExtensions defaultInstance = new TestUnpackedExtensions().MakeReadOnly();
     private static readonly string[] _testUnpackedExtensionsFieldNames = new string[] {  };
     private static readonly uint[] _testUnpackedExtensionsFieldTags = new uint[] {  };
     public static TestUnpackedExtensions DefaultInstance {
@@ -18688,7 +18820,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestUnpackedExtensions DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestUnpackedExtensions ThisMessage {
@@ -18762,6 +18894,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestUnpackedExtensions ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestUnpackedExtensions MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -18777,22 +18913,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestUnpackedExtensions();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestUnpackedExtensions cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestUnpackedExtensions result;
+      private bool resultIsReadOnly;
+      private TestUnpackedExtensions result;
       
       private TestUnpackedExtensions PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestUnpackedExtensions original = result;
           result = new TestUnpackedExtensions();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -18807,13 +18943,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestUnpackedExtensions();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -18829,11 +18965,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestUnpackedExtensions BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -18911,7 +19047,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestDynamicExtensions : pb::GeneratedMessage<TestDynamicExtensions, TestDynamicExtensions.Builder> {
-    private static readonly TestDynamicExtensions defaultInstance = new Builder().BuildPartial();
+    private static readonly TestDynamicExtensions defaultInstance = new TestDynamicExtensions().MakeReadOnly();
     private static readonly string[] _testDynamicExtensionsFieldNames = new string[] { "dynamic_enum_extension", "dynamic_message_extension", "enum_extension", "message_extension", "packed_extension", "repeated_extension", "scalar_extension" };
     private static readonly uint[] _testDynamicExtensionsFieldTags = new uint[] { 16016, 16034, 16008, 16026, 16050, 16042, 16005 };
     public static TestDynamicExtensions DefaultInstance {
@@ -18919,7 +19055,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestDynamicExtensions DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestDynamicExtensions ThisMessage {
@@ -18951,7 +19087,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
       [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
       public sealed partial class DynamicMessageType : pb::GeneratedMessage<DynamicMessageType, DynamicMessageType.Builder> {
-        private static readonly DynamicMessageType defaultInstance = new Builder().BuildPartial();
+        private static readonly DynamicMessageType defaultInstance = new DynamicMessageType().MakeReadOnly();
         private static readonly string[] _dynamicMessageTypeFieldNames = new string[] { "dynamic_field" };
         private static readonly uint[] _dynamicMessageTypeFieldTags = new uint[] { 16800 };
         public static DynamicMessageType DefaultInstance {
@@ -18959,7 +19095,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public override DynamicMessageType DefaultInstanceForType {
-          get { return defaultInstance; }
+          get { return DefaultInstance; }
         }
         
         protected override DynamicMessageType ThisMessage {
@@ -19045,6 +19181,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         public static DynamicMessageType ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
+        private DynamicMessageType MakeReadOnly() {
+          return this;
+        }
+        
         public static Builder CreateBuilder() { return new Builder(); }
         public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
@@ -19060,22 +19200,22 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return this; }
           }
           public Builder() {
-            result = DefaultInstance ?? new DynamicMessageType();
-            builderIsReadOnly = result == DefaultInstance;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
           }
           internal Builder(DynamicMessageType cloneFrom) {
             result = cloneFrom;
-            builderIsReadOnly = true;
+            resultIsReadOnly = true;
           }
           
-          bool builderIsReadOnly;
-          DynamicMessageType result;
+          private bool resultIsReadOnly;
+          private DynamicMessageType result;
           
           private DynamicMessageType PrepareBuilder() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               DynamicMessageType original = result;
               result = new DynamicMessageType();
-              builderIsReadOnly = false;
+              resultIsReadOnly = false;
               MergeFrom(original);
             }
             return result;
@@ -19090,13 +19230,13 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override Builder Clear() {
-            result = DefaultInstance ?? new DynamicMessageType();
-            builderIsReadOnly = true;
+            result = DefaultInstance;
+            resultIsReadOnly = true;
             return this;
           }
           
           public override Builder Clone() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return new Builder(result);
             } else {
               return new Builder().MergeFrom(result);
@@ -19112,11 +19252,11 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override DynamicMessageType BuildPartial() {
-            if (builderIsReadOnly) {
+            if (resultIsReadOnly) {
               return result;
             }
-            builderIsReadOnly = true;
-            return result;
+            resultIsReadOnly = true;
+            return result.MakeReadOnly();
           }
           
           public override Builder MergeFrom(pb::IMessage other) {
@@ -19252,22 +19392,22 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     public const int MessageExtensionFieldNumber = 2003;
     private bool hasMessageExtension;
-    private global::Google.ProtocolBuffers.TestProtos.ForeignMessage messageExtension_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.ForeignMessage messageExtension_;
     public bool HasMessageExtension {
       get { return hasMessageExtension; }
     }
     public global::Google.ProtocolBuffers.TestProtos.ForeignMessage MessageExtension {
-      get { return messageExtension_; }
+      get { return messageExtension_ ?? global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance; }
     }
     
     public const int DynamicMessageExtensionFieldNumber = 2004;
     private bool hasDynamicMessageExtension;
-    private global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType dynamicMessageExtension_ = global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType.DefaultInstance;
+    private global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType dynamicMessageExtension_;
     public bool HasDynamicMessageExtension {
       get { return hasDynamicMessageExtension; }
     }
     public global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType DynamicMessageExtension {
-      get { return dynamicMessageExtension_; }
+      get { return dynamicMessageExtension_ ?? global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType.DefaultInstance; }
     }
     
     public const int RepeatedExtensionFieldNumber = 2005;
@@ -19405,6 +19545,12 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestDynamicExtensions ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestDynamicExtensions MakeReadOnly() {
+      repeatedExtension_.MakeReadOnly();
+      packedExtension_.MakeReadOnly();
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -19420,22 +19566,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestDynamicExtensions();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestDynamicExtensions cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestDynamicExtensions result;
+      private bool resultIsReadOnly;
+      private TestDynamicExtensions result;
       
       private TestDynamicExtensions PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestDynamicExtensions original = result;
           result = new TestDynamicExtensions();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -19450,13 +19596,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestDynamicExtensions();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -19472,13 +19618,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestDynamicExtensions BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        result.repeatedExtension_.MakeReadOnly();
-        result.packedExtension_.MakeReadOnly();
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -19720,7 +19864,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearMessageExtension() {
         PrepareBuilder();
         result.hasMessageExtension = false;
-        result.messageExtension_ = global::Google.ProtocolBuffers.TestProtos.ForeignMessage.DefaultInstance;
+        result.messageExtension_ = null;
         return this;
       }
       
@@ -19760,7 +19904,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public Builder ClearDynamicMessageExtension() {
         PrepareBuilder();
         result.hasDynamicMessageExtension = false;
-        result.dynamicMessageExtension_ = global::Google.ProtocolBuffers.TestProtos.TestDynamicExtensions.Types.DynamicMessageType.DefaultInstance;
+        result.dynamicMessageExtension_ = null;
         return this;
       }
       
@@ -19835,7 +19979,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class TestRepeatedScalarDifferentTagSizes : pb::GeneratedMessage<TestRepeatedScalarDifferentTagSizes, TestRepeatedScalarDifferentTagSizes.Builder> {
-    private static readonly TestRepeatedScalarDifferentTagSizes defaultInstance = new Builder().BuildPartial();
+    private static readonly TestRepeatedScalarDifferentTagSizes defaultInstance = new TestRepeatedScalarDifferentTagSizes().MakeReadOnly();
     private static readonly string[] _testRepeatedScalarDifferentTagSizesFieldNames = new string[] { "repeated_fixed32", "repeated_fixed64", "repeated_float", "repeated_int32", "repeated_int64", "repeated_uint64" };
     private static readonly uint[] _testRepeatedScalarDifferentTagSizesFieldTags = new uint[] { 101, 16369, 2097141, 104, 16376, 2097144 };
     public static TestRepeatedScalarDifferentTagSizes DefaultInstance {
@@ -19843,7 +19987,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override TestRepeatedScalarDifferentTagSizes DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override TestRepeatedScalarDifferentTagSizes ThisMessage {
@@ -20051,6 +20195,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static TestRepeatedScalarDifferentTagSizes ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private TestRepeatedScalarDifferentTagSizes MakeReadOnly() {
+      repeatedFixed32_.MakeReadOnly();
+      repeatedInt32_.MakeReadOnly();
+      repeatedFixed64_.MakeReadOnly();
+      repeatedInt64_.MakeReadOnly();
+      repeatedFloat_.MakeReadOnly();
+      repeatedUint64_.MakeReadOnly();
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -20066,22 +20220,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new TestRepeatedScalarDifferentTagSizes();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(TestRepeatedScalarDifferentTagSizes cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      TestRepeatedScalarDifferentTagSizes result;
+      private bool resultIsReadOnly;
+      private TestRepeatedScalarDifferentTagSizes result;
       
       private TestRepeatedScalarDifferentTagSizes PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           TestRepeatedScalarDifferentTagSizes original = result;
           result = new TestRepeatedScalarDifferentTagSizes();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -20096,13 +20250,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new TestRepeatedScalarDifferentTagSizes();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -20118,17 +20272,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override TestRepeatedScalarDifferentTagSizes BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        result.repeatedFixed32_.MakeReadOnly();
-        result.repeatedInt32_.MakeReadOnly();
-        result.repeatedFixed64_.MakeReadOnly();
-        result.repeatedInt64_.MakeReadOnly();
-        result.repeatedFloat_.MakeReadOnly();
-        result.repeatedUint64_.MakeReadOnly();
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -20448,7 +20596,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class FooRequest : pb::GeneratedMessage<FooRequest, FooRequest.Builder> {
-    private static readonly FooRequest defaultInstance = new Builder().BuildPartial();
+    private static readonly FooRequest defaultInstance = new FooRequest().MakeReadOnly();
     private static readonly string[] _fooRequestFieldNames = new string[] {  };
     private static readonly uint[] _fooRequestFieldTags = new uint[] {  };
     public static FooRequest DefaultInstance {
@@ -20456,7 +20604,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override FooRequest DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override FooRequest ThisMessage {
@@ -20526,6 +20674,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static FooRequest ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private FooRequest MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -20541,22 +20693,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new FooRequest();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(FooRequest cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      FooRequest result;
+      private bool resultIsReadOnly;
+      private FooRequest result;
       
       private FooRequest PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           FooRequest original = result;
           result = new FooRequest();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -20571,13 +20723,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new FooRequest();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -20593,11 +20745,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override FooRequest BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -20674,7 +20826,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class FooResponse : pb::GeneratedMessage<FooResponse, FooResponse.Builder> {
-    private static readonly FooResponse defaultInstance = new Builder().BuildPartial();
+    private static readonly FooResponse defaultInstance = new FooResponse().MakeReadOnly();
     private static readonly string[] _fooResponseFieldNames = new string[] {  };
     private static readonly uint[] _fooResponseFieldTags = new uint[] {  };
     public static FooResponse DefaultInstance {
@@ -20682,7 +20834,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override FooResponse DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override FooResponse ThisMessage {
@@ -20752,6 +20904,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static FooResponse ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private FooResponse MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -20767,22 +20923,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new FooResponse();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(FooResponse cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      FooResponse result;
+      private bool resultIsReadOnly;
+      private FooResponse result;
       
       private FooResponse PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           FooResponse original = result;
           result = new FooResponse();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -20797,13 +20953,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new FooResponse();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -20819,11 +20975,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override FooResponse BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -20900,7 +21056,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class BarRequest : pb::GeneratedMessage<BarRequest, BarRequest.Builder> {
-    private static readonly BarRequest defaultInstance = new Builder().BuildPartial();
+    private static readonly BarRequest defaultInstance = new BarRequest().MakeReadOnly();
     private static readonly string[] _barRequestFieldNames = new string[] {  };
     private static readonly uint[] _barRequestFieldTags = new uint[] {  };
     public static BarRequest DefaultInstance {
@@ -20908,7 +21064,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override BarRequest DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override BarRequest ThisMessage {
@@ -20978,6 +21134,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static BarRequest ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private BarRequest MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -20993,22 +21153,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new BarRequest();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(BarRequest cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      BarRequest result;
+      private bool resultIsReadOnly;
+      private BarRequest result;
       
       private BarRequest PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           BarRequest original = result;
           result = new BarRequest();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -21023,13 +21183,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new BarRequest();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -21045,11 +21205,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override BarRequest BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
@@ -21126,7 +21286,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("ProtoGen", "2.3.0.277")]
   public sealed partial class BarResponse : pb::GeneratedMessage<BarResponse, BarResponse.Builder> {
-    private static readonly BarResponse defaultInstance = new Builder().BuildPartial();
+    private static readonly BarResponse defaultInstance = new BarResponse().MakeReadOnly();
     private static readonly string[] _barResponseFieldNames = new string[] {  };
     private static readonly uint[] _barResponseFieldTags = new uint[] {  };
     public static BarResponse DefaultInstance {
@@ -21134,7 +21294,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public override BarResponse DefaultInstanceForType {
-      get { return defaultInstance; }
+      get { return DefaultInstance; }
     }
     
     protected override BarResponse ThisMessage {
@@ -21204,6 +21364,10 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static BarResponse ParseFrom(pb::ICodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
+    private BarResponse MakeReadOnly() {
+      return this;
+    }
+    
     public static Builder CreateBuilder() { return new Builder(); }
     public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
@@ -21219,22 +21383,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return this; }
       }
       public Builder() {
-        result = DefaultInstance ?? new BarResponse();
-        builderIsReadOnly = result == DefaultInstance;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
       }
       internal Builder(BarResponse cloneFrom) {
         result = cloneFrom;
-        builderIsReadOnly = true;
+        resultIsReadOnly = true;
       }
       
-      bool builderIsReadOnly;
-      BarResponse result;
+      private bool resultIsReadOnly;
+      private BarResponse result;
       
       private BarResponse PrepareBuilder() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           BarResponse original = result;
           result = new BarResponse();
-          builderIsReadOnly = false;
+          resultIsReadOnly = false;
           MergeFrom(original);
         }
         return result;
@@ -21249,13 +21413,13 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override Builder Clear() {
-        result = DefaultInstance ?? new BarResponse();
-        builderIsReadOnly = true;
+        result = DefaultInstance;
+        resultIsReadOnly = true;
         return this;
       }
       
       public override Builder Clone() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return new Builder(result);
         } else {
           return new Builder().MergeFrom(result);
@@ -21271,11 +21435,11 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override BarResponse BuildPartial() {
-        if (builderIsReadOnly) {
+        if (resultIsReadOnly) {
           return result;
         }
-        builderIsReadOnly = true;
-        return result;
+        resultIsReadOnly = true;
+        return result.MakeReadOnly();
       }
       
       public override Builder MergeFrom(pb::IMessage other) {
author	csharptest <roger@csharptest.net>	2011-09-23 11:14:01 -0500
committer	rogerk <devnull@localhost>	2011-09-23 11:14:01 -0500
commit	a314d4c9fa70c2b22bae02fa22a5dc2dba1db067 (patch)
tree	a8c75a9eff5bfff65ce537f65d529a7b8e93683d /src/ProtocolBuffersLite.Test
parent	dc24b605e356dbfda692e952807b404cccf245bc (diff)
download	protobuf-a314d4c9fa70c2b22bae02fa22a5dc2dba1db067.tar.gz protobuf-a314d4c9fa70c2b22bae02fa22a5dc2dba1db067.tar.bz2 protobuf-a314d4c9fa70c2b22bae02fa22a5dc2dba1db067.zip