The great generics revisiting.

csharp/ProtocolBuffers.Test/AbstractMessageTest.cs

@@ -10,15 +10,13 @@ namespace Google.ProtocolBuffers {
 
     [Test]
     public void Clear() {
-      AbstractMessageWrapper message = (AbstractMessageWrapper)
-        new AbstractMessageWrapper.Builder(TestAllTypes.CreateBuilder(TestUtil.GetAllSet())).Clear().Build();
+      AbstractMessageWrapper message = new AbstractMessageWrapper.Builder(TestAllTypes.CreateBuilder(TestUtil.GetAllSet())).Clear().Build();
       TestUtil.AssertClear((TestAllTypes) message.WrappedMessage);
     }
 
     [Test]
     public void Copy() {
-      AbstractMessageWrapper message = (AbstractMessageWrapper)
-        new AbstractMessageWrapper.Builder(TestAllTypes.CreateBuilder()).MergeFrom(TestUtil.GetAllSet()).Build();
+      AbstractMessageWrapper message = new AbstractMessageWrapper.Builder(TestAllTypes.CreateBuilder()).MergeFrom(TestUtil.GetAllSet()).Build();
       TestUtil.AssertAllFieldsSet((TestAllTypes) message.WrappedMessage);
     }
 
@@ -40,7 +38,7 @@ namespace Google.ProtocolBuffers {
     [Test]
     public void Parsing() {
       IBuilder builder = new AbstractMessageWrapper.Builder(TestAllTypes.CreateBuilder());
-      AbstractMessageWrapper message = (AbstractMessageWrapper) builder.MergeFrom(TestUtil.GetAllSet().ToByteString()).Build();
+      AbstractMessageWrapper message = (AbstractMessageWrapper) builder.WeakMergeFrom(TestUtil.GetAllSet().ToByteString()).WeakBuild();
       TestUtil.AssertAllFieldsSet((TestAllTypes) message.WrappedMessage);
     }
 
@@ -177,7 +175,7 @@ namespace Google.ProtocolBuffers {
       Assert.AreEqual(message, message);
       
       // Object should be equal to a dynamic copy of itself.
-      DynamicMessage dynamic = (DynamicMessage) ((IBuilder) DynamicMessage.CreateBuilder(message)).Build();
+      DynamicMessage dynamic = DynamicMessage.CreateBuilder(message).Build();
       Assert.AreEqual(message, dynamic);
       Assert.AreEqual(dynamic, message);
       Assert.AreEqual(dynamic.GetHashCode(), message.GetHashCode());
@@ -207,7 +205,7 @@ namespace Google.ProtocolBuffers {
     /// test that AbstractMessage's implementations work even if the wrapped
     /// object does not use them.
     /// </summary>
-    private class AbstractMessageWrapper : AbstractMessage {
+    private class AbstractMessageWrapper : AbstractMessage<AbstractMessageWrapper, AbstractMessageWrapper.Builder> {
       private readonly IMessage wrappedMessage;
 
       public IMessage WrappedMessage {
@@ -222,8 +220,8 @@ namespace Google.ProtocolBuffers {
         get { return wrappedMessage.DescriptorForType; }
       }
 
-      protected override IMessage DefaultInstanceForTypeImpl {
-        get { return new AbstractMessageWrapper(wrappedMessage.DefaultInstanceForType); }
+      public override AbstractMessageWrapper DefaultInstanceForType {
+        get { return new AbstractMessageWrapper(wrappedMessage.WeakDefaultInstanceForType); }
       }
 
       public override IDictionary<FieldDescriptor, object> AllFields {
@@ -250,17 +248,26 @@ namespace Google.ProtocolBuffers {
         get { return wrappedMessage.UnknownFields; }
       }
 
-      protected override IBuilder CreateBuilderForTypeImpl() {
-        return new Builder(wrappedMessage.CreateBuilderForType());
+      public override Builder CreateBuilderForType() {
+        return new Builder(wrappedMessage.WeakCreateBuilderForType());
       }
 
-      internal class Builder : AbstractBuilder {
+      internal class Builder : AbstractBuilder<AbstractMessageWrapper, Builder> {
         private readonly IBuilder wrappedBuilder;
 
+        protected override Builder ThisBuilder {
+          get { return this; }
+        }
+
         internal Builder(IBuilder wrappedBuilder) {
           this.wrappedBuilder = wrappedBuilder;
         }
 
+        public override Builder MergeFrom(AbstractMessageWrapper other) {
+          wrappedBuilder.WeakMergeFrom(other.wrappedMessage);
+          return this;
+        }
+
         public override bool IsInitialized {
           get { return wrappedBuilder.IsInitialized; }
         }
@@ -296,29 +303,29 @@ namespace Google.ProtocolBuffers {
           set { wrappedBuilder.UnknownFields = value; }
         }
 
-        protected override IMessage BuildImpl() {
-          return new AbstractMessageWrapper(wrappedBuilder.Build());
+        public override AbstractMessageWrapper Build() {
+          return new AbstractMessageWrapper(wrappedBuilder.WeakBuild());
         }
 
-        protected override IMessage BuildPartialImpl() {
-          return new AbstractMessageWrapper(wrappedBuilder.BuildPartial());
+        public override AbstractMessageWrapper BuildPartial() {
+          return new AbstractMessageWrapper(wrappedBuilder.WeakBuildPartial());
         }
 
-        protected override IBuilder CloneImpl() {
-          return new Builder(wrappedBuilder.Clone());
+        public override Builder Clone() {
+          return new Builder(wrappedBuilder.WeakClone());
         }
 
-        protected override IMessage DefaultInstanceForTypeImpl {
-          get { return wrappedBuilder.DefaultInstanceForType; }
+        public override AbstractMessageWrapper DefaultInstanceForType {
+          get { return new AbstractMessageWrapper(wrappedBuilder.WeakDefaultInstanceForType); }
         }
 
-        protected override IBuilder ClearFieldImpl(FieldDescriptor field) {
-          wrappedBuilder.ClearField(field);
+        public override Builder ClearField(FieldDescriptor field) {
+          wrappedBuilder.WeakClearField(field);
           return this;
         }
 
-        protected override IBuilder AddRepeatedFieldImpl(FieldDescriptor field, object value) {
-          wrappedBuilder.AddRepeatedField(field, value);
+        public override Builder AddRepeatedField(FieldDescriptor field, object value) {
+          wrappedBuilder.WeakAddRepeatedField(field, value);
           return this;
         }
 
@@ -327,13 +334,13 @@ namespace Google.ProtocolBuffers {
           return this;
         }
 
-        public override IBuilder MergeFrom(IMessage other) {
-          wrappedBuilder.MergeFrom(other);
+        public override Builder MergeFrom(IMessage other) {
+          wrappedBuilder.WeakMergeFrom(other);
           return this;
         }
 
-        protected override IBuilder MergeFromImpl(CodedInputStream input, ExtensionRegistry extensionRegistry) {
-          wrappedBuilder.MergeFrom(input, extensionRegistry);
+        public override Builder MergeFrom(CodedInputStream input, ExtensionRegistry extensionRegistry) {
+          wrappedBuilder.WeakMergeFrom(input, extensionRegistry);
           return this;
         }
       }

csharp/ProtocolBuffers.Test/DynamicMessageTest.cs

@@ -21,7 +21,7 @@ namespace Google.ProtocolBuffers {
     public void DynamicMessageAccessors() {
       IBuilder builder = DynamicMessage.CreateBuilder(TestAllTypes.Descriptor);
       reflectionTester.SetAllFieldsViaReflection(builder);
-      IMessage message = builder.Build();
+      IMessage message = builder.WeakBuild();
       reflectionTester.AssertAllFieldsSetViaReflection(message);
     }
 
@@ -32,7 +32,7 @@ namespace Google.ProtocolBuffers {
     // It treats them just like any other fields.
     IBuilder builder = DynamicMessage.CreateBuilder(TestAllExtensions.Descriptor);
     extensionsReflectionTester.SetAllFieldsViaReflection(builder);
-    IMessage message = builder.Build();
+    IMessage message = builder.WeakBuild();
     extensionsReflectionTester.AssertAllFieldsSetViaReflection(message);
   }
 
@@ -41,7 +41,7 @@ namespace Google.ProtocolBuffers {
       IBuilder builder = DynamicMessage.CreateBuilder(TestAllTypes.Descriptor);
       reflectionTester.SetAllFieldsViaReflection(builder);
       reflectionTester.ModifyRepeatedFieldsViaReflection(builder);
-      IMessage message = builder.Build();
+      IMessage message = builder.WeakBuild();
       reflectionTester.AssertRepeatedFieldsModifiedViaReflection(message);
     }
 
@@ -57,7 +57,7 @@ namespace Google.ProtocolBuffers {
 
       IBuilder dynamicBuilder = DynamicMessage.CreateBuilder(TestAllTypes.Descriptor);
       reflectionTester.SetAllFieldsViaReflection(dynamicBuilder);
-      IMessage dynamicMessage = dynamicBuilder.Build();
+      IMessage dynamicMessage = dynamicBuilder.WeakBuild();
 
       Assert.AreEqual(message.SerializedSize, dynamicMessage.SerializedSize);
     }
@@ -66,7 +66,7 @@ namespace Google.ProtocolBuffers {
     public void DynamicMessageSerialization() {
       IBuilder builder =  DynamicMessage.CreateBuilder(TestAllTypes.Descriptor);
       reflectionTester.SetAllFieldsViaReflection(builder);
-      IMessage message = builder.Build();
+      IMessage message = builder.WeakBuild();
 
       ByteString rawBytes = message.ToByteString();
       TestAllTypes message2 = TestAllTypes.ParseFrom(rawBytes);

csharp/ProtocolBuffers.Test/MessageTest.cs

@@ -153,8 +153,7 @@ namespace Google.ProtocolBuffers {
       builder[descriptor.FindDescriptor<FieldDescriptor>("optional_message")] = TestRequiredInitialized;
       Assert.IsTrue(builder.IsInitialized);
 
-      // TODO(jonskeet): Remove this nastiness by making IBuilder always generic.
-      ((IBuilder) builder).AddRepeatedField(descriptor.FindDescriptor<FieldDescriptor>("repeated_message"), TestRequiredUninitialized);
+      builder.AddRepeatedField(descriptor.FindDescriptor<FieldDescriptor>("repeated_message"), TestRequiredUninitialized);
       Assert.IsFalse(builder.IsInitialized);
 
       builder.SetRepeatedField(descriptor.FindDescriptor<FieldDescriptor>("repeated_message"), 0, TestRequiredInitialized);
@@ -266,8 +265,7 @@ namespace Google.ProtocolBuffers {
     [Test]
     public void DynamicBuildPartial() {
       // We're mostly testing that no exception is thrown.
-      // TODO(jonskeet): Fix this ghastly casting mess
-      DynamicMessage message = (DynamicMessage) ((IBuilder) DynamicMessage.CreateBuilder(TestRequired.Descriptor)).BuildPartial();
+      DynamicMessage message = DynamicMessage.CreateBuilder(TestRequired.Descriptor).BuildPartial();
       Assert.IsFalse(message.Initialized);
     }
 

csharp/ProtocolBuffers.Test/TestProtos/MessageWithNoOuter.cs

@@ -95,12 +95,16 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public static Builder CreateBuilder() { return new Builder(); }
-        public override IBuilder<self::MessageWithNoOuter.Types.NestedMessage> CreateBuilderForType() { return new Builder(); }
+        public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(self::MessageWithNoOuter.Types.NestedMessage prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
         }
         
         public sealed partial class Builder : pb::GeneratedBuilder<self::MessageWithNoOuter.Types.NestedMessage, Builder> {
+          protected override Builder ThisBuilder {
+            get { return this; }
+          }
+          
           // Construct using self::MessageWithNoOuter.Types.NestedMessage.CreateBuilder()
           internal Builder() {}
           
@@ -110,12 +114,12 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return result; }
           }
           
-          public override IBuilder<self::MessageWithNoOuter.Types.NestedMessage> Clear() {
+          public override Builder Clear() {
             result = new self::MessageWithNoOuter.Types.NestedMessage();
             return this;
           }
           
-          public override IBuilder<self::MessageWithNoOuter.Types.NestedMessage> Clone() {
+          public override Builder Clone() {
             return new Builder().MergeFrom(result);
           }
           
@@ -231,12 +235,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::MessageWithNoOuter> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::MessageWithNoOuter prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::MessageWithNoOuter, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::MessageWithNoOuter.CreateBuilder()
       internal Builder() {}
       
@@ -246,12 +254,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::MessageWithNoOuter> Clear() {
+      public override Builder Clear() {
         result = new self::MessageWithNoOuter();
         return this;
       }
       
-      public override IBuilder<self::MessageWithNoOuter> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       

csharp/ProtocolBuffers.Test/TestProtos/MultiFileProto.cs

@@ -59,8 +59,8 @@ namespace Google.ProtocolBuffers.TestProtos {
     #endregion
     
     #region Extensions
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, int> ExtensionWithOuter =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[0]);
+    public static readonly pb::GeneratedExtensionBase<int> ExtensionWithOuter =
+          pb::GeneratedSingleExtension<int>.CreateInstance(Descriptor.Extensions[0]);
     #endregion
     
     #region Static variables

csharp/ProtocolBuffers.Test/TestProtos/ServiceWithNoOuter.cs

@@ -95,7 +95,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           controller,
           request,
           self::TestAllTypes.DefaultInstance,
-          pb::RpcUtil.GeneralizeCallback(done, self::TestAllTypes.DefaultInstance));
+          pb::RpcUtil.GeneralizeCallback<self::TestAllTypes, self::TestAllTypes.Builder>(done, self::TestAllTypes.DefaultInstance));
       }
     }
   }

csharp/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs

@@ -174,12 +174,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestEmbedOptimizedForSize> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestEmbedOptimizedForSize prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestEmbedOptimizedForSize, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestEmbedOptimizedForSize.CreateBuilder()
       internal Builder() {}
       
@@ -189,12 +193,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestEmbedOptimizedForSize> Clear() {
+      public override Builder Clear() {
         result = new self::TestEmbedOptimizedForSize();
         return this;
       }
       
-      public override IBuilder<self::TestEmbedOptimizedForSize> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -215,11 +219,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestEmbedOptimizedForSize) {
           return MergeFrom((self::TestEmbedOptimizedForSize) other);
         } else {
@@ -228,7 +228,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestEmbedOptimizedForSize> MergeFrom(self::TestEmbedOptimizedForSize other) {
+      public override Builder MergeFrom(self::TestEmbedOptimizedForSize other) {
         if (other == self::TestEmbedOptimizedForSize.DefaultInstance) return this;
         if (other.HasOptionalMessage) {
           MergeOptionalMessage(other.OptionalMessage);
@@ -243,11 +243,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestEmbedOptimizedForSize> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestEmbedOptimizedForSize> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {

csharp/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs

@@ -150,12 +150,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::ImportMessage> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::ImportMessage prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::ImportMessage, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::ImportMessage.CreateBuilder()
       internal Builder() {}
       
@@ -165,12 +169,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::ImportMessage> Clear() {
+      public override Builder Clear() {
         result = new self::ImportMessage();
         return this;
       }
       
-      public override IBuilder<self::ImportMessage> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -188,11 +192,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::ImportMessage) {
           return MergeFrom((self::ImportMessage) other);
         } else {
@@ -201,7 +201,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::ImportMessage> MergeFrom(self::ImportMessage other) {
+      public override Builder MergeFrom(self::ImportMessage other) {
         if (other == self::ImportMessage.DefaultInstance) return this;
         if (other.HasD) {
           D = other.D;
@@ -210,11 +210,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::ImportMessage> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::ImportMessage> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {

csharp/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs

@@ -77,8 +77,8 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     #region Nested types
     public static class Types {
-      public static readonly pb::GeneratedExtensionBase<self::TestOptimizedForSize, int> TestExtension =
-            pb::GeneratedSingleExtension<self::TestOptimizedForSize, int>.CreateInstance(Descriptor.Extensions[0]);
+      public static readonly pb::GeneratedExtensionBase<int> TestExtension =
+            pb::GeneratedSingleExtension<int>.CreateInstance(Descriptor.Extensions[0]);
     }
     #endregion
     
@@ -137,12 +137,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestOptimizedForSize> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestOptimizedForSize prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::ExtendableBuilder<self::TestOptimizedForSize, self::TestOptimizedForSize.Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestOptimizedForSize.CreateBuilder()
       internal Builder() {}
       
@@ -152,12 +156,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestOptimizedForSize> Clear() {
+      public override Builder Clear() {
         result = new self::TestOptimizedForSize();
         return this;
       }
       
-      public override IBuilder<self::TestOptimizedForSize> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       

csharp/ProtocolBuffers/AbstractMessage.cs

@@ -23,7 +23,9 @@ namespace Google.ProtocolBuffers {
   /// <summary>
   /// Implementation of the non-generic IMessage interface as far as possible.
   /// </summary>
-  public abstract class AbstractMessage : IMessage {
+  public abstract class AbstractMessage<TMessage, TBuilder> : IMessage<TMessage, TBuilder> 
+      where TMessage : AbstractMessage<TMessage, TBuilder> 
+      where TBuilder : AbstractBuilder<TMessage, TBuilder> {
     // TODO(jonskeet): Cleaner to use a Nullable<int>?
     /// <summary>
     /// The serialized size if it's already been computed, or -1
@@ -39,21 +41,17 @@ namespace Google.ProtocolBuffers {
     public abstract int GetRepeatedFieldCount(FieldDescriptor field);
     public abstract object this[FieldDescriptor field, int index] { get; }
     public abstract UnknownFieldSet UnknownFields { get; }
+    public abstract TMessage DefaultInstanceForType { get; }
+    public abstract TBuilder CreateBuilderForType();
     #endregion
-
-    #region New abstract methods to be overridden by implementations, allow explicit interface implementation
-    protected abstract IMessage DefaultInstanceForTypeImpl { get; }
-    protected abstract IBuilder CreateBuilderForTypeImpl();
-    #endregion
-
-    #region Methods simply proxying to the "Impl" methods, explicitly implementing IMessage
-    IMessage IMessage.DefaultInstanceForType { 
-      get { return DefaultInstanceForTypeImpl; }
+    
+    public IBuilder WeakCreateBuilderForType() {
+      return CreateBuilderForType();
     }
-    IBuilder IMessage.CreateBuilderForType() { 
-      return CreateBuilderForTypeImpl(); 
+
+    public IMessage WeakDefaultInstanceForType {
+      get { return DefaultInstanceForType; }
     }
-    #endregion
 
     public virtual bool IsInitialized {
       get {
@@ -71,7 +69,7 @@ namespace Google.ProtocolBuffers {
             if (field.IsRepeated) {
               // We know it's an IList<T>, but not the exact type - so
               // IEnumerable is the best we can do. (C# generics aren't covariant yet.)
-              foreach (IMessage element in (IEnumerable)entry.Value) {
+              foreach (IMessage element in (IEnumerable) entry.Value) {
                 if (!element.IsInitialized) {
                   return false;
                 }
@@ -124,7 +122,7 @@ namespace Google.ProtocolBuffers {
         foreach (KeyValuePair<FieldDescriptor, object> entry in AllFields) {
           FieldDescriptor field = entry.Key;
           if (field.IsRepeated) {
-            foreach (object element in (IEnumerable)entry.Value) {
+            foreach (object element in (IEnumerable) entry.Value) {
               size += CodedOutputStream.ComputeFieldSize(field.FieldType, field.FieldNumber, element);
             }
           } else {

csharp/ProtocolBuffers/CodedInputStream.cs

@@ -224,7 +224,7 @@ namespace Google.ProtocolBuffers {
         throw InvalidProtocolBufferException.RecursionLimitExceeded();
       }
       ++recursionDepth;
-      builder.MergeFrom(this, extensionRegistry);
+      builder.WeakMergeFrom(this, extensionRegistry);
       CheckLastTagWas(WireFormat.MakeTag(fieldNumber, WireFormat.WireType.EndGroup));
       --recursionDepth;
     }
@@ -253,7 +253,7 @@ namespace Google.ProtocolBuffers {
       }
       int oldLimit = PushLimit(length);
       ++recursionDepth;
-      builder.MergeFrom(this, extensionRegistry);
+      builder.WeakMergeFrom(this, extensionRegistry);
       CheckLastTagWas(0);
       --recursionDepth;
       PopLimit(oldLimit);

csharp/ProtocolBuffers/ExtendableBuilder.cs

@@ -13,57 +13,55 @@ namespace Google.ProtocolBuffers {
     /// <summary>
     /// Checks if a singular extension is present
     /// </summary>
-    public bool HasExtension<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension) {
+    public bool HasExtension<TExtension>(GeneratedExtensionBase<TExtension> extension) {
       return MessageBeingBuilt.HasExtension(extension);
     }
 
     /// <summary>
     /// Returns the number of elements in a repeated extension.
     /// </summary>
-    public int GetExtensionCount<TExtension>(GeneratedExtensionBase<TMessage, IList<TExtension>> extension) {
+    public int GetExtensionCount<TExtension>(GeneratedExtensionBase<IList<TExtension>> extension) {
       return MessageBeingBuilt.GetExtensionCount(extension);
     }
 
     /// <summary>
     /// Returns the value of an extension.
     /// </summary>
-    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension) {
+    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<TExtension> extension) {
       return MessageBeingBuilt.GetExtension(extension);
     }
 
     /// <summary>
     /// Returns one element of a repeated extension.
     /// </summary>
-    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<TMessage, IList<TExtension>> extension, int index) {
+    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<IList<TExtension>> extension, int index) {
       return MessageBeingBuilt.GetExtension(extension, index);
     }
 
     /// <summary>
     /// Sets the value of an extension.
     /// </summary>
-    public ExtendableBuilder<TMessage, TBuilder> SetExtension<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension, TExtension value) {
+    public TBuilder SetExtension<TExtension>(GeneratedExtensionBase<TExtension> extension, TExtension value) {
       ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
       message.VerifyExtensionContainingType(extension);
       message.Extensions[extension.Descriptor] = extension.ToReflectionType(value);
-      return this;
+      return ThisBuilder;
     }
 
     /// <summary>
     /// Sets the value of one element of a repeated extension.
     /// </summary>
-    public ExtendableBuilder<TMessage, TBuilder> SetExtension<TExtension>(
-        GeneratedExtensionBase<TMessage, IList<TExtension>> extension, int index, TExtension value) {
+    public TBuilder SetExtension<TExtension>(GeneratedExtensionBase<IList<TExtension>> extension, int index, TExtension value) {
       ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
       message.VerifyExtensionContainingType(extension);
       message.Extensions[extension.Descriptor, index] = extension.SingularToReflectionType(value);
-      return this;
+      return ThisBuilder;
     }
 
     /// <summary>
     /// Appends a value to a repeated extension.
     /// </summary>
-    public ExtendableBuilder<TMessage, TBuilder> AddExtension<TExtension>(
-        GeneratedExtensionBase<TMessage, IList<TExtension>> extension, TExtension value) {
+    public ExtendableBuilder<TMessage, TBuilder> AddExtension<TExtension>(GeneratedExtensionBase<IList<TExtension>> extension, TExtension value) {
       ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
       message.VerifyExtensionContainingType(extension);
       message.Extensions.AddRepeatedField(extension.Descriptor, extension.SingularToReflectionType(value));
@@ -73,8 +71,7 @@ namespace Google.ProtocolBuffers {
     /// <summary>
     /// Clears an extension.
     /// </summary>
-    public ExtendableBuilder<TMessage, TBuilder> ClearExtension<TExtension>(
-        GeneratedExtensionBase<TMessage, TExtension> extension) {
+    public ExtendableBuilder<TMessage, TBuilder> ClearExtension<TExtension>(GeneratedExtensionBase<TExtension> extension) {
       ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
       message.VerifyExtensionContainingType(extension);
       message.Extensions.ClearField(extension.Descriptor);
@@ -121,23 +118,23 @@ namespace Google.ProtocolBuffers {
       }
     }
 
-    public override IBuilder<TMessage> ClearField(FieldDescriptor field) {
+    public override TBuilder ClearField(FieldDescriptor field) {
       if (field.IsExtension) {
         ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
         message.VerifyContainingType(field);
         message.Extensions.ClearField(field);
-        return this;
+        return ThisBuilder;
       } else {
         return base.ClearField(field);
       }
     }
 
-    public override IBuilder<TMessage> AddRepeatedField(FieldDescriptor field, object value) {
+    public override TBuilder AddRepeatedField(FieldDescriptor field, object value) {
       if (field.IsExtension) {
         ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
         message.VerifyContainingType(field); 
         message.Extensions.AddRepeatedField(field, value);
-        return this;
+        return ThisBuilder;
       } else {
         return base.AddRepeatedField(field, value);
       }

csharp/ProtocolBuffers/ExtendableMessage.cs

@@ -5,9 +5,9 @@ using Google.ProtocolBuffers.Descriptors;
 using Google.ProtocolBuffers.Collections;
 
 namespace Google.ProtocolBuffers {
-  public abstract class ExtendableMessage<TMessage,TBuilder> : GeneratedMessage<TMessage,TBuilder>
+  public abstract class ExtendableMessage<TMessage, TBuilder> : GeneratedMessage<TMessage, TBuilder>
     where TMessage : GeneratedMessage<TMessage, TBuilder>
-    where TBuilder : IBuilder<TMessage> {
+    where TBuilder : GeneratedBuilder<TMessage, TBuilder> {
 
     protected ExtendableMessage() {}
     private readonly FieldSet extensions = FieldSet.CreateFieldSet();
@@ -22,21 +22,21 @@ namespace Google.ProtocolBuffers {
     /// <summary>
     /// Checks if a singular extension is present.
     /// </summary>
-    public bool HasExtension<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension) {
+    public bool HasExtension<TExtension>(GeneratedExtensionBase<TExtension> extension) {
       return extensions.HasField(extension.Descriptor);
     }
 
     /// <summary>
     /// Returns the number of elements in a repeated extension.
     /// </summary>
-    public int GetExtensionCount<TExtension>(GeneratedExtensionBase<TMessage, IList<TExtension>> extension) {
+    public int GetExtensionCount<TExtension>(GeneratedExtensionBase<IList<TExtension>> extension) {
       return extensions.GetRepeatedFieldCount(extension.Descriptor);
     }
 
     /// <summary>
     /// Returns the value of an extension.
     /// </summary>
-    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension) {
+    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<TExtension> extension) {
       object value = extensions[extension.Descriptor];
       if (value == null) {
         return (TExtension) extension.MessageDefaultInstance;
@@ -48,7 +48,7 @@ namespace Google.ProtocolBuffers {
     /// <summary>
     /// Returns one element of a repeated extension.
     /// </summary>
-    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<TMessage, IList<TExtension>> extension, int index) {
+    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<IList<TExtension>> extension, int index) {
       return (TExtension) extension.SingularFromReflectionType(extensions[extension.Descriptor, index]);
     }
 
@@ -169,7 +169,7 @@ namespace Google.ProtocolBuffers {
       get { return extensions.SerializedSize; }
     }
 
-    internal void VerifyExtensionContainingType<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension) {
+    internal void VerifyExtensionContainingType<TExtension>(GeneratedExtensionBase<TExtension> extension) {
       if (extension.Descriptor.ContainingType != DescriptorForType) {
         // This can only happen if someone uses unchecked operations.
         throw new ArgumentException("Extension is for type \"" + extension.Descriptor.ContainingType.FullName

csharp/ProtocolBuffers/ExtensionRegistry.cs

@@ -88,8 +88,7 @@ namespace Google.ProtocolBuffers {
     /// <summary>
     /// Add an extension from a generated file to the registry.
     /// </summary>
-    public void Add<TContainer, TExtension> (GeneratedExtensionBase<TContainer, TExtension> extension) 
-        where TContainer : IMessage<TContainer> {
+    public void Add<TExtension> (GeneratedExtensionBase<TExtension> extension) {
       if (extension.Descriptor.MappedType == MappedType.Message) {
         Add(new ExtensionInfo(extension.Descriptor, extension.MessageDefaultInstance));
       } else {

csharp/ProtocolBuffers/FieldAccess/RepeatedMessageAccessor.cs

@@ -40,7 +40,7 @@ namespace Google.ProtocolBuffers.FieldAccess {
 
       // No... so let's create a builder of the right type, and merge the value in.
       IMessage message = (IMessage) value;
-      return CreateBuilder().MergeFrom(message).Build();
+      return CreateBuilder().WeakMergeFrom(message).WeakBuild();
     }
 
     public override void SetRepeated(IBuilder builder, int index, object value) {

csharp/ProtocolBuffers/FieldAccess/SingleMessageAccessor.cs

@@ -38,7 +38,7 @@ namespace Google.ProtocolBuffers.FieldAccess {
       
       // No... so let's create a builder of the right type, and merge the value in.
       IMessage message = (IMessage) value;
-      return CreateBuilder().MergeFrom(message).Build();
+      return CreateBuilder().WeakMergeFrom(message).WeakBuild();
     }
 
     public override void SetValue(IBuilder builder, object value) {

csharp/ProtocolBuffers/FieldSet.cs

@@ -154,19 +154,19 @@ namespace Google.ProtocolBuffers {
         case FieldType.Message: {
             IBuilder subBuilder;
             if (defaultFieldInstance != null) {
-              subBuilder = defaultFieldInstance.CreateBuilderForType();
+              subBuilder = defaultFieldInstance.WeakCreateBuilderForType();
             } else {
               subBuilder = builder.CreateBuilderForField(field);
             }
             if (!field.IsRepeated) {
-              subBuilder.MergeFrom((IMessage) builder[field]);
+              subBuilder.WeakMergeFrom((IMessage) builder[field]);
             }
             if (field.FieldType == FieldType.Group) {
               input.ReadGroup(field.FieldNumber, subBuilder, extensionRegistry);
             } else {
               input.ReadMessage(subBuilder, extensionRegistry);
             }
-            value = subBuilder.Build();
+            value = subBuilder.WeakBuild();
             break;
           }
         case FieldType.Enum: {
@@ -185,7 +185,7 @@ namespace Google.ProtocolBuffers {
           break;
       }
       if (field.IsRepeated) {
-        builder.AddRepeatedField(field, value);
+        builder.WeakAddRepeatedField(field, value);
       } else {
         builder[field] = value;
       } 
@@ -236,16 +236,16 @@ namespace Google.ProtocolBuffers {
             ExtensionInfo extension = extensionRegistry[type, typeId];
             if (extension != null) {
               field = extension.Descriptor;
-              subBuilder = extension.DefaultInstance.CreateBuilderForType();
+              subBuilder = extension.DefaultInstance.WeakCreateBuilderForType();
               IMessage originalMessage = (IMessage) builder[field];
               if (originalMessage != null) {
-                subBuilder.MergeFrom(originalMessage);
+                subBuilder.WeakMergeFrom(originalMessage);
               }
               if (rawBytes != null) {
                 // We already encountered the message.  Parse it now.
                 // TODO(jonskeet): Check this is okay. It's subtly different from the Java, as it doesn't create an input stream from rawBytes.
                 // In fact, why don't we just call MergeFrom(rawBytes)? And what about the extension registry?
-                subBuilder.MergeFrom(rawBytes.CreateCodedInput());
+                subBuilder.WeakMergeFrom(rawBytes.CreateCodedInput());
                 rawBytes = null;
               }
             } else {
@@ -286,7 +286,7 @@ namespace Google.ProtocolBuffers {
       input.CheckLastTagWas(WireFormat.MessageSetTag.ItemEnd);
 
       if (subBuilder != null) {
-        builder[field] = subBuilder.Build();
+        builder[field] = subBuilder.WeakBuild();
       }
     }
 
@@ -381,7 +381,7 @@ namespace Google.ProtocolBuffers {
     }
 
     /// <summary>
-    /// See <see cref="IBuilder.AddRepeatedField" />
+    /// See <see cref="IBuilder{TMessage, TBuilder}.AddRepeatedField" />
     /// </summary>
     internal void AddRepeatedField(FieldDescriptor field, object value) {
       if (!field.IsRepeated) {
@@ -449,7 +449,7 @@ namespace Google.ProtocolBuffers {
     }
 
     /// <summary>
-    /// See <see cref="IBuilder.ClearField" />
+    /// See <see cref="IBuilder{TMessage, TBuilder}.ClearField" />
     /// </summary>
     public void ClearField(FieldDescriptor field) {
       fields.Remove(field);
@@ -495,10 +495,10 @@ namespace Google.ProtocolBuffers {
           }
         } else if (field.MappedType == MappedType.Message && existingValue != null) {
           IMessage existingMessage = (IMessage)existingValue;
-          IMessage merged = existingMessage.CreateBuilderForType()
-              .MergeFrom(existingMessage)
-              .MergeFrom((IMessage)entry.Value)
-              .Build();
+          IMessage merged = existingMessage.WeakCreateBuilderForType()
+              .WeakMergeFrom(existingMessage)
+              .WeakMergeFrom((IMessage) entry.Value)
+              .WeakBuild();
           this[field] = merged;
         } else {
           this[field] = entry.Value;

csharp/ProtocolBuffers/GeneratedBuilder.cs

@@ -13,9 +13,9 @@ namespace Google.ProtocolBuffers {
   /// most of the IBuilder interface using reflection. Users can ignore this class
   /// as an implementation detail.
   /// </summary>
-  public abstract class GeneratedBuilder<TMessage, TBuilder> : AbstractBuilder, IBuilder<TMessage>
+  public abstract class GeneratedBuilder<TMessage, TBuilder> : AbstractBuilder<TMessage, TBuilder>
       where TMessage : GeneratedMessage <TMessage, TBuilder>
-      where TBuilder : GeneratedBuilder<TMessage, TBuilder>, IBuilder<TMessage> {
+      where TBuilder : GeneratedBuilder<TMessage, TBuilder> {
 
     /// <summary>
     /// Returns the message being built at the moment.
@@ -43,7 +43,7 @@ namespace Google.ProtocolBuffers {
           : MessageBeingBuilt[field];
       }
       set {
-        InternalFieldAccessors[field].SetValue(this, value);
+        InternalFieldAccessors[field].SetValue(ThisBuilder, value);
       }
     }
 
@@ -87,40 +87,16 @@ namespace Google.ProtocolBuffers {
       return MessageBeingBuilt.HasField(field);
     }
 
-    protected override IMessage BuildImpl() {
-      return Build();
-    }
-
-    protected override IMessage BuildPartialImpl() {
-      return BuildPartial();
-    }
-
-    protected override IBuilder CloneImpl() {
-      return Clone();
-    }
-
-    protected override IMessage DefaultInstanceForTypeImpl {
-      get { return DefaultInstanceForType; }
-    }
-
     public override IBuilder CreateBuilderForField(FieldDescriptor field) {
       return InternalFieldAccessors[field].CreateBuilder();
     }
 
-    protected override IBuilder ClearFieldImpl(FieldDescriptor field) {
-      return ClearField(field);
-    }
-
-    protected override IBuilder AddRepeatedFieldImpl(FieldDescriptor field, object value) {
-      return AddRepeatedField(field, value);
-    }
-
-    public virtual IBuilder<TMessage> ClearField(FieldDescriptor field) {
+    public override TBuilder ClearField(FieldDescriptor field) {
       InternalFieldAccessors[field].Clear(this);
-      return this;
+      return ThisBuilder;
     }
 
-    public virtual IBuilder<TMessage> MergeFrom(TMessage other) {
+    public override TBuilder MergeFrom(TMessage other) {
       if (other.DescriptorForType != InternalFieldAccessors.Descriptor) {
         throw new ArgumentException("Message type mismatch");
       }
@@ -135,77 +111,31 @@ namespace Google.ProtocolBuffers {
         } else if (field.MappedType == MappedType.Message && HasField(field)) {
           // Merge singular embedded messages
           IMessage oldValue = (IMessage)this[field];
-          this[field] = oldValue.CreateBuilderForType()
-              .MergeFrom(oldValue)
-              .MergeFrom((IMessage)entry.Value)
-              .BuildPartial();
+          this[field] = oldValue.WeakCreateBuilderForType()
+              .WeakMergeFrom(oldValue)
+              .WeakMergeFrom((IMessage)entry.Value)
+              .WeakBuildPartial();
         } else {
           // Just overwrite
           this[field] = entry.Value;
         }
       }
-      return this;
+      return ThisBuilder;
     }
 
-    public virtual IBuilder<TMessage> MergeUnknownFields(UnknownFieldSet unknownFields) {
+    public override TBuilder MergeUnknownFields(UnknownFieldSet unknownFields) {
       TMessage result = MessageBeingBuilt;
       result.SetUnknownFields(UnknownFieldSet.CreateBuilder(result.UnknownFields)
           .MergeFrom(unknownFields)
           .Build());
-      return this;
+      return ThisBuilder;
     }
 
-    public virtual IBuilder<TMessage> AddRepeatedField(FieldDescriptor field, object value) {
+    public override TBuilder AddRepeatedField(FieldDescriptor field, object value) {
       InternalFieldAccessors[field].AddRepeated(this, value);
-      return this;
-    }
-
-    public IBuilder<TMessage> MergeFrom(ByteString data) {
-      ((IBuilder) this).MergeFrom(data);
-      return this;
-    }
-
-    public IBuilder<TMessage> MergeFrom(ByteString data, ExtensionRegistry extensionRegistry) {
-      ((IBuilder) this).MergeFrom(data, extensionRegistry);
-      return this;
-    }
-
-    public IBuilder<TMessage> MergeFrom(byte[] data) {
-      ((IBuilder) this).MergeFrom(data);
-      return this;
-    }
-
-    public IBuilder<TMessage> MergeFrom(byte[] data, ExtensionRegistry extensionRegistry) {
-      ((IBuilder) this).MergeFrom(data, extensionRegistry);
-      return this;
-    }
-
-    public IBuilder<TMessage> MergeFrom(Stream input) {
-      ((IBuilder) this).MergeFrom(input);
-      return this;
-    }
-
-    public IBuilder<TMessage> MergeFrom(Stream input, ExtensionRegistry extensionRegistry) {
-      ((IBuilder) this).MergeFrom(input, extensionRegistry);
-      return this;
+      return ThisBuilder;
     }
 
-    /// <summary>
-    /// Overridden when optimized for speed.
-    /// </summary>
-    public virtual IBuilder<TMessage> MergeFrom(CodedInputStream input) {
-      ((IBuilder)this).MergeFrom(input);
-      return this;
-    }
-
-    /// <summary>
-    /// Overridden when optimized for speed.
-    /// </summary>
-    public virtual IBuilder<TMessage> MergeFrom(CodedInputStream input, ExtensionRegistry extensionRegistry) {
-      ((IBuilder)this).MergeFrom(input, extensionRegistry);
-      return this;
-    }
-    
     /// <summary>
     /// Like Build(), but will wrap UninitializedMessageException in
     /// InvalidProtocolBufferException.
@@ -219,10 +149,10 @@ namespace Google.ProtocolBuffers {
     }
 
     /// <summary>
-    /// Implementation of <see cref="IBuilder{T}.Build" />.
+    /// Implementation of <see cref="IBuilder{TMessage, TBuilder}.Build" />.
     /// TODO(jonskeet): This used to be generated for each class. Find out why.
     /// </summary>
-    public TMessage Build() {
+    public override TMessage Build() {
       if (!IsInitialized) {
         throw new UninitializedMessageException(MessageBeingBuilt);
       }
@@ -233,13 +163,5 @@ namespace Google.ProtocolBuffers {
       get { return MessageBeingBuilt.UnknownFields; }
       set { MessageBeingBuilt.SetUnknownFields(value); }
     }
-    
-    public abstract TMessage BuildPartial();
-    public abstract IBuilder<TMessage> Clone();
-    public abstract new IBuilder<TMessage> Clear();
-    public abstract TMessage DefaultInstanceForType { get; }
-    
-    public abstract class ExtendableBuilder : GeneratedBuilder<TMessage, TBuilder> {
-    }
   }
 }

csharp/ProtocolBuffers/GeneratedExtensionBase.cs

@@ -29,7 +29,7 @@ namespace Google.ProtocolBuffers {
   /// The interface implemented by both GeneratedException and GeneratedRepeatException,
   /// to make it easier to cope with repeats separately.
   /// </remarks>
-  public abstract class GeneratedExtensionBase<TContainer, TExtension> {
+  public abstract class GeneratedExtensionBase<TExtension> {
 
     private readonly FieldDescriptor descriptor;
     private readonly IMessage messageDefaultInstance;
@@ -73,8 +73,8 @@ namespace Google.ProtocolBuffers {
             // GeneratedExtension manually and gives it a different type.
             // This should not happen in normal use.  But, to be nice, we'll
             // copy the message to whatever type the caller was expecting.
-            return MessageDefaultInstance.CreateBuilderForType()
-                           .MergeFrom((IMessage)value).Build();
+            return MessageDefaultInstance.WeakCreateBuilderForType()
+                           .WeakMergeFrom((IMessage)value).WeakBuild();
           }
         case MappedType.Enum:
           // Just return a boxed int - that can be unboxed to the enum

csharp/ProtocolBuffers/GeneratedMessage.cs

@@ -13,9 +13,9 @@ namespace Google.ProtocolBuffers {
   /// most of the IMessage interface using reflection. Users
   /// can ignore this class as an implementation detail.
   /// </summary>
-  public abstract class GeneratedMessage<TMessage, TBuilder> : AbstractMessage, IMessage<TMessage>
+  public abstract class GeneratedMessage<TMessage, TBuilder> : AbstractMessage<TMessage, TBuilder>
       where TMessage : GeneratedMessage<TMessage, TBuilder> 
-      where TBuilder : IBuilder<TMessage> {
+      where TBuilder : GeneratedBuilder<TMessage, TBuilder> {
 
     private UnknownFieldSet unknownFields = UnknownFieldSet.DefaultInstance;
 
@@ -29,18 +29,6 @@ namespace Google.ProtocolBuffers {
       get { return InternalFieldAccessors.Descriptor; }
     }
 
-    protected override IMessage DefaultInstanceForTypeImpl {
-      get { return DefaultInstanceForType; }
-    }
-
-    protected override IBuilder CreateBuilderForTypeImpl() {
-      return CreateBuilderForType();
-    }
-
-    public abstract TMessage DefaultInstanceForType { get; }
-
-    public abstract IBuilder<TMessage> CreateBuilderForType();
-
     internal IDictionary<FieldDescriptor, Object> GetMutableFieldMap() {
 
       // Use a SortedList so we'll end up serializing fields in order

csharp/ProtocolBuffers/GeneratedRepeatException.cs

@@ -7,15 +7,15 @@ namespace Google.ProtocolBuffers {
   /// <summary>
   /// Class used to represent repeat extensions in generated classes.
   /// </summary>
-  public class GeneratedRepeatExtension<TContainer, TExtensionElement> : GeneratedExtensionBase<TContainer, IList<TExtensionElement>> {
+  public class GeneratedRepeatExtension<TExtensionElement> : GeneratedExtensionBase<IList<TExtensionElement>> {
     private GeneratedRepeatExtension(FieldDescriptor field) : base(field, typeof(TExtensionElement)) {
     }
 
-    public static GeneratedExtensionBase<TContainer, IList<TExtensionElement>> CreateInstance(FieldDescriptor descriptor) {
+    public static GeneratedExtensionBase<IList<TExtensionElement>> CreateInstance(FieldDescriptor descriptor) {
       if (!descriptor.IsRepeated) {
         throw new ArgumentException("Must call GeneratedRepeatExtension.CreateInstance() for repeated types.");
       }
-      return new GeneratedRepeatExtension<TContainer, TExtensionElement>(descriptor);
+      return new GeneratedRepeatExtension<TExtensionElement>(descriptor);
     }
 
     /// <summary>

csharp/ProtocolBuffers/GeneratedSingleExtension.cs

@@ -6,17 +6,15 @@ namespace Google.ProtocolBuffers {
   /// <summary>
   /// Generated extension for a singular field.
   /// </remarks>
-  public class GeneratedSingleExtension<TContainer, TExtension> : GeneratedExtensionBase<TContainer, TExtension>    
-      where TContainer : IMessage<TContainer> {
-
+  public class GeneratedSingleExtension<TExtension> : GeneratedExtensionBase<TExtension>  {
     internal GeneratedSingleExtension(FieldDescriptor descriptor) : base(descriptor, typeof(TExtension)) {
     }
 
-    public static GeneratedSingleExtension<TContainer, TExtension> CreateInstance(FieldDescriptor descriptor) {
+    public static GeneratedSingleExtension<TExtension> CreateInstance(FieldDescriptor descriptor) {
       if (descriptor.IsRepeated) {
         throw new ArgumentException("Must call GeneratedRepeateExtension.CreateInstance() for repeated types.");
       }
-      return new GeneratedSingleExtension<TContainer, TExtension>(descriptor);
+      return new GeneratedSingleExtension<TExtension>(descriptor);
     }
 
     public override object FromReflectionType(object value) {

csharp/ProtocolBuffers/IMessage.cs

@@ -21,11 +21,8 @@ using Google.ProtocolBuffers.Descriptors;
 namespace Google.ProtocolBuffers {
 
   /// <summary>
-  /// Non-generic interface implemented by all Protocol Buffers messages.
-  /// Some members are repeated in the generic interface but with a
-  /// type-specific signature. Type-safe implementations
-  /// are encouraged to implement these non-generic members explicitly,
-  /// and the generic members implicitly.
+  /// Non-generic interface used for all parts of the API which don't require
+  /// any type knowledge.
   /// </summary>
   public interface IMessage {
     /// <summary>
@@ -152,27 +149,17 @@ namespace Google.ProtocolBuffers {
     void WriteTo(Stream output);
     #endregion
 
-    #region Weakly typed members
     /// <summary>
-    /// Returns an instance of this message type with all fields set to
-    /// their default values. This may or may not be a singleton. This differs
-    /// from the DefaultInstance property of each generated message class in that this
-    /// method is an abstract method of IMessage whereas DefaultInstance is
-    /// a static property of a specific class. They return the same thing.
+    /// Creates a builder for the type, but in a weakly typed manner. This
+    /// is typically implemented by strongly typed builders by just returning
+    /// the result of CreateBuilderForType.
     /// </summary>
-    IMessage DefaultInstanceForType { get; }
+    IBuilder WeakCreateBuilderForType();
 
-    /// <summary>
-    /// Constructs a new builder for a message of the same type as this message.
-    /// </summary>
-    IBuilder CreateBuilderForType();
-    #endregion
+    IMessage WeakDefaultInstanceForType { get; }
   }
 
-  /// <summary>
-  /// Type-safe interface for all generated messages to implement.
-  /// </summary>
-  public interface IMessage<T> : IMessage where T : IMessage<T> {
+  public interface IMessage<TMessage> : IMessage {
     /// <summary>
     /// Returns an instance of this message type with all fields set to
     /// their default values. This may or may not be a singleton. This differs
@@ -180,13 +167,20 @@ namespace Google.ProtocolBuffers {
     /// method is an abstract method of IMessage whereas DefaultInstance is
     /// a static property of a specific class. They return the same thing.
     /// </summary>
-    new T DefaultInstanceForType { get; }
+    TMessage DefaultInstanceForType { get; }
+  }
 
+  /// <summary>
+  /// Type-safe interface for all generated messages to implement.
+  /// </summary>
+  public interface IMessage<TMessage, TBuilder> : IMessage<TMessage>
+      where TMessage : IMessage<TMessage, TBuilder> 
+      where TBuilder : IBuilder<TMessage, TBuilder> {
     #region Builders
     /// <summary>
     /// Constructs a new builder for a message of the same type as this message.
     /// </summary>
-    new IBuilder<T> CreateBuilderForType();
+    TBuilder CreateBuilderForType();
     #endregion
   }
 }

csharp/ProtocolBuffers/InvalidProtocolBufferException.cs

@@ -67,13 +67,13 @@ namespace Google.ProtocolBuffers {
     internal static InvalidProtocolBufferException RecursionLimitExceeded() {
       return new InvalidProtocolBufferException(
         "Protocol message had too many levels of nesting.  May be malicious.  " +
-        "Use CodedInputStream.setRecursionLimit() to increase the depth limit.");
+        "Use CodedInputStream.SetRecursionLimit() to increase the depth limit.");
     }
 
     internal static InvalidProtocolBufferException SizeLimitExceeded() {
       return new InvalidProtocolBufferException(
         "Protocol message was too large.  May be malicious.  " +
-        "Use CodedInputStream.setSizeLimit() to increase the size limit.");
+        "Use CodedInputStream.SetSizeLimit() to increase the size limit.");
     }
   }
 }

csharp/ProtocolBuffers/RpcUtil.cs

@@ -21,12 +21,13 @@ namespace Google.ProtocolBuffers {
     /// callback is given a message with a different descriptor, an
     /// exception will be thrown.
     /// </summary>
-    public static Action<IMessage> GeneralizeCallback<T>(Action<T> action, T defaultInstance)
-        where T : class, IMessage<T> {
+    public static Action<IMessage> GeneralizeCallback<TMessage, TBuilder>(Action<TMessage> action, TMessage defaultInstance)
+        where TMessage : class, IMessage<TMessage, TBuilder> 
+        where TBuilder : IBuilder<TMessage, TBuilder> {
       return message => {
-        T castMessage = message as T;
+        TMessage castMessage = message as TMessage;
         if (castMessage == null) {
-          castMessage = (T) defaultInstance.CreateBuilderForType().MergeFrom(message).Build();
+          castMessage = defaultInstance.CreateBuilderForType().MergeFrom(message).Build();
         }
         action(castMessage);
       };

csharp/ProtocolBuffers/TextFormat.cs

@@ -44,6 +44,7 @@ namespace Google.ProtocolBuffers {
     }
 
     private static void Print(IMessage message, TextGenerator generator) {
+      // TODO(jonskeet): Check why descriptor is never used.
       MessageDescriptor descriptor = message.DescriptorForType;
       foreach (KeyValuePair<FieldDescriptor, object> entry in message.AllFields) {
         PrintField(entry.Key, entry.Value, generator);

src/google/protobuf/compiler/csharp/csharp_extension.cc

@@ -57,12 +57,12 @@ void ExtensionGenerator::Generate(io::Printer* printer) {
   if (descriptor_->is_repeated()) {
     printer->Print(vars,
       "public static readonly\r\n"
-      "  pb::GeneratedExtensionBase<$containing_type$, scg::IList<$type$>> $name$ =\r\n"
-      "      pb::GeneratedRepeatExtension<$containing_type$, $type$>.CreateInstance(Descriptor.Extensions[$index$]);\r\n");
+      "  pb::GeneratedExtensionBase<scg::IList<$type$>> $name$ =\r\n"
+      "      pb::GeneratedRepeatExtension<$type$>.CreateInstance(Descriptor.Extensions[$index$]);\r\n");
   } else {
     printer->Print(vars,
-      "public static readonly pb::GeneratedExtensionBase<$containing_type$, $type$> $name$ =\r\n"
-      "      pb::GeneratedSingleExtension<$containing_type$, $type$>.CreateInstance(Descriptor.Extensions[$index$]);\r\n");
+      "public static readonly pb::GeneratedExtensionBase<$type$> $name$ =\r\n"
+      "      pb::GeneratedSingleExtension<$type$>.CreateInstance(Descriptor.Extensions[$index$]);\r\n");
   }
 }
 

src/google/protobuf/compiler/csharp/csharp_message.cc

@@ -423,7 +423,7 @@ void MessageGenerator::GenerateSerializeOneExtensionRange(
 void MessageGenerator::GenerateBuilder(io::Printer* printer) {
   printer->Print(
     "public static Builder CreateBuilder() { return new Builder(); }\r\n"
-    "public override IBuilder<$classname$> CreateBuilderForType() { return new Builder(); }\r\n"
+    "public override Builder CreateBuilderForType() { return new Builder(); }\r\n"
     "public static Builder CreateBuilder($classname$ prototype) {\r\n"
     "  return (Builder) new Builder().MergeFrom(prototype);\r\n"
     "}\r\n"
@@ -441,8 +441,14 @@ void MessageGenerator::GenerateBuilder(io::Printer* printer) {
       "classname", ClassName(descriptor_),
       "access", ClassAccessLevel(descriptor_->file()));
   }
+
   printer->Indent();
 
+  printer->Print(
+      "protected override Builder ThisBuilder {\r\n"
+      "  get { return this; }\r\n"
+      "}\r\n\r\n");
+
   GenerateCommonBuilderMethods(printer);
 
   if (descriptor_->file()->options().optimize_for() == FileOptions::SPEED) {
@@ -475,12 +481,12 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
     "  get { return result; }\r\n"
     "}\r\n"
     "\r\n"
-    "public override IBuilder<$classname$> Clear() {\r\n"
+    "public override Builder Clear() {\r\n"
     "  result = new $classname$();\r\n"
     "  return this;\r\n"
     "}\r\n"
     "\r\n"
-    "public override IBuilder<$classname$> Clone() {\r\n"
+    "public override Builder Clone() {\r\n"
     "  return new Builder().MergeFrom(result);\r\n"
     "}\r\n"
     "\r\n"
@@ -516,14 +522,14 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
 
   // -----------------------------------------------------------------
 
-  //TODO(jonskeet): Work out what this is really for...
   if (descriptor_->file()->options().optimize_for() == FileOptions::SPEED) {
     printer->Print(
-      "protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {\r\n"
+      /*
+      "protected override Builder MergeFrom(CodedInputStream data, ExtensionRegistry extensionRegistry) {\r\n"
       "  return MergeFrom(data, extensionRegistry);\r\n"
       "}\r\n"
-      "\r\n"
-      "public override IBuilder MergeFrom(pb::IMessage other) {\r\n"
+      "\r\n"*/
+      "public override Builder MergeFrom(pb::IMessage other) {\r\n"
       "  if (other is $classname$) {\r\n"
       "    return MergeFrom(($classname$) other);\r\n"
       "  } else {\r\n"
@@ -532,7 +538,7 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
       "  }\r\n"
       "}\r\n"
       "\r\n"
-      "public override IBuilder<$classname$> MergeFrom($classname$ other) {\r\n"
+      "public override Builder MergeFrom($classname$ other) {\r\n"
       // Optimization:  If other is the default instance, we know none of its
       //   fields are set so we can skip the merge.
       "  if (other == $classname$.DefaultInstance) return this;\r\n",
@@ -559,11 +565,11 @@ void MessageGenerator::GenerateBuilderParsingMethods(io::Printer* printer) {
     SortFieldsByNumber(descriptor_));
 
   printer->Print(
-    "public override IBuilder<$classname$> MergeFrom(pb::CodedInputStream input) {\r\n"
+    "public override Builder MergeFrom(pb::CodedInputStream input) {\r\n"
     "  return MergeFrom(input, pb::ExtensionRegistry.Empty);\r\n"
     "}\r\n"
     "\r\n"
-    "public override IBuilder<$classname$> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {\r\n",
+    "public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {\r\n",
     "classname", ClassName(descriptor_));
   printer->Indent();
 

src/google/protobuf/compiler/csharp/csharp_service.cc

@@ -199,7 +199,7 @@ void ServiceGenerator::GenerateStub(io::Printer* printer) {
       "    controller,\r\n"
       "    request,\r\n"
       "    $output$.DefaultInstance,\r\n"
-      "    pb::RpcUtil.GeneralizeCallback(done, $output$.DefaultInstance));\r\n"
+      "    pb::RpcUtil.GeneralizeCallback<$output$, $output$.Builder>(done, $output$.DefaultInstance));\r\n"
       "}\r\n");
   }