Implemented popsicle immutability for lists. Modified MessageStreamIterator to be singly generic.

csharp/ProtocolBuffers.Test/Collections/PopsicleListTest.cs

+using System;
+using System.Collections.Generic;
+using System.Text;
+using NUnit.Framework;
+
+namespace Google.ProtocolBuffers.Collections {
+  [TestFixture]
+  public class PopsicleListTest {
+
+    [Test]
+    public void MutatingOperationsOnFrozenList() {
+      PopsicleList<string> list = new PopsicleList<string>();
+      list.MakeReadOnly();
+      AssertNotSupported(() => list.Add(""));
+      AssertNotSupported(() => list.Clear());
+      AssertNotSupported(() => list.Insert(0, ""));
+      AssertNotSupported(() => list.Remove(""));
+      AssertNotSupported(() => list.RemoveAt(0));
+    }
+
+    [Test]
+    public void NonMutatingOperationsOnFrozenList() {
+      PopsicleList<string> list = new PopsicleList<string>();
+      list.MakeReadOnly();
+      Assert.IsFalse(list.Contains(""));
+      Assert.AreEqual(0, list.Count);
+      list.CopyTo(new string[5], 0);
+      list.GetEnumerator();
+      Assert.AreEqual(-1, list.IndexOf(""));
+      Assert.IsTrue(list.IsReadOnly);
+    }
+
+    [Test]
+    public void MutatingOperationsOnFluidList() {
+      PopsicleList<string> list = new PopsicleList<string>();
+      list.Add("");
+      list.Clear();
+      list.Insert(0, "");
+      list.Remove("");
+      list.Add("x"); // Just to make the next call valid
+      list.RemoveAt(0);
+    }
+
+    [Test]
+    public void NonMutatingOperationsOnFluidList() {
+      PopsicleList<string> list = new PopsicleList<string>();
+      Assert.IsFalse(list.Contains(""));
+      Assert.AreEqual(0, list.Count);
+      list.CopyTo(new string[5], 0);
+      list.GetEnumerator();
+      Assert.AreEqual(-1, list.IndexOf(""));
+      Assert.IsFalse(list.IsReadOnly);
+    }
+
+    private static void AssertNotSupported(Action action) {
+      try {
+        action();
+        Assert.Fail("Expected NotSupportedException");
+      } catch (NotSupportedException) {
+        // Expected
+      }
+    }
+  }
+}

csharp/ProtocolBuffers.Test/GeneratedMessageTest.cs

@@ -13,6 +13,8 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
+using System;
+using System.Collections.Generic;
 using Google.ProtocolBuffers.Descriptors;
 using Google.ProtocolBuffers.TestProtos;
 using NUnit.Framework;
@@ -28,7 +30,50 @@ namespace Google.ProtocolBuffers {
       reflectionTester = ReflectionTester.CreateTestAllTypesInstance();
       extensionsReflectionTester = ReflectionTester.CreateTestAllExtensionsInstance();
     }
-    
+
+    [Test]
+    public void RepeatedAddPrimitiveBeforeBuild() {
+      TestAllTypes message = new TestAllTypes.Builder { RepeatedInt32List = { 1, 2, 3 } }.Build();
+      TestUtil.AssertEqual(new int[]{1, 2, 3}, message.RepeatedInt32List);
+    }
+
+    [Test]
+    public void AddPrimitiveFailsAfterBuild() {
+      TestAllTypes.Builder builder = new TestAllTypes.Builder();
+      IList<int> list = builder.RepeatedInt32List;
+      list.Add(1); // Fine
+      builder.Build();
+
+      try {
+        list.Add(2);
+        Assert.Fail("List should be frozen");
+      } catch (NotSupportedException) {
+        // Expected
+      }
+    }
+
+    [Test]
+    public void RepeatedAddMessageBeforeBuild() {
+      TestAllTypes message = new TestAllTypes.Builder {
+          RepeatedNestedMessageList = { new TestAllTypes.Types.NestedMessage.Builder { Bb = 10 }.Build() } }.Build();
+      Assert.AreEqual(1, message.RepeatedNestedMessageCount);
+      Assert.AreEqual(10, message.RepeatedNestedMessageList[0].Bb);
+    }
+
+    [Test]
+    public void AddMessageFailsAfterBuild() {
+      TestAllTypes.Builder builder = new TestAllTypes.Builder();
+      IList<TestAllTypes.Types.NestedMessage> list = builder.RepeatedNestedMessageList;
+      builder.Build();
+
+      try {
+        list.Add(new TestAllTypes.Types.NestedMessage.Builder { Bb = 10 }.Build());
+        Assert.Fail("List should be frozen");
+      } catch (NotSupportedException) {
+        // Expected
+      }
+    }
+
     [Test]
     public void DefaultInstance() {
       Assert.AreSame(TestAllTypes.DefaultInstance, TestAllTypes.DefaultInstance.DefaultInstanceForType);

csharp/ProtocolBuffers.Test/MessageStreamIteratorTest.cs

@@ -11,7 +11,7 @@ namespace Google.ProtocolBuffers {
     [Test]
     public void ThreeMessagesInMemory() {
       MemoryStream stream = new MemoryStream(MessageStreamWriterTest.ThreeMessageData);      
-      IEnumerable<NestedMessage> iterator = MessageStreamIterator.FromStreamProvider<NestedMessage>(() => stream);
+      IEnumerable<NestedMessage> iterator = MessageStreamIterator<NestedMessage>.FromStreamProvider(() => stream);
       List<NestedMessage> messages = new List<NestedMessage>(iterator);
 
       Assert.AreEqual(3, messages.Count);

csharp/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj

@@ -50,6 +50,7 @@
     <Compile Include="ByteStringTest.cs" />
     <Compile Include="CodedInputStreamTest.cs" />
     <Compile Include="CodedOutputStreamTest.cs" />
+    <Compile Include="Collections\PopsicleListTest.cs" />
     <Compile Include="DescriptorsTest.cs" />
     <Compile Include="DynamicMessageTest.cs" />
     <Compile Include="GeneratedMessageTest.cs" />

csharp/ProtocolBuffers.Test/TestProtos/MessageWithNoOuter.cs

@@ -7,7 +7,7 @@ using scg = global::System.Collections.Generic;
 namespace Google.ProtocolBuffers.TestProtos {
   
   public sealed partial class MessageWithNoOuter : pb::GeneratedMessage<MessageWithNoOuter, MessageWithNoOuter.Builder> {
-    private static readonly MessageWithNoOuter defaultInstance = new MessageWithNoOuter();
+    private static readonly MessageWithNoOuter defaultInstance = new Builder().BuildPartial();
     public static MessageWithNoOuter DefaultInstance {
       get { return defaultInstance; }
     }
@@ -35,7 +35,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public sealed partial class NestedMessage : pb::GeneratedMessage<NestedMessage, NestedMessage.Builder> {
-        private static readonly NestedMessage defaultInstance = new NestedMessage();
+        private static readonly NestedMessage defaultInstance = new Builder().BuildPartial();
         public static NestedMessage DefaultInstance {
           get { return defaultInstance; }
         }
@@ -179,7 +179,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated .protobuf_unittest.TestAllTypes foreign = 2;
-    private scg::IList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes> foreign_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes> foreign_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes>();
     public scg::IList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes> ForeignList {
       get { return foreign_; } 
     }
@@ -278,9 +278,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override global::Google.ProtocolBuffers.TestProtos.MessageWithNoOuter BuildPartial() {
-        if (result.foreign_ != pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes>.Empty) {
-          result.foreign_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes>.AsReadOnly(result.foreign_);
-        }
+        result.foreign_.MakeReadOnly();
         global::Google.ProtocolBuffers.TestProtos.MessageWithNoOuter returnMe = result;
         result = null;
         return returnMe;
@@ -324,7 +322,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       
       // repeated .protobuf_unittest.TestAllTypes foreign = 2;
       public scg::IList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes> ForeignList {
-        get { return pbc::Lists.AsReadOnly(result.foreign_); }
+        get { return result.foreign_; }
       }
       public int ForeignCount {
         get { return result.ForeignCount; }
@@ -341,28 +339,19 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddForeign(global::Google.ProtocolBuffers.TestProtos.TestAllTypes value) {
-        if (result.foreign_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes>.Empty) {
-          result.foreign_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestAllTypes>();
-        }
         result.foreign_.Add(value);
         return this;
       }
       public Builder AddForeign(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Builder builderForValue) {
-        if (result.foreign_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes>.Empty) {
-          result.foreign_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestAllTypes>();
-        }
         result.foreign_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeForeign(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestAllTypes> values) {
-        if (result.foreign_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes>.Empty) {
-          result.foreign_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestAllTypes>();
-        }
         base.AddRange(values, result.foreign_);
         return this;
       }
       public Builder ClearForeign() {
-        result.foreign_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes>.Empty;
+        result.foreign_.Clear();
         return this;
       }
       

csharp/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs

@@ -55,7 +55,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   
   #region Messages
   public sealed partial class TestEmbedOptimizedForSize : pb::GeneratedMessage<TestEmbedOptimizedForSize, TestEmbedOptimizedForSize.Builder> {
-    private static readonly TestEmbedOptimizedForSize defaultInstance = new TestEmbedOptimizedForSize();
+    private static readonly TestEmbedOptimizedForSize defaultInstance = new Builder().BuildPartial();
     public static TestEmbedOptimizedForSize DefaultInstance {
       get { return defaultInstance; }
     }
@@ -87,7 +87,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated .protobuf_unittest.TestOptimizedForSize repeated_message = 2;
-    private scg::IList<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize> repeatedMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize> repeatedMessage_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize>();
     public scg::IList<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize> RepeatedMessageList {
       get { return repeatedMessage_; } 
     }
@@ -211,9 +211,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override global::Google.ProtocolBuffers.TestProtos.TestEmbedOptimizedForSize BuildPartial() {
-        if (result.repeatedMessage_ != pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize>.Empty) {
-          result.repeatedMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize>.AsReadOnly(result.repeatedMessage_);
-        }
+        result.repeatedMessage_.MakeReadOnly();
         global::Google.ProtocolBuffers.TestProtos.TestEmbedOptimizedForSize returnMe = result;
         result = null;
         return returnMe;
@@ -234,9 +232,6 @@ namespace Google.ProtocolBuffers.TestProtos {
           MergeOptionalMessage(other.OptionalMessage);
         }
         if (other.repeatedMessage_.Count != 0) {
-          if (result.repeatedMessage_.Count == 0) {
-            result.repeatedMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize>();
-          }
           base.AddRange(other.repeatedMessage_, result.repeatedMessage_);
         }
         this.MergeUnknownFields(other.UnknownFields);
@@ -321,7 +316,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       
       // repeated .protobuf_unittest.TestOptimizedForSize repeated_message = 2;
       public scg::IList<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize> RepeatedMessageList {
-        get { return pbc::Lists.AsReadOnly(result.repeatedMessage_); }
+        get { return result.repeatedMessage_; }
       }
       public int RepeatedMessageCount {
         get { return result.RepeatedMessageCount; }
@@ -338,28 +333,19 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedMessage(global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize value) {
-        if (result.repeatedMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize>.Empty) {
-          result.repeatedMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize>();
-        }
         result.repeatedMessage_.Add(value);
         return this;
       }
       public Builder AddRepeatedMessage(global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize.Builder builderForValue) {
-        if (result.repeatedMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize>.Empty) {
-          result.repeatedMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize>();
-        }
         result.repeatedMessage_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeRepeatedMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize> values) {
-        if (result.repeatedMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize>.Empty) {
-          result.repeatedMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize>();
-        }
         base.AddRange(values, result.repeatedMessage_);
         return this;
       }
       public Builder ClearRepeatedMessage() {
-        result.repeatedMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestOptimizedForSize>.Empty;
+        result.repeatedMessage_.Clear();
         return this;
       }
     }

csharp/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs

@@ -55,7 +55,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   
   #region Messages
   public sealed partial class ImportMessage : pb::GeneratedMessage<ImportMessage, ImportMessage.Builder> {
-    private static readonly ImportMessage defaultInstance = new ImportMessage();
+    private static readonly ImportMessage defaultInstance = new Builder().BuildPartial();
     public static ImportMessage DefaultInstance {
       get { return defaultInstance; }
     }

csharp/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs

@@ -95,7 +95,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   
   #region Messages
   public sealed partial class TestMessageSet : pb::ExtendableMessage<TestMessageSet, TestMessageSet.Builder> {
-    private static readonly TestMessageSet defaultInstance = new TestMessageSet();
+    private static readonly TestMessageSet defaultInstance = new Builder().BuildPartial();
     public static TestMessageSet DefaultInstance {
       get { return defaultInstance; }
     }
@@ -264,7 +264,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestMessageSetContainer : pb::GeneratedMessage<TestMessageSetContainer, TestMessageSetContainer.Builder> {
-    private static readonly TestMessageSetContainer defaultInstance = new TestMessageSetContainer();
+    private static readonly TestMessageSetContainer defaultInstance = new Builder().BuildPartial();
     public static TestMessageSetContainer DefaultInstance {
       get { return defaultInstance; }
     }
@@ -495,7 +495,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestMessageSetExtension1 : pb::GeneratedMessage<TestMessageSetExtension1, TestMessageSetExtension1.Builder> {
-    private static readonly TestMessageSetExtension1 defaultInstance = new TestMessageSetExtension1();
+    private static readonly TestMessageSetExtension1 defaultInstance = new Builder().BuildPartial();
     public static TestMessageSetExtension1 DefaultInstance {
       get { return defaultInstance; }
     }
@@ -709,7 +709,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestMessageSetExtension2 : pb::GeneratedMessage<TestMessageSetExtension2, TestMessageSetExtension2.Builder> {
-    private static readonly TestMessageSetExtension2 defaultInstance = new TestMessageSetExtension2();
+    private static readonly TestMessageSetExtension2 defaultInstance = new Builder().BuildPartial();
     public static TestMessageSetExtension2 DefaultInstance {
       get { return defaultInstance; }
     }
@@ -923,7 +923,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class RawMessageSet : pb::GeneratedMessage<RawMessageSet, RawMessageSet.Builder> {
-    private static readonly RawMessageSet defaultInstance = new RawMessageSet();
+    private static readonly RawMessageSet defaultInstance = new Builder().BuildPartial();
     public static RawMessageSet DefaultInstance {
       get { return defaultInstance; }
     }
@@ -947,7 +947,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     #region Nested types
     public static class Types {
       public sealed partial class Item : pb::GeneratedMessage<Item, Item.Builder> {
-        private static readonly Item defaultInstance = new Item();
+        private static readonly Item defaultInstance = new Builder().BuildPartial();
         public static Item DefaultInstance {
           get { return defaultInstance; }
         }
@@ -1201,7 +1201,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     #endregion
     
     // repeated group Item = 1 {
-    private scg::IList<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item> item_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item> item_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item>();
     public scg::IList<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item> ItemList {
       get { return item_; } 
     }
@@ -1316,9 +1316,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override global::Google.ProtocolBuffers.TestProtos.RawMessageSet BuildPartial() {
-        if (result.item_ != pbc::Lists<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item>.Empty) {
-          result.item_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item>.AsReadOnly(result.item_);
-        }
+        result.item_.MakeReadOnly();
         global::Google.ProtocolBuffers.TestProtos.RawMessageSet returnMe = result;
         result = null;
         return returnMe;
@@ -1336,9 +1334,6 @@ namespace Google.ProtocolBuffers.TestProtos {
       public override Builder MergeFrom(global::Google.ProtocolBuffers.TestProtos.RawMessageSet other) {
         if (other == global::Google.ProtocolBuffers.TestProtos.RawMessageSet.DefaultInstance) return this;
         if (other.item_.Count != 0) {
-          if (result.item_.Count == 0) {
-            result.item_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item>();
-          }
           base.AddRange(other.item_, result.item_);
         }
         this.MergeUnknownFields(other.UnknownFields);
@@ -1379,7 +1374,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       
       // repeated group Item = 1 {
       public scg::IList<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item> ItemList {
-        get { return pbc::Lists.AsReadOnly(result.item_); }
+        get { return result.item_; }
       }
       public int ItemCount {
         get { return result.ItemCount; }
@@ -1396,28 +1391,19 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddItem(global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item value) {
-        if (result.item_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item>.Empty) {
-          result.item_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item>();
-        }
         result.item_.Add(value);
         return this;
       }
       public Builder AddItem(global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item.Builder builderForValue) {
-        if (result.item_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item>.Empty) {
-          result.item_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item>();
-        }
         result.item_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeItem(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item> values) {
-        if (result.item_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item>.Empty) {
-          result.item_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item>();
-        }
         base.AddRange(values, result.item_);
         return this;
       }
       public Builder ClearItem() {
-        result.item_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.RawMessageSet.Types.Item>.Empty;
+        result.item_.Clear();
         return this;
       }
     }

csharp/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs

@@ -54,7 +54,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   
   #region Messages
   public sealed partial class TestOptimizedForSize : pb::ExtendableMessage<TestOptimizedForSize, TestOptimizedForSize.Builder> {
-    private static readonly TestOptimizedForSize defaultInstance = new TestOptimizedForSize();
+    private static readonly TestOptimizedForSize defaultInstance = new Builder().BuildPartial();
     public static TestOptimizedForSize DefaultInstance {
       get { return defaultInstance; }
     }

csharp/ProtocolBuffers/Collections/PopsicleList.cs

+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Collections;
+
+namespace Google.ProtocolBuffers.Collections {
+  /// <summary>
+  /// Proxies calls to a <see cref="List{T}" />, but allows the list
+  /// to be made read-only (with the <see cref="MakeReadOnly" /> method), 
+  /// after which any modifying methods throw <see cref="NotSupportedException" />.
+  /// </summary>
+  public sealed class PopsicleList<T> : IList<T> {
+
+    private readonly List<T> items = new List<T>();
+    private bool readOnly = false;
+
+    /// <summary>
+    /// Makes this list read-only ("freezes the popsicle"). From this
+    /// point on, mutating methods (Clear, Add etc) will throw a
+    /// NotSupportedException. There is no way of "defrosting" the list afterwards.
+    /// </summary>
+    public void MakeReadOnly() {
+      readOnly = true;
+    }
+
+    public int IndexOf(T item) {
+      return items.IndexOf(item);
+    }
+
+    public void Insert(int index, T item) {
+      ValidateModification();
+      items.Insert(index, item);
+    }
+
+    public void RemoveAt(int index) {
+      ValidateModification();
+      items.RemoveAt(index);
+    }
+
+    public T this[int index] {
+      get {
+        return items[index];
+      }
+      set {
+        ValidateModification();
+        items[index] = value;
+      }
+    }
+
+    public void Add(T item) {
+      ValidateModification();
+      items.Add(item);
+    }
+
+    public void Clear() {
+      ValidateModification();
+      items.Clear();
+    }
+
+    public bool Contains(T item) {
+      return items.Contains(item);
+    }
+
+    public void CopyTo(T[] array, int arrayIndex) {
+      items.CopyTo(array, arrayIndex);
+    }
+
+    public int Count {
+      get { return items.Count; }
+    }
+
+    public bool IsReadOnly {
+      get { return readOnly; }
+    }
+
+    public bool Remove(T item) {
+      ValidateModification();
+      return items.Remove(item);
+    }
+
+    public IEnumerator<T> GetEnumerator() {
+      return items.GetEnumerator();
+    }
+
+    IEnumerator IEnumerable.GetEnumerator() {
+      return GetEnumerator();
+    }
+
+    private void ValidateModification() {
+      if (readOnly) {
+        throw new NotSupportedException("List is read-only");
+      }
+    }
+  }
+}

csharp/ProtocolBuffers/Delegates.cs

-using System.IO;
-namespace Google.ProtocolBuffers {
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.
+// http://code.google.com/p/protobuf/
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+using System.IO;
 
+namespace Google.ProtocolBuffers {
   /// <summary>
   /// Delegate to return a stream when asked, used by MessageStreamIterator.
   /// </summary>
   public delegate Stream StreamProvider();
+
+  // These delegate declarations mirror the ones in .NET 3.5 for the sake of familiarity.
+  internal delegate TResult Func<TResult>();
+  internal delegate TResult Func<T, TResult>(T arg);
+  internal delegate TResult Func<T1, T2, TResult>(T1 arg1, T2 arg2);
+  internal delegate TResult Func<T1, T2, T3, TResult>(T1 arg1, T2 arg2, T3 arg3);
+  internal delegate TResult Func<T1, T2, T3, T4, TResult>(T1 arg1, T2 arg2, T3 arg3, T4 arg4);
+  internal delegate void Action();
+  internal delegate void Action<T1, T2>(T1 arg1, T2 arg2);
 }

csharp/ProtocolBuffers/FieldAccess/Delegates.cs

-// Protocol Buffers - Google's data interchange format
-// Copyright 2008 Google Inc.
-// http://code.google.com/p/protobuf/
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//      http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-namespace Google.ProtocolBuffers.FieldAccess {
-
-  // These delegate declarations mirror the ones in .NET 3.5 for the sake of familiarity.
-  internal delegate TResult Func<TResult>();
-  internal delegate TResult Func<T, TResult>(T arg);
-  internal delegate TResult Func<T1, T2, TResult>(T1 arg1, T2 arg2);
-  internal delegate TResult Func<T1, T2, T3, TResult>(T1 arg1, T2 arg2, T3 arg3);
-  internal delegate TResult Func<T1, T2, T3, T4, TResult>(T1 arg1, T2 arg2, T3 arg3, T4 arg4); 
-  internal delegate void Action<T1, T2>(T1 arg1, T2 arg2);
-}

csharp/ProtocolBuffers/ProtocolBuffers.csproj

@@ -41,6 +41,7 @@
     <Compile Include="AbstractBuilder.cs" />
     <Compile Include="AbstractMessage.cs" />
     <Compile Include="ByteString.cs" />
+    <Compile Include="Collections\PopsicleList.cs" />
     <Compile Include="Delegates.cs" />
     <Compile Include="CodedInputStream.cs" />
     <Compile Include="CodedOutputStream.cs" />
@@ -72,7 +73,6 @@
     <Compile Include="ExtendableMessage.cs" />
     <Compile Include="ExtensionInfo.cs" />
     <Compile Include="ExtensionRegistry.cs" />
-    <Compile Include="FieldAccess\Delegates.cs" />
     <Compile Include="FieldAccess\ReflectionUtil.cs" />
     <Compile Include="FieldAccess\SingleEnumAccessor.cs" />
     <Compile Include="FieldAccess\SingleMessageAccessor.cs" />

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

@@ -212,7 +212,8 @@ void MessageGenerator::Generate(io::Printer* printer) {
   }
   printer->Indent();
   printer->Print(
-    "private static readonly $classname$ defaultInstance = new $classname$();\r\n"
+    // Must call Build() to make sure all lists are made read-only
+    "private static readonly $classname$ defaultInstance = new Builder().BuildPartial();\r\n"
     "public static $classname$ DefaultInstance {\r\n"
     "  get { return defaultInstance; }\r\n"
     "}\r\n"

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

@@ -175,9 +175,9 @@ RepeatedMessageFieldGenerator::~RepeatedMessageFieldGenerator() {}
 void RepeatedMessageFieldGenerator::
 GenerateMembers(io::Printer* printer) const {
   printer->Print(variables_,
-    "private scg::IList<$type$> $name$_ = pbc::Lists<$type$>.Empty;\r\n"
+    "private pbc::PopsicleList<$type$> $name$_ = new pbc::PopsicleList<$type$>();\r\n"
     "public scg::IList<$type$> $capitalized_name$List {\r\n"
-    "  get { return $name$_; } \r\n"   // note:  unmodifiable list
+    "  get { return $name$_; } \r\n"   // Will be unmodifiable by the time it's exposed
     "}\r\n"
     "public int $capitalized_name$Count\r\n"
     "  { get { return $name$_.Count; }\r\n"
@@ -190,12 +190,10 @@ GenerateMembers(io::Printer* printer) const {
 void RepeatedMessageFieldGenerator::
 GenerateBuilderMembers(io::Printer* printer) const {
   printer->Print(variables_,
-    // Note:  We return an unmodifiable list because otherwise the caller
-    //   could hold on to the returned list and modify it after the message
-    //   has been built, thus mutating the message which is supposed to be
-    //   immutable.
+    // Note:  We can return the original list here, because we
+    // make it read-only when we build.
     "public scg::IList<$type$> $capitalized_name$List {\r\n"
-    "  get { return pbc::Lists.AsReadOnly(result.$name$_); }\r\n"
+    "  get { return result.$name$_; }\r\n"
     "}\r\n"
     "public int $capitalized_name$Count {\r\n"
     "  get { return result.$capitalized_name$Count; }\r\n"
@@ -212,28 +210,19 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "  return this;\r\n"
     "}\r\n"
     "public Builder Add$capitalized_name$($type$ value) {\r\n"
-    "  if (result.$name$_ == pbc::Lists<$type$>.Empty) {\r\n"
-    "    result.$name$_ = new scg::List<$type$>();\r\n"
-    "  }\r\n"
     "  result.$name$_.Add(value);\r\n"
     "  return this;\r\n"
     "}\r\n"
     "public Builder Add$capitalized_name$($type$.Builder builderForValue) {\r\n"
-    "  if (result.$name$_ == pbc::Lists<$type$>.Empty) {\r\n"
-    "    result.$name$_ = new scg::List<$type$>();\r\n"
-    "  }\r\n"
     "  result.$name$_.Add(builderForValue.Build());\r\n"
     "  return this;\r\n"
     "}\r\n"
     "public Builder AddRange$capitalized_name$(scg::IEnumerable<$type$> values) {\r\n"
-    "  if (result.$name$_ == pbc::Lists<$type$>.Empty) {\r\n"
-    "    result.$name$_ = new scg::List<$type$>();\r\n"
-    "  }\r\n"
     "  base.AddRange(values, result.$name$_);\r\n"
     "  return this;\r\n"
     "}\r\n"
     "public Builder Clear$capitalized_name$() {\r\n"
-    "  result.$name$_ = pbc::Lists<$type$>.Empty;\r\n"
+    "  result.$name$_.Clear();\r\n"
     "  return this;\r\n"
     "}\r\n");
 }
@@ -242,9 +231,6 @@ void RepeatedMessageFieldGenerator::
 GenerateMergingCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if (other.$name$_.Count != 0) {\r\n"
-    "  if (result.$name$_.Count == 0) {\r\n"
-    "    result.$name$_ = new scg::List<$type$>();\r\n"
-    "  }\r\n"
     "  base.AddRange(other.$name$_, result.$name$_);\r\n"
     "}\r\n");
 }
@@ -252,9 +238,7 @@ GenerateMergingCode(io::Printer* printer) const {
 void RepeatedMessageFieldGenerator::
 GenerateBuildingCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "if (result.$name$_ != pbc::Lists<$type$>.Empty) {\r\n"
-    "  result.$name$_ = pbc::Lists<$type$>.AsReadOnly(result.$name$_);\r\n"
-    "}\r\n");
+    "result.$name$_.MakeReadOnly();\r\n");
 }
 
 void RepeatedMessageFieldGenerator::

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

@@ -239,9 +239,9 @@ RepeatedPrimitiveFieldGenerator::~RepeatedPrimitiveFieldGenerator() {}
 void RepeatedPrimitiveFieldGenerator::
 GenerateMembers(io::Printer* printer) const {
   printer->Print(variables_,
-    "private scg::IList<$type$> $name$_ = pbc::Lists<$type$>.Empty;\r\n"
+    "private pbc::PopsicleList<$type$> $name$_ = new pbc::PopsicleList<$type$>();\r\n"
     "public scg::IList<$type$> $capitalized_name$List {\r\n"
-    "  get { return $name$_; }\r\n"   // note:  unmodifiable list
+    "  get { return $name$_; } \r\n"   // Will be unmodifiable by the time it's exposed
     "}\r\n"
     "public int $capitalized_name$Count {\r\n"
     "  get { return $name$_.Count; }\r\n"
@@ -254,12 +254,10 @@ GenerateMembers(io::Printer* printer) const {
 void RepeatedPrimitiveFieldGenerator::
 GenerateBuilderMembers(io::Printer* printer) const {
   printer->Print(variables_,
-    // Note:  We return an unmodifiable list because otherwise the caller
-    //   could hold on to the returned list and modify it after the message
-    //   has been built, thus mutating the message which is supposed to be
-    //   immutable. This unfortunately limits the use for collection initializers...
+    // Note:  We can return the original list here, because we
+    // make it read-only when we build.
     "public scg::IList<$type$> $capitalized_name$List {\r\n"
-    "  get { return pbc::Lists<$type$>.AsReadOnly(result.$name$_); }\r\n"
+    "  get { return result.$name$_; }\r\n"
     "}\r\n"
     "public int $capitalized_name$Count {\r\n"
     "  get { return result.$capitalized_name$Count; }\r\n"
@@ -272,21 +270,15 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "  return this;\r\n"
     "}\r\n"
     "public Builder Add$capitalized_name$($type$ value) {\r\n"
-    "  if (result.$name$_.Count == 0) {\r\n"
-    "    result.$name$_ = new scg::List<$type$>();\r\n"
-    "  }\r\n"
     "  result.$name$_.Add(value);\r\n"
     "  return this;\r\n"
     "}\r\n"
     "public Builder AddRange$capitalized_name$(scg::IEnumerable<$type$> values) {\r\n"
-    "  if (result.$name$_.Count == 0) {\r\n"
-    "    result.$name$_ = new scg::List<$type$>();\r\n"
-    "  }\r\n"
     "  base.AddRange(values, result.$name$_);\r\n"
     "  return this;\r\n"
     "}\r\n"
     "public Builder Clear$capitalized_name$() {\r\n"
-    "  result.$name$_ = pbc::Lists<$type$>.Empty;\r\n"
+    "  result.$name$_.Clear();\r\n"
     "  return this;\r\n"
     "}\r\n");
 }
@@ -295,9 +287,6 @@ void RepeatedPrimitiveFieldGenerator::
 GenerateMergingCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if (other.$name$_.Count != 0) {\r\n"
-    "  if (result.$name$_.Count == 0) {\r\n"
-    "    result.$name$_ = new scg::List<$type$>();\r\n"
-    "  }\r\n"
     "  base.AddRange(other.$name$_, result.$name$_);\r\n"
     "}\r\n");
 }
@@ -305,7 +294,7 @@ GenerateMergingCode(io::Printer* printer) const {
 void RepeatedPrimitiveFieldGenerator::
 GenerateBuildingCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "result.$name$_ = pbc::Lists<$type$>.AsReadOnly(result.$name$_);\r\n");
+    "result.$name$_.MakeReadOnly();\r\n");
 }
 
 void RepeatedPrimitiveFieldGenerator::