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

16 files changed, 580 insertions, 863 deletions

diff --git a/csharp/ProtocolBuffers.Test/Collections/PopsicleListTest.cs b/csharp/ProtocolBuffers.Test/Collections/PopsicleListTest.cs
new file mode 100644
index 00000000..6943672d
--- /dev/null
+++ b/csharp/ProtocolBuffers.Test/Collections/PopsicleListTest.cs
@@ -0,0 +1,64 @@
+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
+      }
+    }
+  }
+}
diff --git a/csharp/ProtocolBuffers.Test/GeneratedMessageTest.cs b/csharp/ProtocolBuffers.Test/GeneratedMessageTest.cs
index 9a08ed95..f51f9755 100644
--- a/csharp/ProtocolBuffers.Test/GeneratedMessageTest.cs
+++ b/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);
diff --git a/csharp/ProtocolBuffers.Test/MessageStreamIteratorTest.cs b/csharp/ProtocolBuffers.Test/MessageStreamIteratorTest.cs
index 063f06d5..0cccd4a7 100644
--- a/csharp/ProtocolBuffers.Test/MessageStreamIteratorTest.cs
+++ b/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);
diff --git a/csharp/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj b/csharp/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj
index 027a159f..99de695e 100644
--- a/csharp/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj
+++ b/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" />
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/MessageWithNoOuter.cs b/csharp/ProtocolBuffers.Test/TestProtos/MessageWithNoOuter.cs
index 6e44a0c9..64f09f86 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/MessageWithNoOuter.cs
+++ b/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;
       }
       
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
index cae05bf8..8f4f3076 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
+++ b/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;
       }
     }
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
index 5713e1c9..7d8d1d0e 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
+++ b/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; }
     }
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs
index b3b53adf..e03eac92 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs
+++ b/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;
       }
     }
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs
index 52143f2c..de07d033 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs
+++ b/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; }
     }
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs
index 167f8718..a971832b 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs
+++ b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs
@@ -975,7 +975,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   
   #region Messages
   public sealed partial class TestAllTypes : pb::GeneratedMessage<TestAllTypes, TestAllTypes.Builder> {
-    private static readonly TestAllTypes defaultInstance = new TestAllTypes();
+    private static readonly TestAllTypes defaultInstance = new Builder().BuildPartial();
     public static TestAllTypes DefaultInstance {
       get { return defaultInstance; }
     }
@@ -1005,7 +1005,7 @@ 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; }
         }
@@ -1212,7 +1212,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public sealed partial class OptionalGroup : pb::GeneratedMessage<OptionalGroup, OptionalGroup.Builder> {
-        private static readonly OptionalGroup defaultInstance = new OptionalGroup();
+        private static readonly OptionalGroup defaultInstance = new Builder().BuildPartial();
         public static OptionalGroup DefaultInstance {
           get { return defaultInstance; }
         }
@@ -1419,7 +1419,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public sealed partial class RepeatedGroup : pb::GeneratedMessage<RepeatedGroup, RepeatedGroup.Builder> {
-        private static readonly RepeatedGroup defaultInstance = new RepeatedGroup();
+        private static readonly RepeatedGroup defaultInstance = new Builder().BuildPartial();
         public static RepeatedGroup DefaultInstance {
           get { return defaultInstance; }
         }
@@ -1863,9 +1863,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated int32 repeated_int32 = 31;
-    private scg::IList<int> repeatedInt32_ = pbc::Lists<int>.Empty;
+    private pbc::PopsicleList<int> repeatedInt32_ = new pbc::PopsicleList<int>();
     public scg::IList<int> RepeatedInt32List {
-      get { return repeatedInt32_; }
+      get { return repeatedInt32_; } 
     }
     public int RepeatedInt32Count {
       get { return repeatedInt32_.Count; }
@@ -1875,9 +1875,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated int64 repeated_int64 = 32;
-    private scg::IList<long> repeatedInt64_ = pbc::Lists<long>.Empty;
+    private pbc::PopsicleList<long> repeatedInt64_ = new pbc::PopsicleList<long>();
     public scg::IList<long> RepeatedInt64List {
-      get { return repeatedInt64_; }
+      get { return repeatedInt64_; } 
     }
     public int RepeatedInt64Count {
       get { return repeatedInt64_.Count; }
@@ -1887,9 +1887,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated uint32 repeated_uint32 = 33;
-    private scg::IList<uint> repeatedUint32_ = pbc::Lists<uint>.Empty;
+    private pbc::PopsicleList<uint> repeatedUint32_ = new pbc::PopsicleList<uint>();
     public scg::IList<uint> RepeatedUint32List {
-      get { return repeatedUint32_; }
+      get { return repeatedUint32_; } 
     }
     public int RepeatedUint32Count {
       get { return repeatedUint32_.Count; }
@@ -1899,9 +1899,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated uint64 repeated_uint64 = 34;
-    private scg::IList<ulong> repeatedUint64_ = pbc::Lists<ulong>.Empty;
+    private pbc::PopsicleList<ulong> repeatedUint64_ = new pbc::PopsicleList<ulong>();
     public scg::IList<ulong> RepeatedUint64List {
-      get { return repeatedUint64_; }
+      get { return repeatedUint64_; } 
     }
     public int RepeatedUint64Count {
       get { return repeatedUint64_.Count; }
@@ -1911,9 +1911,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated sint32 repeated_sint32 = 35;
-    private scg::IList<int> repeatedSint32_ = pbc::Lists<int>.Empty;
+    private pbc::PopsicleList<int> repeatedSint32_ = new pbc::PopsicleList<int>();
     public scg::IList<int> RepeatedSint32List {
-      get { return repeatedSint32_; }
+      get { return repeatedSint32_; } 
     }
     public int RepeatedSint32Count {
       get { return repeatedSint32_.Count; }
@@ -1923,9 +1923,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated sint64 repeated_sint64 = 36;
-    private scg::IList<long> repeatedSint64_ = pbc::Lists<long>.Empty;
+    private pbc::PopsicleList<long> repeatedSint64_ = new pbc::PopsicleList<long>();
     public scg::IList<long> RepeatedSint64List {
-      get { return repeatedSint64_; }
+      get { return repeatedSint64_; } 
     }
     public int RepeatedSint64Count {
       get { return repeatedSint64_.Count; }
@@ -1935,9 +1935,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated fixed32 repeated_fixed32 = 37;
-    private scg::IList<uint> repeatedFixed32_ = pbc::Lists<uint>.Empty;
+    private pbc::PopsicleList<uint> repeatedFixed32_ = new pbc::PopsicleList<uint>();
     public scg::IList<uint> RepeatedFixed32List {
-      get { return repeatedFixed32_; }
+      get { return repeatedFixed32_; } 
     }
     public int RepeatedFixed32Count {
       get { return repeatedFixed32_.Count; }
@@ -1947,9 +1947,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated fixed64 repeated_fixed64 = 38;
-    private scg::IList<ulong> repeatedFixed64_ = pbc::Lists<ulong>.Empty;
+    private pbc::PopsicleList<ulong> repeatedFixed64_ = new pbc::PopsicleList<ulong>();
     public scg::IList<ulong> RepeatedFixed64List {
-      get { return repeatedFixed64_; }
+      get { return repeatedFixed64_; } 
     }
     public int RepeatedFixed64Count {
       get { return repeatedFixed64_.Count; }
@@ -1959,9 +1959,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated sfixed32 repeated_sfixed32 = 39;
-    private scg::IList<int> repeatedSfixed32_ = pbc::Lists<int>.Empty;
+    private pbc::PopsicleList<int> repeatedSfixed32_ = new pbc::PopsicleList<int>();
     public scg::IList<int> RepeatedSfixed32List {
-      get { return repeatedSfixed32_; }
+      get { return repeatedSfixed32_; } 
     }
     public int RepeatedSfixed32Count {
       get { return repeatedSfixed32_.Count; }
@@ -1971,9 +1971,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated sfixed64 repeated_sfixed64 = 40;
-    private scg::IList<long> repeatedSfixed64_ = pbc::Lists<long>.Empty;
+    private pbc::PopsicleList<long> repeatedSfixed64_ = new pbc::PopsicleList<long>();
     public scg::IList<long> RepeatedSfixed64List {
-      get { return repeatedSfixed64_; }
+      get { return repeatedSfixed64_; } 
     }
     public int RepeatedSfixed64Count {
       get { return repeatedSfixed64_.Count; }
@@ -1983,9 +1983,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated float repeated_float = 41;
-    private scg::IList<float> repeatedFloat_ = pbc::Lists<float>.Empty;
+    private pbc::PopsicleList<float> repeatedFloat_ = new pbc::PopsicleList<float>();
     public scg::IList<float> RepeatedFloatList {
-      get { return repeatedFloat_; }
+      get { return repeatedFloat_; } 
     }
     public int RepeatedFloatCount {
       get { return repeatedFloat_.Count; }
@@ -1995,9 +1995,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated double repeated_double = 42;
-    private scg::IList<double> repeatedDouble_ = pbc::Lists<double>.Empty;
+    private pbc::PopsicleList<double> repeatedDouble_ = new pbc::PopsicleList<double>();
     public scg::IList<double> RepeatedDoubleList {
-      get { return repeatedDouble_; }
+      get { return repeatedDouble_; } 
     }
     public int RepeatedDoubleCount {
       get { return repeatedDouble_.Count; }
@@ -2007,9 +2007,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated bool repeated_bool = 43;
-    private scg::IList<bool> repeatedBool_ = pbc::Lists<bool>.Empty;
+    private pbc::PopsicleList<bool> repeatedBool_ = new pbc::PopsicleList<bool>();
     public scg::IList<bool> RepeatedBoolList {
-      get { return repeatedBool_; }
+      get { return repeatedBool_; } 
     }
     public int RepeatedBoolCount {
       get { return repeatedBool_.Count; }
@@ -2019,9 +2019,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated string repeated_string = 44;
-    private scg::IList<string> repeatedString_ = pbc::Lists<string>.Empty;
+    private pbc::PopsicleList<string> repeatedString_ = new pbc::PopsicleList<string>();
     public scg::IList<string> RepeatedStringList {
-      get { return repeatedString_; }
+      get { return repeatedString_; } 
     }
     public int RepeatedStringCount {
       get { return repeatedString_.Count; }
@@ -2031,9 +2031,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated bytes repeated_bytes = 45;
-    private scg::IList<pb::ByteString> repeatedBytes_ = pbc::Lists<pb::ByteString>.Empty;
+    private pbc::PopsicleList<pb::ByteString> repeatedBytes_ = new pbc::PopsicleList<pb::ByteString>();
     public scg::IList<pb::ByteString> RepeatedBytesList {
-      get { return repeatedBytes_; }
+      get { return repeatedBytes_; } 
     }
     public int RepeatedBytesCount {
       get { return repeatedBytes_.Count; }
@@ -2043,7 +2043,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated group RepeatedGroup = 46 {
-    private scg::IList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup> repeatedGroup_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup> repeatedGroup_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup>();
     public scg::IList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup> RepeatedGroupList {
       get { return repeatedGroup_; } 
     }
@@ -2055,7 +2055,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated .protobuf_unittest.TestAllTypes.NestedMessage repeated_nested_message = 48;
-    private scg::IList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage> repeatedNestedMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage> repeatedNestedMessage_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage>();
     public scg::IList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage> RepeatedNestedMessageList {
       get { return repeatedNestedMessage_; } 
     }
@@ -2067,7 +2067,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated .protobuf_unittest.ForeignMessage repeated_foreign_message = 49;
-    private scg::IList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> repeatedForeignMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> repeatedForeignMessage_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
     public scg::IList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> RepeatedForeignMessageList {
       get { return repeatedForeignMessage_; } 
     }
@@ -2079,7 +2079,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated .protobuf_unittest_import.ImportMessage repeated_import_message = 50;
-    private scg::IList<global::Google.ProtocolBuffers.TestProtos.ImportMessage> repeatedImportMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ImportMessage>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.ImportMessage> repeatedImportMessage_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.ImportMessage>();
     public scg::IList<global::Google.ProtocolBuffers.TestProtos.ImportMessage> RepeatedImportMessageList {
       get { return repeatedImportMessage_; } 
     }
@@ -2127,9 +2127,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated string repeated_string_piece = 54 [ctype = STRING_PIECE];
-    private scg::IList<string> repeatedStringPiece_ = pbc::Lists<string>.Empty;
+    private pbc::PopsicleList<string> repeatedStringPiece_ = new pbc::PopsicleList<string>();
     public scg::IList<string> RepeatedStringPieceList {
-      get { return repeatedStringPiece_; }
+      get { return repeatedStringPiece_; } 
     }
     public int RepeatedStringPieceCount {
       get { return repeatedStringPiece_.Count; }
@@ -2139,9 +2139,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated string repeated_cord = 55 [ctype = CORD];
-    private scg::IList<string> repeatedCord_ = pbc::Lists<string>.Empty;
+    private pbc::PopsicleList<string> repeatedCord_ = new pbc::PopsicleList<string>();
     public scg::IList<string> RepeatedCordList {
-      get { return repeatedCord_; }
+      get { return repeatedCord_; } 
     }
     public int RepeatedCordCount {
       get { return repeatedCord_.Count; }
@@ -2873,38 +2873,30 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override global::Google.ProtocolBuffers.TestProtos.TestAllTypes BuildPartial() {
-        result.repeatedInt32_ = pbc::Lists<int>.AsReadOnly(result.repeatedInt32_);
-        result.repeatedInt64_ = pbc::Lists<long>.AsReadOnly(result.repeatedInt64_);
-        result.repeatedUint32_ = pbc::Lists<uint>.AsReadOnly(result.repeatedUint32_);
-        result.repeatedUint64_ = pbc::Lists<ulong>.AsReadOnly(result.repeatedUint64_);
-        result.repeatedSint32_ = pbc::Lists<int>.AsReadOnly(result.repeatedSint32_);
-        result.repeatedSint64_ = pbc::Lists<long>.AsReadOnly(result.repeatedSint64_);
-        result.repeatedFixed32_ = pbc::Lists<uint>.AsReadOnly(result.repeatedFixed32_);
-        result.repeatedFixed64_ = pbc::Lists<ulong>.AsReadOnly(result.repeatedFixed64_);
-        result.repeatedSfixed32_ = pbc::Lists<int>.AsReadOnly(result.repeatedSfixed32_);
-        result.repeatedSfixed64_ = pbc::Lists<long>.AsReadOnly(result.repeatedSfixed64_);
-        result.repeatedFloat_ = pbc::Lists<float>.AsReadOnly(result.repeatedFloat_);
-        result.repeatedDouble_ = pbc::Lists<double>.AsReadOnly(result.repeatedDouble_);
-        result.repeatedBool_ = pbc::Lists<bool>.AsReadOnly(result.repeatedBool_);
-        result.repeatedString_ = pbc::Lists<string>.AsReadOnly(result.repeatedString_);
-        result.repeatedBytes_ = pbc::Lists<pb::ByteString>.AsReadOnly(result.repeatedBytes_);
-        if (result.repeatedGroup_ != pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup>.Empty) {
-          result.repeatedGroup_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup>.AsReadOnly(result.repeatedGroup_);
-        }
-        if (result.repeatedNestedMessage_ != pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage>.Empty) {
-          result.repeatedNestedMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage>.AsReadOnly(result.repeatedNestedMessage_);
-        }
-        if (result.repeatedForeignMessage_ != pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty) {
-          result.repeatedForeignMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.AsReadOnly(result.repeatedForeignMessage_);
-        }
-        if (result.repeatedImportMessage_ != pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ImportMessage>.Empty) {
-          result.repeatedImportMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ImportMessage>.AsReadOnly(result.repeatedImportMessage_);
-        }
+        result.repeatedInt32_.MakeReadOnly();
+        result.repeatedInt64_.MakeReadOnly();
+        result.repeatedUint32_.MakeReadOnly();
+        result.repeatedUint64_.MakeReadOnly();
+        result.repeatedSint32_.MakeReadOnly();
+        result.repeatedSint64_.MakeReadOnly();
+        result.repeatedFixed32_.MakeReadOnly();
+        result.repeatedFixed64_.MakeReadOnly();
+        result.repeatedSfixed32_.MakeReadOnly();
+        result.repeatedSfixed64_.MakeReadOnly();
+        result.repeatedFloat_.MakeReadOnly();
+        result.repeatedDouble_.MakeReadOnly();
+        result.repeatedBool_.MakeReadOnly();
+        result.repeatedString_.MakeReadOnly();
+        result.repeatedBytes_.MakeReadOnly();
+        result.repeatedGroup_.MakeReadOnly();
+        result.repeatedNestedMessage_.MakeReadOnly();
+        result.repeatedForeignMessage_.MakeReadOnly();
+        result.repeatedImportMessage_.MakeReadOnly();
         result.repeatedNestedEnum_ = pbc::Lists.AsReadOnly(result.repeatedNestedEnum_);
         result.repeatedForeignEnum_ = pbc::Lists.AsReadOnly(result.repeatedForeignEnum_);
         result.repeatedImportEnum_ = pbc::Lists.AsReadOnly(result.repeatedImportEnum_);
-        result.repeatedStringPiece_ = pbc::Lists<string>.AsReadOnly(result.repeatedStringPiece_);
-        result.repeatedCord_ = pbc::Lists<string>.AsReadOnly(result.repeatedCord_);
+        result.repeatedStringPiece_.MakeReadOnly();
+        result.repeatedCord_.MakeReadOnly();
         global::Google.ProtocolBuffers.TestProtos.TestAllTypes returnMe = result;
         result = null;
         return returnMe;
@@ -2994,117 +2986,60 @@ namespace Google.ProtocolBuffers.TestProtos {
           OptionalCord = other.OptionalCord;
         }
         if (other.repeatedInt32_.Count != 0) {
-          if (result.repeatedInt32_.Count == 0) {
-            result.repeatedInt32_ = new scg::List<int>();
-          }
           base.AddRange(other.repeatedInt32_, result.repeatedInt32_);
         }
         if (other.repeatedInt64_.Count != 0) {
-          if (result.repeatedInt64_.Count == 0) {
-            result.repeatedInt64_ = new scg::List<long>();
-          }
           base.AddRange(other.repeatedInt64_, result.repeatedInt64_);
         }
         if (other.repeatedUint32_.Count != 0) {
-          if (result.repeatedUint32_.Count == 0) {
-            result.repeatedUint32_ = new scg::List<uint>();
-          }
           base.AddRange(other.repeatedUint32_, result.repeatedUint32_);
         }
         if (other.repeatedUint64_.Count != 0) {
-          if (result.repeatedUint64_.Count == 0) {
-            result.repeatedUint64_ = new scg::List<ulong>();
-          }
           base.AddRange(other.repeatedUint64_, result.repeatedUint64_);
         }
         if (other.repeatedSint32_.Count != 0) {
-          if (result.repeatedSint32_.Count == 0) {
-            result.repeatedSint32_ = new scg::List<int>();
-          }
           base.AddRange(other.repeatedSint32_, result.repeatedSint32_);
         }
         if (other.repeatedSint64_.Count != 0) {
-          if (result.repeatedSint64_.Count == 0) {
-            result.repeatedSint64_ = new scg::List<long>();
-          }
           base.AddRange(other.repeatedSint64_, result.repeatedSint64_);
         }
         if (other.repeatedFixed32_.Count != 0) {
-          if (result.repeatedFixed32_.Count == 0) {
-            result.repeatedFixed32_ = new scg::List<uint>();
-          }
           base.AddRange(other.repeatedFixed32_, result.repeatedFixed32_);
         }
         if (other.repeatedFixed64_.Count != 0) {
-          if (result.repeatedFixed64_.Count == 0) {
-            result.repeatedFixed64_ = new scg::List<ulong>();
-          }
           base.AddRange(other.repeatedFixed64_, result.repeatedFixed64_);
         }
         if (other.repeatedSfixed32_.Count != 0) {
-          if (result.repeatedSfixed32_.Count == 0) {
-            result.repeatedSfixed32_ = new scg::List<int>();
-          }
           base.AddRange(other.repeatedSfixed32_, result.repeatedSfixed32_);
         }
         if (other.repeatedSfixed64_.Count != 0) {
-          if (result.repeatedSfixed64_.Count == 0) {
-            result.repeatedSfixed64_ = new scg::List<long>();
-          }
           base.AddRange(other.repeatedSfixed64_, result.repeatedSfixed64_);
         }
         if (other.repeatedFloat_.Count != 0) {
-          if (result.repeatedFloat_.Count == 0) {
-            result.repeatedFloat_ = new scg::List<float>();
-          }
           base.AddRange(other.repeatedFloat_, result.repeatedFloat_);
         }
         if (other.repeatedDouble_.Count != 0) {
-          if (result.repeatedDouble_.Count == 0) {
-            result.repeatedDouble_ = new scg::List<double>();
-          }
           base.AddRange(other.repeatedDouble_, result.repeatedDouble_);
         }
         if (other.repeatedBool_.Count != 0) {
-          if (result.repeatedBool_.Count == 0) {
-            result.repeatedBool_ = new scg::List<bool>();
-          }
           base.AddRange(other.repeatedBool_, result.repeatedBool_);
         }
         if (other.repeatedString_.Count != 0) {
-          if (result.repeatedString_.Count == 0) {
-            result.repeatedString_ = new scg::List<string>();
-          }
           base.AddRange(other.repeatedString_, result.repeatedString_);
         }
         if (other.repeatedBytes_.Count != 0) {
-          if (result.repeatedBytes_.Count == 0) {
-            result.repeatedBytes_ = new scg::List<pb::ByteString>();
-          }
           base.AddRange(other.repeatedBytes_, result.repeatedBytes_);
         }
         if (other.repeatedGroup_.Count != 0) {
-          if (result.repeatedGroup_.Count == 0) {
-            result.repeatedGroup_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup>();
-          }
           base.AddRange(other.repeatedGroup_, result.repeatedGroup_);
         }
         if (other.repeatedNestedMessage_.Count != 0) {
-          if (result.repeatedNestedMessage_.Count == 0) {
-            result.repeatedNestedMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage>();
-          }
           base.AddRange(other.repeatedNestedMessage_, result.repeatedNestedMessage_);
         }
         if (other.repeatedForeignMessage_.Count != 0) {
-          if (result.repeatedForeignMessage_.Count == 0) {
-            result.repeatedForeignMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
-          }
           base.AddRange(other.repeatedForeignMessage_, result.repeatedForeignMessage_);
         }
         if (other.repeatedImportMessage_.Count != 0) {
-          if (result.repeatedImportMessage_.Count == 0) {
-            result.repeatedImportMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ImportMessage>();
-          }
           base.AddRange(other.repeatedImportMessage_, result.repeatedImportMessage_);
         }
         if (other.repeatedNestedEnum_.Count != 0) {
@@ -3126,15 +3061,9 @@ namespace Google.ProtocolBuffers.TestProtos {
           base.AddRange(other.repeatedImportEnum_, result.repeatedImportEnum_);
         }
         if (other.repeatedStringPiece_.Count != 0) {
-          if (result.repeatedStringPiece_.Count == 0) {
-            result.repeatedStringPiece_ = new scg::List<string>();
-          }
           base.AddRange(other.repeatedStringPiece_, result.repeatedStringPiece_);
         }
         if (other.repeatedCord_.Count != 0) {
-          if (result.repeatedCord_.Count == 0) {
-            result.repeatedCord_ = new scg::List<string>();
-          }
           base.AddRange(other.repeatedCord_, result.repeatedCord_);
         }
         if (other.HasDefaultInt32) {
@@ -4097,7 +4026,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       
       // repeated int32 repeated_int32 = 31;
       public scg::IList<int> RepeatedInt32List {
-        get { return pbc::Lists<int>.AsReadOnly(result.repeatedInt32_); }
+        get { return result.repeatedInt32_; }
       }
       public int RepeatedInt32Count {
         get { return result.RepeatedInt32Count; }
@@ -4110,27 +4039,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedInt32(int value) {
-        if (result.repeatedInt32_.Count == 0) {
-          result.repeatedInt32_ = new scg::List<int>();
-        }
         result.repeatedInt32_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedInt32(scg::IEnumerable<int> values) {
-        if (result.repeatedInt32_.Count == 0) {
-          result.repeatedInt32_ = new scg::List<int>();
-        }
         base.AddRange(values, result.repeatedInt32_);
         return this;
       }
       public Builder ClearRepeatedInt32() {
-        result.repeatedInt32_ = pbc::Lists<int>.Empty;
+        result.repeatedInt32_.Clear();
         return this;
       }
       
       // repeated int64 repeated_int64 = 32;
       public scg::IList<long> RepeatedInt64List {
-        get { return pbc::Lists<long>.AsReadOnly(result.repeatedInt64_); }
+        get { return result.repeatedInt64_; }
       }
       public int RepeatedInt64Count {
         get { return result.RepeatedInt64Count; }
@@ -4143,27 +4066,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedInt64(long value) {
-        if (result.repeatedInt64_.Count == 0) {
-          result.repeatedInt64_ = new scg::List<long>();
-        }
         result.repeatedInt64_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedInt64(scg::IEnumerable<long> values) {
-        if (result.repeatedInt64_.Count == 0) {
-          result.repeatedInt64_ = new scg::List<long>();
-        }
         base.AddRange(values, result.repeatedInt64_);
         return this;
       }
       public Builder ClearRepeatedInt64() {
-        result.repeatedInt64_ = pbc::Lists<long>.Empty;
+        result.repeatedInt64_.Clear();
         return this;
       }
       
       // repeated uint32 repeated_uint32 = 33;
       public scg::IList<uint> RepeatedUint32List {
-        get { return pbc::Lists<uint>.AsReadOnly(result.repeatedUint32_); }
+        get { return result.repeatedUint32_; }
       }
       public int RepeatedUint32Count {
         get { return result.RepeatedUint32Count; }
@@ -4176,27 +4093,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedUint32(uint value) {
-        if (result.repeatedUint32_.Count == 0) {
-          result.repeatedUint32_ = new scg::List<uint>();
-        }
         result.repeatedUint32_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedUint32(scg::IEnumerable<uint> values) {
-        if (result.repeatedUint32_.Count == 0) {
-          result.repeatedUint32_ = new scg::List<uint>();
-        }
         base.AddRange(values, result.repeatedUint32_);
         return this;
       }
       public Builder ClearRepeatedUint32() {
-        result.repeatedUint32_ = pbc::Lists<uint>.Empty;
+        result.repeatedUint32_.Clear();
         return this;
       }
       
       // repeated uint64 repeated_uint64 = 34;
       public scg::IList<ulong> RepeatedUint64List {
-        get { return pbc::Lists<ulong>.AsReadOnly(result.repeatedUint64_); }
+        get { return result.repeatedUint64_; }
       }
       public int RepeatedUint64Count {
         get { return result.RepeatedUint64Count; }
@@ -4209,27 +4120,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedUint64(ulong value) {
-        if (result.repeatedUint64_.Count == 0) {
-          result.repeatedUint64_ = new scg::List<ulong>();
-        }
         result.repeatedUint64_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedUint64(scg::IEnumerable<ulong> values) {
-        if (result.repeatedUint64_.Count == 0) {
-          result.repeatedUint64_ = new scg::List<ulong>();
-        }
         base.AddRange(values, result.repeatedUint64_);
         return this;
       }
       public Builder ClearRepeatedUint64() {
-        result.repeatedUint64_ = pbc::Lists<ulong>.Empty;
+        result.repeatedUint64_.Clear();
         return this;
       }
       
       // repeated sint32 repeated_sint32 = 35;
       public scg::IList<int> RepeatedSint32List {
-        get { return pbc::Lists<int>.AsReadOnly(result.repeatedSint32_); }
+        get { return result.repeatedSint32_; }
       }
       public int RepeatedSint32Count {
         get { return result.RepeatedSint32Count; }
@@ -4242,27 +4147,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedSint32(int value) {
-        if (result.repeatedSint32_.Count == 0) {
-          result.repeatedSint32_ = new scg::List<int>();
-        }
         result.repeatedSint32_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedSint32(scg::IEnumerable<int> values) {
-        if (result.repeatedSint32_.Count == 0) {
-          result.repeatedSint32_ = new scg::List<int>();
-        }
         base.AddRange(values, result.repeatedSint32_);
         return this;
       }
       public Builder ClearRepeatedSint32() {
-        result.repeatedSint32_ = pbc::Lists<int>.Empty;
+        result.repeatedSint32_.Clear();
         return this;
       }
       
       // repeated sint64 repeated_sint64 = 36;
       public scg::IList<long> RepeatedSint64List {
-        get { return pbc::Lists<long>.AsReadOnly(result.repeatedSint64_); }
+        get { return result.repeatedSint64_; }
       }
       public int RepeatedSint64Count {
         get { return result.RepeatedSint64Count; }
@@ -4275,27 +4174,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedSint64(long value) {
-        if (result.repeatedSint64_.Count == 0) {
-          result.repeatedSint64_ = new scg::List<long>();
-        }
         result.repeatedSint64_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedSint64(scg::IEnumerable<long> values) {
-        if (result.repeatedSint64_.Count == 0) {
-          result.repeatedSint64_ = new scg::List<long>();
-        }
         base.AddRange(values, result.repeatedSint64_);
         return this;
       }
       public Builder ClearRepeatedSint64() {
-        result.repeatedSint64_ = pbc::Lists<long>.Empty;
+        result.repeatedSint64_.Clear();
         return this;
       }
       
       // repeated fixed32 repeated_fixed32 = 37;
       public scg::IList<uint> RepeatedFixed32List {
-        get { return pbc::Lists<uint>.AsReadOnly(result.repeatedFixed32_); }
+        get { return result.repeatedFixed32_; }
       }
       public int RepeatedFixed32Count {
         get { return result.RepeatedFixed32Count; }
@@ -4308,27 +4201,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedFixed32(uint value) {
-        if (result.repeatedFixed32_.Count == 0) {
-          result.repeatedFixed32_ = new scg::List<uint>();
-        }
         result.repeatedFixed32_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedFixed32(scg::IEnumerable<uint> values) {
-        if (result.repeatedFixed32_.Count == 0) {
-          result.repeatedFixed32_ = new scg::List<uint>();
-        }
         base.AddRange(values, result.repeatedFixed32_);
         return this;
       }
       public Builder ClearRepeatedFixed32() {
-        result.repeatedFixed32_ = pbc::Lists<uint>.Empty;
+        result.repeatedFixed32_.Clear();
         return this;
       }
       
       // repeated fixed64 repeated_fixed64 = 38;
       public scg::IList<ulong> RepeatedFixed64List {
-        get { return pbc::Lists<ulong>.AsReadOnly(result.repeatedFixed64_); }
+        get { return result.repeatedFixed64_; }
       }
       public int RepeatedFixed64Count {
         get { return result.RepeatedFixed64Count; }
@@ -4341,27 +4228,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedFixed64(ulong value) {
-        if (result.repeatedFixed64_.Count == 0) {
-          result.repeatedFixed64_ = new scg::List<ulong>();
-        }
         result.repeatedFixed64_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedFixed64(scg::IEnumerable<ulong> values) {
-        if (result.repeatedFixed64_.Count == 0) {
-          result.repeatedFixed64_ = new scg::List<ulong>();
-        }
         base.AddRange(values, result.repeatedFixed64_);
         return this;
       }
       public Builder ClearRepeatedFixed64() {
-        result.repeatedFixed64_ = pbc::Lists<ulong>.Empty;
+        result.repeatedFixed64_.Clear();
         return this;
       }
       
       // repeated sfixed32 repeated_sfixed32 = 39;
       public scg::IList<int> RepeatedSfixed32List {
-        get { return pbc::Lists<int>.AsReadOnly(result.repeatedSfixed32_); }
+        get { return result.repeatedSfixed32_; }
       }
       public int RepeatedSfixed32Count {
         get { return result.RepeatedSfixed32Count; }
@@ -4374,27 +4255,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedSfixed32(int value) {
-        if (result.repeatedSfixed32_.Count == 0) {
-          result.repeatedSfixed32_ = new scg::List<int>();
-        }
         result.repeatedSfixed32_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedSfixed32(scg::IEnumerable<int> values) {
-        if (result.repeatedSfixed32_.Count == 0) {
-          result.repeatedSfixed32_ = new scg::List<int>();
-        }
         base.AddRange(values, result.repeatedSfixed32_);
         return this;
       }
       public Builder ClearRepeatedSfixed32() {
-        result.repeatedSfixed32_ = pbc::Lists<int>.Empty;
+        result.repeatedSfixed32_.Clear();
         return this;
       }
       
       // repeated sfixed64 repeated_sfixed64 = 40;
       public scg::IList<long> RepeatedSfixed64List {
-        get { return pbc::Lists<long>.AsReadOnly(result.repeatedSfixed64_); }
+        get { return result.repeatedSfixed64_; }
       }
       public int RepeatedSfixed64Count {
         get { return result.RepeatedSfixed64Count; }
@@ -4407,27 +4282,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedSfixed64(long value) {
-        if (result.repeatedSfixed64_.Count == 0) {
-          result.repeatedSfixed64_ = new scg::List<long>();
-        }
         result.repeatedSfixed64_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedSfixed64(scg::IEnumerable<long> values) {
-        if (result.repeatedSfixed64_.Count == 0) {
-          result.repeatedSfixed64_ = new scg::List<long>();
-        }
         base.AddRange(values, result.repeatedSfixed64_);
         return this;
       }
       public Builder ClearRepeatedSfixed64() {
-        result.repeatedSfixed64_ = pbc::Lists<long>.Empty;
+        result.repeatedSfixed64_.Clear();
         return this;
       }
       
       // repeated float repeated_float = 41;
       public scg::IList<float> RepeatedFloatList {
-        get { return pbc::Lists<float>.AsReadOnly(result.repeatedFloat_); }
+        get { return result.repeatedFloat_; }
       }
       public int RepeatedFloatCount {
         get { return result.RepeatedFloatCount; }
@@ -4440,27 +4309,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedFloat(float value) {
-        if (result.repeatedFloat_.Count == 0) {
-          result.repeatedFloat_ = new scg::List<float>();
-        }
         result.repeatedFloat_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedFloat(scg::IEnumerable<float> values) {
-        if (result.repeatedFloat_.Count == 0) {
-          result.repeatedFloat_ = new scg::List<float>();
-        }
         base.AddRange(values, result.repeatedFloat_);
         return this;
       }
       public Builder ClearRepeatedFloat() {
-        result.repeatedFloat_ = pbc::Lists<float>.Empty;
+        result.repeatedFloat_.Clear();
         return this;
       }
       
       // repeated double repeated_double = 42;
       public scg::IList<double> RepeatedDoubleList {
-        get { return pbc::Lists<double>.AsReadOnly(result.repeatedDouble_); }
+        get { return result.repeatedDouble_; }
       }
       public int RepeatedDoubleCount {
         get { return result.RepeatedDoubleCount; }
@@ -4473,27 +4336,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedDouble(double value) {
-        if (result.repeatedDouble_.Count == 0) {
-          result.repeatedDouble_ = new scg::List<double>();
-        }
         result.repeatedDouble_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedDouble(scg::IEnumerable<double> values) {
-        if (result.repeatedDouble_.Count == 0) {
-          result.repeatedDouble_ = new scg::List<double>();
-        }
         base.AddRange(values, result.repeatedDouble_);
         return this;
       }
       public Builder ClearRepeatedDouble() {
-        result.repeatedDouble_ = pbc::Lists<double>.Empty;
+        result.repeatedDouble_.Clear();
         return this;
       }
       
       // repeated bool repeated_bool = 43;
       public scg::IList<bool> RepeatedBoolList {
-        get { return pbc::Lists<bool>.AsReadOnly(result.repeatedBool_); }
+        get { return result.repeatedBool_; }
       }
       public int RepeatedBoolCount {
         get { return result.RepeatedBoolCount; }
@@ -4506,27 +4363,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedBool(bool value) {
-        if (result.repeatedBool_.Count == 0) {
-          result.repeatedBool_ = new scg::List<bool>();
-        }
         result.repeatedBool_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedBool(scg::IEnumerable<bool> values) {
-        if (result.repeatedBool_.Count == 0) {
-          result.repeatedBool_ = new scg::List<bool>();
-        }
         base.AddRange(values, result.repeatedBool_);
         return this;
       }
       public Builder ClearRepeatedBool() {
-        result.repeatedBool_ = pbc::Lists<bool>.Empty;
+        result.repeatedBool_.Clear();
         return this;
       }
       
       // repeated string repeated_string = 44;
       public scg::IList<string> RepeatedStringList {
-        get { return pbc::Lists<string>.AsReadOnly(result.repeatedString_); }
+        get { return result.repeatedString_; }
       }
       public int RepeatedStringCount {
         get { return result.RepeatedStringCount; }
@@ -4539,27 +4390,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedString(string value) {
-        if (result.repeatedString_.Count == 0) {
-          result.repeatedString_ = new scg::List<string>();
-        }
         result.repeatedString_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedString(scg::IEnumerable<string> values) {
-        if (result.repeatedString_.Count == 0) {
-          result.repeatedString_ = new scg::List<string>();
-        }
         base.AddRange(values, result.repeatedString_);
         return this;
       }
       public Builder ClearRepeatedString() {
-        result.repeatedString_ = pbc::Lists<string>.Empty;
+        result.repeatedString_.Clear();
         return this;
       }
       
       // repeated bytes repeated_bytes = 45;
       public scg::IList<pb::ByteString> RepeatedBytesList {
-        get { return pbc::Lists<pb::ByteString>.AsReadOnly(result.repeatedBytes_); }
+        get { return result.repeatedBytes_; }
       }
       public int RepeatedBytesCount {
         get { return result.RepeatedBytesCount; }
@@ -4572,27 +4417,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedBytes(pb::ByteString value) {
-        if (result.repeatedBytes_.Count == 0) {
-          result.repeatedBytes_ = new scg::List<pb::ByteString>();
-        }
         result.repeatedBytes_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedBytes(scg::IEnumerable<pb::ByteString> values) {
-        if (result.repeatedBytes_.Count == 0) {
-          result.repeatedBytes_ = new scg::List<pb::ByteString>();
-        }
         base.AddRange(values, result.repeatedBytes_);
         return this;
       }
       public Builder ClearRepeatedBytes() {
-        result.repeatedBytes_ = pbc::Lists<pb::ByteString>.Empty;
+        result.repeatedBytes_.Clear();
         return this;
       }
       
       // repeated group RepeatedGroup = 46 {
       public scg::IList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup> RepeatedGroupList {
-        get { return pbc::Lists.AsReadOnly(result.repeatedGroup_); }
+        get { return result.repeatedGroup_; }
       }
       public int RepeatedGroupCount {
         get { return result.RepeatedGroupCount; }
@@ -4609,34 +4448,25 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup value) {
-        if (result.repeatedGroup_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup>.Empty) {
-          result.repeatedGroup_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup>();
-        }
         result.repeatedGroup_.Add(value);
         return this;
       }
       public Builder AddRepeatedGroup(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup.Builder builderForValue) {
-        if (result.repeatedGroup_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup>.Empty) {
-          result.repeatedGroup_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup>();
-        }
         result.repeatedGroup_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeRepeatedGroup(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup> values) {
-        if (result.repeatedGroup_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup>.Empty) {
-          result.repeatedGroup_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup>();
-        }
         base.AddRange(values, result.repeatedGroup_);
         return this;
       }
       public Builder ClearRepeatedGroup() {
-        result.repeatedGroup_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.RepeatedGroup>.Empty;
+        result.repeatedGroup_.Clear();
         return this;
       }
       
       // repeated .protobuf_unittest.TestAllTypes.NestedMessage repeated_nested_message = 48;
       public scg::IList<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage> RepeatedNestedMessageList {
-        get { return pbc::Lists.AsReadOnly(result.repeatedNestedMessage_); }
+        get { return result.repeatedNestedMessage_; }
       }
       public int RepeatedNestedMessageCount {
         get { return result.RepeatedNestedMessageCount; }
@@ -4653,34 +4483,25 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage value) {
-        if (result.repeatedNestedMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage>.Empty) {
-          result.repeatedNestedMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage>();
-        }
         result.repeatedNestedMessage_.Add(value);
         return this;
       }
       public Builder AddRepeatedNestedMessage(global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage.Builder builderForValue) {
-        if (result.repeatedNestedMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage>.Empty) {
-          result.repeatedNestedMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage>();
-        }
         result.repeatedNestedMessage_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeRepeatedNestedMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage> values) {
-        if (result.repeatedNestedMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage>.Empty) {
-          result.repeatedNestedMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage>();
-        }
         base.AddRange(values, result.repeatedNestedMessage_);
         return this;
       }
       public Builder ClearRepeatedNestedMessage() {
-        result.repeatedNestedMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestAllTypes.Types.NestedMessage>.Empty;
+        result.repeatedNestedMessage_.Clear();
         return this;
       }
       
       // repeated .protobuf_unittest.ForeignMessage repeated_foreign_message = 49;
       public scg::IList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> RepeatedForeignMessageList {
-        get { return pbc::Lists.AsReadOnly(result.repeatedForeignMessage_); }
+        get { return result.repeatedForeignMessage_; }
       }
       public int RepeatedForeignMessageCount {
         get { return result.RepeatedForeignMessageCount; }
@@ -4697,34 +4518,25 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {
-        if (result.repeatedForeignMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty) {
-          result.repeatedForeignMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
-        }
         result.repeatedForeignMessage_.Add(value);
         return this;
       }
       public Builder AddRepeatedForeignMessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {
-        if (result.repeatedForeignMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty) {
-          result.repeatedForeignMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
-        }
         result.repeatedForeignMessage_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeRepeatedForeignMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> values) {
-        if (result.repeatedForeignMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty) {
-          result.repeatedForeignMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
-        }
         base.AddRange(values, result.repeatedForeignMessage_);
         return this;
       }
       public Builder ClearRepeatedForeignMessage() {
-        result.repeatedForeignMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty;
+        result.repeatedForeignMessage_.Clear();
         return this;
       }
       
       // repeated .protobuf_unittest_import.ImportMessage repeated_import_message = 50;
       public scg::IList<global::Google.ProtocolBuffers.TestProtos.ImportMessage> RepeatedImportMessageList {
-        get { return pbc::Lists.AsReadOnly(result.repeatedImportMessage_); }
+        get { return result.repeatedImportMessage_; }
       }
       public int RepeatedImportMessageCount {
         get { return result.RepeatedImportMessageCount; }
@@ -4741,28 +4553,19 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessage value) {
-        if (result.repeatedImportMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ImportMessage>.Empty) {
-          result.repeatedImportMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ImportMessage>();
-        }
         result.repeatedImportMessage_.Add(value);
         return this;
       }
       public Builder AddRepeatedImportMessage(global::Google.ProtocolBuffers.TestProtos.ImportMessage.Builder builderForValue) {
-        if (result.repeatedImportMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ImportMessage>.Empty) {
-          result.repeatedImportMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ImportMessage>();
-        }
         result.repeatedImportMessage_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeRepeatedImportMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ImportMessage> values) {
-        if (result.repeatedImportMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ImportMessage>.Empty) {
-          result.repeatedImportMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ImportMessage>();
-        }
         base.AddRange(values, result.repeatedImportMessage_);
         return this;
       }
       public Builder ClearRepeatedImportMessage() {
-        result.repeatedImportMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ImportMessage>.Empty;
+        result.repeatedImportMessage_.Clear();
         return this;
       }
       
@@ -4867,7 +4670,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       
       // repeated string repeated_string_piece = 54 [ctype = STRING_PIECE];
       public scg::IList<string> RepeatedStringPieceList {
-        get { return pbc::Lists<string>.AsReadOnly(result.repeatedStringPiece_); }
+        get { return result.repeatedStringPiece_; }
       }
       public int RepeatedStringPieceCount {
         get { return result.RepeatedStringPieceCount; }
@@ -4880,27 +4683,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedStringPiece(string value) {
-        if (result.repeatedStringPiece_.Count == 0) {
-          result.repeatedStringPiece_ = new scg::List<string>();
-        }
         result.repeatedStringPiece_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedStringPiece(scg::IEnumerable<string> values) {
-        if (result.repeatedStringPiece_.Count == 0) {
-          result.repeatedStringPiece_ = new scg::List<string>();
-        }
         base.AddRange(values, result.repeatedStringPiece_);
         return this;
       }
       public Builder ClearRepeatedStringPiece() {
-        result.repeatedStringPiece_ = pbc::Lists<string>.Empty;
+        result.repeatedStringPiece_.Clear();
         return this;
       }
       
       // repeated string repeated_cord = 55 [ctype = CORD];
       public scg::IList<string> RepeatedCordList {
-        get { return pbc::Lists<string>.AsReadOnly(result.repeatedCord_); }
+        get { return result.repeatedCord_; }
       }
       public int RepeatedCordCount {
         get { return result.RepeatedCordCount; }
@@ -4913,21 +4710,15 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedCord(string value) {
-        if (result.repeatedCord_.Count == 0) {
-          result.repeatedCord_ = new scg::List<string>();
-        }
         result.repeatedCord_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedCord(scg::IEnumerable<string> values) {
-        if (result.repeatedCord_.Count == 0) {
-          result.repeatedCord_ = new scg::List<string>();
-        }
         base.AddRange(values, result.repeatedCord_);
         return this;
       }
       public Builder ClearRepeatedCord() {
-        result.repeatedCord_ = pbc::Lists<string>.Empty;
+        result.repeatedCord_.Clear();
         return this;
       }
       
@@ -5314,7 +5105,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class ForeignMessage : pb::GeneratedMessage<ForeignMessage, ForeignMessage.Builder> {
-    private static readonly ForeignMessage defaultInstance = new ForeignMessage();
+    private static readonly ForeignMessage defaultInstance = new Builder().BuildPartial();
     public static ForeignMessage DefaultInstance {
       get { return defaultInstance; }
     }
@@ -5521,7 +5312,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestAllExtensions : pb::ExtendableMessage<TestAllExtensions, TestAllExtensions.Builder> {
-    private static readonly TestAllExtensions defaultInstance = new TestAllExtensions();
+    private static readonly TestAllExtensions defaultInstance = new Builder().BuildPartial();
     public static TestAllExtensions DefaultInstance {
       get { return defaultInstance; }
     }
@@ -5690,7 +5481,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class OptionalGroup_extension : pb::GeneratedMessage<OptionalGroup_extension, OptionalGroup_extension.Builder> {
-    private static readonly OptionalGroup_extension defaultInstance = new OptionalGroup_extension();
+    private static readonly OptionalGroup_extension defaultInstance = new Builder().BuildPartial();
     public static OptionalGroup_extension DefaultInstance {
       get { return defaultInstance; }
     }
@@ -5897,7 +5688,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class RepeatedGroup_extension : pb::GeneratedMessage<RepeatedGroup_extension, RepeatedGroup_extension.Builder> {
-    private static readonly RepeatedGroup_extension defaultInstance = new RepeatedGroup_extension();
+    private static readonly RepeatedGroup_extension defaultInstance = new Builder().BuildPartial();
     public static RepeatedGroup_extension DefaultInstance {
       get { return defaultInstance; }
     }
@@ -6104,7 +5895,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestRequired : pb::GeneratedMessage<TestRequired, TestRequired.Builder> {
-    private static readonly TestRequired defaultInstance = new TestRequired();
+    private static readonly TestRequired defaultInstance = new Builder().BuildPartial();
     public static TestRequired DefaultInstance {
       get { return defaultInstance; }
     }
@@ -7668,7 +7459,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestRequiredForeign : pb::GeneratedMessage<TestRequiredForeign, TestRequiredForeign.Builder> {
-    private static readonly TestRequiredForeign defaultInstance = new TestRequiredForeign();
+    private static readonly TestRequiredForeign defaultInstance = new Builder().BuildPartial();
     public static TestRequiredForeign DefaultInstance {
       get { return defaultInstance; }
     }
@@ -7700,7 +7491,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated .protobuf_unittest.TestRequired repeated_message = 2;
-    private scg::IList<global::Google.ProtocolBuffers.TestProtos.TestRequired> repeatedMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestRequired>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.TestRequired> repeatedMessage_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.TestRequired>();
     public scg::IList<global::Google.ProtocolBuffers.TestProtos.TestRequired> RepeatedMessageList {
       get { return repeatedMessage_; } 
     }
@@ -7840,9 +7631,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override global::Google.ProtocolBuffers.TestProtos.TestRequiredForeign BuildPartial() {
-        if (result.repeatedMessage_ != pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestRequired>.Empty) {
-          result.repeatedMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestRequired>.AsReadOnly(result.repeatedMessage_);
-        }
+        result.repeatedMessage_.MakeReadOnly();
         global::Google.ProtocolBuffers.TestProtos.TestRequiredForeign returnMe = result;
         result = null;
         return returnMe;
@@ -7863,9 +7652,6 @@ 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.TestRequired>();
-          }
           base.AddRange(other.repeatedMessage_, result.repeatedMessage_);
         }
         if (other.HasDummy) {
@@ -7957,7 +7743,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       
       // repeated .protobuf_unittest.TestRequired repeated_message = 2;
       public scg::IList<global::Google.ProtocolBuffers.TestProtos.TestRequired> RepeatedMessageList {
-        get { return pbc::Lists.AsReadOnly(result.repeatedMessage_); }
+        get { return result.repeatedMessage_; }
       }
       public int RepeatedMessageCount {
         get { return result.RepeatedMessageCount; }
@@ -7974,28 +7760,19 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedMessage(global::Google.ProtocolBuffers.TestProtos.TestRequired value) {
-        if (result.repeatedMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestRequired>.Empty) {
-          result.repeatedMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestRequired>();
-        }
         result.repeatedMessage_.Add(value);
         return this;
       }
       public Builder AddRepeatedMessage(global::Google.ProtocolBuffers.TestProtos.TestRequired.Builder builderForValue) {
-        if (result.repeatedMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestRequired>.Empty) {
-          result.repeatedMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestRequired>();
-        }
         result.repeatedMessage_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeRepeatedMessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.TestRequired> values) {
-        if (result.repeatedMessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestRequired>.Empty) {
-          result.repeatedMessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.TestRequired>();
-        }
         base.AddRange(values, result.repeatedMessage_);
         return this;
       }
       public Builder ClearRepeatedMessage() {
-        result.repeatedMessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.TestRequired>.Empty;
+        result.repeatedMessage_.Clear();
         return this;
       }
       
@@ -8021,7 +7798,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestForeignNested : pb::GeneratedMessage<TestForeignNested, TestForeignNested.Builder> {
-    private static readonly TestForeignNested defaultInstance = new TestForeignNested();
+    private static readonly TestForeignNested defaultInstance = new Builder().BuildPartial();
     public static TestForeignNested DefaultInstance {
       get { return defaultInstance; }
     }
@@ -8249,7 +8026,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestEmptyMessage : pb::GeneratedMessage<TestEmptyMessage, TestEmptyMessage.Builder> {
-    private static readonly TestEmptyMessage defaultInstance = new TestEmptyMessage();
+    private static readonly TestEmptyMessage defaultInstance = new Builder().BuildPartial();
     public static TestEmptyMessage DefaultInstance {
       get { return defaultInstance; }
     }
@@ -8414,7 +8191,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestEmptyMessageWithExtensions : pb::ExtendableMessage<TestEmptyMessageWithExtensions, TestEmptyMessageWithExtensions.Builder> {
-    private static readonly TestEmptyMessageWithExtensions defaultInstance = new TestEmptyMessageWithExtensions();
+    private static readonly TestEmptyMessageWithExtensions defaultInstance = new Builder().BuildPartial();
     public static TestEmptyMessageWithExtensions DefaultInstance {
       get { return defaultInstance; }
     }
@@ -8583,7 +8360,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestReallyLargeTagNumber : pb::GeneratedMessage<TestReallyLargeTagNumber, TestReallyLargeTagNumber.Builder> {
-    private static readonly TestReallyLargeTagNumber defaultInstance = new TestReallyLargeTagNumber();
+    private static readonly TestReallyLargeTagNumber defaultInstance = new Builder().BuildPartial();
     public static TestReallyLargeTagNumber DefaultInstance {
       get { return defaultInstance; }
     }
@@ -8832,7 +8609,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestRecursiveMessage : pb::GeneratedMessage<TestRecursiveMessage, TestRecursiveMessage.Builder> {
-    private static readonly TestRecursiveMessage defaultInstance = new TestRecursiveMessage();
+    private static readonly TestRecursiveMessage defaultInstance = new Builder().BuildPartial();
     public static TestRecursiveMessage DefaultInstance {
       get { return defaultInstance; }
     }
@@ -9102,7 +8879,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestMutualRecursionA : pb::GeneratedMessage<TestMutualRecursionA, TestMutualRecursionA.Builder> {
-    private static readonly TestMutualRecursionA defaultInstance = new TestMutualRecursionA();
+    private static readonly TestMutualRecursionA defaultInstance = new Builder().BuildPartial();
     public static TestMutualRecursionA DefaultInstance {
       get { return defaultInstance; }
     }
@@ -9330,7 +9107,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestMutualRecursionB : pb::GeneratedMessage<TestMutualRecursionB, TestMutualRecursionB.Builder> {
-    private static readonly TestMutualRecursionB defaultInstance = new TestMutualRecursionB();
+    private static readonly TestMutualRecursionB defaultInstance = new Builder().BuildPartial();
     public static TestMutualRecursionB DefaultInstance {
       get { return defaultInstance; }
     }
@@ -9600,7 +9377,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestDupFieldNumber : pb::GeneratedMessage<TestDupFieldNumber, TestDupFieldNumber.Builder> {
-    private static readonly TestDupFieldNumber defaultInstance = new TestDupFieldNumber();
+    private static readonly TestDupFieldNumber defaultInstance = new Builder().BuildPartial();
     public static TestDupFieldNumber DefaultInstance {
       get { return defaultInstance; }
     }
@@ -9624,7 +9401,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     #region Nested types
     public static class Types {
       public sealed partial class Foo : pb::GeneratedMessage<Foo, Foo.Builder> {
-        private static readonly Foo defaultInstance = new Foo();
+        private static readonly Foo defaultInstance = new Builder().BuildPartial();
         public static Foo DefaultInstance {
           get { return defaultInstance; }
         }
@@ -9831,7 +9608,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public sealed partial class Bar : pb::GeneratedMessage<Bar, Bar.Builder> {
-        private static readonly Bar defaultInstance = new Bar();
+        private static readonly Bar defaultInstance = new Builder().BuildPartial();
         public static Bar DefaultInstance {
           get { return defaultInstance; }
         }
@@ -10352,7 +10129,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestNestedMessageHasBits : pb::GeneratedMessage<TestNestedMessageHasBits, TestNestedMessageHasBits.Builder> {
-    private static readonly TestNestedMessageHasBits defaultInstance = new TestNestedMessageHasBits();
+    private static readonly TestNestedMessageHasBits defaultInstance = new Builder().BuildPartial();
     public static TestNestedMessageHasBits DefaultInstance {
       get { return defaultInstance; }
     }
@@ -10376,7 +10153,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     #region Nested types
     public static class Types {
       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; }
         }
@@ -10398,9 +10175,9 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         // repeated int32 nestedmessage_repeated_int32 = 1;
-        private scg::IList<int> nestedmessageRepeatedInt32_ = pbc::Lists<int>.Empty;
+        private pbc::PopsicleList<int> nestedmessageRepeatedInt32_ = new pbc::PopsicleList<int>();
         public scg::IList<int> NestedmessageRepeatedInt32List {
-          get { return nestedmessageRepeatedInt32_; }
+          get { return nestedmessageRepeatedInt32_; } 
         }
         public int NestedmessageRepeatedInt32Count {
           get { return nestedmessageRepeatedInt32_.Count; }
@@ -10410,7 +10187,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         // repeated .protobuf_unittest.ForeignMessage nestedmessage_repeated_foreignmessage = 2;
-        private scg::IList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> nestedmessageRepeatedForeignmessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty;
+        private pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> nestedmessageRepeatedForeignmessage_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
         public scg::IList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> NestedmessageRepeatedForeignmessageList {
           get { return nestedmessageRepeatedForeignmessage_; } 
         }
@@ -10529,10 +10306,8 @@ namespace Google.ProtocolBuffers.TestProtos {
           }
           
           public override global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage BuildPartial() {
-            result.nestedmessageRepeatedInt32_ = pbc::Lists<int>.AsReadOnly(result.nestedmessageRepeatedInt32_);
-            if (result.nestedmessageRepeatedForeignmessage_ != pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty) {
-              result.nestedmessageRepeatedForeignmessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.AsReadOnly(result.nestedmessageRepeatedForeignmessage_);
-            }
+            result.nestedmessageRepeatedInt32_.MakeReadOnly();
+            result.nestedmessageRepeatedForeignmessage_.MakeReadOnly();
             global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage returnMe = result;
             result = null;
             return returnMe;
@@ -10550,15 +10325,9 @@ namespace Google.ProtocolBuffers.TestProtos {
           public override Builder MergeFrom(global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage other) {
             if (other == global::Google.ProtocolBuffers.TestProtos.TestNestedMessageHasBits.Types.NestedMessage.DefaultInstance) return this;
             if (other.nestedmessageRepeatedInt32_.Count != 0) {
-              if (result.nestedmessageRepeatedInt32_.Count == 0) {
-                result.nestedmessageRepeatedInt32_ = new scg::List<int>();
-              }
               base.AddRange(other.nestedmessageRepeatedInt32_, result.nestedmessageRepeatedInt32_);
             }
             if (other.nestedmessageRepeatedForeignmessage_.Count != 0) {
-              if (result.nestedmessageRepeatedForeignmessage_.Count == 0) {
-                result.nestedmessageRepeatedForeignmessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
-              }
               base.AddRange(other.nestedmessageRepeatedForeignmessage_, result.nestedmessageRepeatedForeignmessage_);
             }
             this.MergeUnknownFields(other.UnknownFields);
@@ -10603,7 +10372,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           
           // repeated int32 nestedmessage_repeated_int32 = 1;
           public scg::IList<int> NestedmessageRepeatedInt32List {
-            get { return pbc::Lists<int>.AsReadOnly(result.nestedmessageRepeatedInt32_); }
+            get { return result.nestedmessageRepeatedInt32_; }
           }
           public int NestedmessageRepeatedInt32Count {
             get { return result.NestedmessageRepeatedInt32Count; }
@@ -10616,27 +10385,21 @@ namespace Google.ProtocolBuffers.TestProtos {
             return this;
           }
           public Builder AddNestedmessageRepeatedInt32(int value) {
-            if (result.nestedmessageRepeatedInt32_.Count == 0) {
-              result.nestedmessageRepeatedInt32_ = new scg::List<int>();
-            }
             result.nestedmessageRepeatedInt32_.Add(value);
             return this;
           }
           public Builder AddRangeNestedmessageRepeatedInt32(scg::IEnumerable<int> values) {
-            if (result.nestedmessageRepeatedInt32_.Count == 0) {
-              result.nestedmessageRepeatedInt32_ = new scg::List<int>();
-            }
             base.AddRange(values, result.nestedmessageRepeatedInt32_);
             return this;
           }
           public Builder ClearNestedmessageRepeatedInt32() {
-            result.nestedmessageRepeatedInt32_ = pbc::Lists<int>.Empty;
+            result.nestedmessageRepeatedInt32_.Clear();
             return this;
           }
           
           // repeated .protobuf_unittest.ForeignMessage nestedmessage_repeated_foreignmessage = 2;
           public scg::IList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> NestedmessageRepeatedForeignmessageList {
-            get { return pbc::Lists.AsReadOnly(result.nestedmessageRepeatedForeignmessage_); }
+            get { return result.nestedmessageRepeatedForeignmessage_; }
           }
           public int NestedmessageRepeatedForeignmessageCount {
             get { return result.NestedmessageRepeatedForeignmessageCount; }
@@ -10653,28 +10416,19 @@ namespace Google.ProtocolBuffers.TestProtos {
             return this;
           }
           public Builder AddNestedmessageRepeatedForeignmessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {
-            if (result.nestedmessageRepeatedForeignmessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty) {
-              result.nestedmessageRepeatedForeignmessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
-            }
             result.nestedmessageRepeatedForeignmessage_.Add(value);
             return this;
           }
           public Builder AddNestedmessageRepeatedForeignmessage(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {
-            if (result.nestedmessageRepeatedForeignmessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty) {
-              result.nestedmessageRepeatedForeignmessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
-            }
             result.nestedmessageRepeatedForeignmessage_.Add(builderForValue.Build());
             return this;
           }
           public Builder AddRangeNestedmessageRepeatedForeignmessage(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> values) {
-            if (result.nestedmessageRepeatedForeignmessage_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty) {
-              result.nestedmessageRepeatedForeignmessage_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
-            }
             base.AddRange(values, result.nestedmessageRepeatedForeignmessage_);
             return this;
           }
           public Builder ClearNestedmessageRepeatedForeignmessage() {
-            result.nestedmessageRepeatedForeignmessage_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty;
+            result.nestedmessageRepeatedForeignmessage_.Clear();
             return this;
           }
         }
@@ -10890,7 +10644,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestCamelCaseFieldNames : pb::GeneratedMessage<TestCamelCaseFieldNames, TestCamelCaseFieldNames.Builder> {
-    private static readonly TestCamelCaseFieldNames defaultInstance = new TestCamelCaseFieldNames();
+    private static readonly TestCamelCaseFieldNames defaultInstance = new Builder().BuildPartial();
     public static TestCamelCaseFieldNames DefaultInstance {
       get { return defaultInstance; }
     }
@@ -10970,9 +10724,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated int32 RepeatedPrimitiveField = 7;
-    private scg::IList<int> repeatedPrimitiveField_ = pbc::Lists<int>.Empty;
+    private pbc::PopsicleList<int> repeatedPrimitiveField_ = new pbc::PopsicleList<int>();
     public scg::IList<int> RepeatedPrimitiveFieldList {
-      get { return repeatedPrimitiveField_; }
+      get { return repeatedPrimitiveField_; } 
     }
     public int RepeatedPrimitiveFieldCount {
       get { return repeatedPrimitiveField_.Count; }
@@ -10982,9 +10736,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated string RepeatedStringField = 8;
-    private scg::IList<string> repeatedStringField_ = pbc::Lists<string>.Empty;
+    private pbc::PopsicleList<string> repeatedStringField_ = new pbc::PopsicleList<string>();
     public scg::IList<string> RepeatedStringFieldList {
-      get { return repeatedStringField_; }
+      get { return repeatedStringField_; } 
     }
     public int RepeatedStringFieldCount {
       get { return repeatedStringField_.Count; }
@@ -11006,7 +10760,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated .protobuf_unittest.ForeignMessage RepeatedMessageField = 10;
-    private scg::IList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> repeatedMessageField_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> repeatedMessageField_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
     public scg::IList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> RepeatedMessageFieldList {
       get { return repeatedMessageField_; } 
     }
@@ -11018,9 +10772,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated string RepeatedStringPieceField = 11 [ctype = STRING_PIECE];
-    private scg::IList<string> repeatedStringPieceField_ = pbc::Lists<string>.Empty;
+    private pbc::PopsicleList<string> repeatedStringPieceField_ = new pbc::PopsicleList<string>();
     public scg::IList<string> RepeatedStringPieceFieldList {
-      get { return repeatedStringPieceField_; }
+      get { return repeatedStringPieceField_; } 
     }
     public int RepeatedStringPieceFieldCount {
       get { return repeatedStringPieceField_.Count; }
@@ -11030,9 +10784,9 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     // repeated string RepeatedCordField = 12 [ctype = CORD];
-    private scg::IList<string> repeatedCordField_ = pbc::Lists<string>.Empty;
+    private pbc::PopsicleList<string> repeatedCordField_ = new pbc::PopsicleList<string>();
     public scg::IList<string> RepeatedCordFieldList {
-      get { return repeatedCordField_; }
+      get { return repeatedCordField_; } 
     }
     public int RepeatedCordFieldCount {
       get { return repeatedCordField_.Count; }
@@ -11214,14 +10968,12 @@ namespace Google.ProtocolBuffers.TestProtos {
       }
       
       public override global::Google.ProtocolBuffers.TestProtos.TestCamelCaseFieldNames BuildPartial() {
-        result.repeatedPrimitiveField_ = pbc::Lists<int>.AsReadOnly(result.repeatedPrimitiveField_);
-        result.repeatedStringField_ = pbc::Lists<string>.AsReadOnly(result.repeatedStringField_);
+        result.repeatedPrimitiveField_.MakeReadOnly();
+        result.repeatedStringField_.MakeReadOnly();
         result.repeatedEnumField_ = pbc::Lists.AsReadOnly(result.repeatedEnumField_);
-        if (result.repeatedMessageField_ != pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty) {
-          result.repeatedMessageField_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.AsReadOnly(result.repeatedMessageField_);
-        }
-        result.repeatedStringPieceField_ = pbc::Lists<string>.AsReadOnly(result.repeatedStringPieceField_);
-        result.repeatedCordField_ = pbc::Lists<string>.AsReadOnly(result.repeatedCordField_);
+        result.repeatedMessageField_.MakeReadOnly();
+        result.repeatedStringPieceField_.MakeReadOnly();
+        result.repeatedCordField_.MakeReadOnly();
         global::Google.ProtocolBuffers.TestProtos.TestCamelCaseFieldNames returnMe = result;
         result = null;
         return returnMe;
@@ -11257,15 +11009,9 @@ namespace Google.ProtocolBuffers.TestProtos {
           CordField = other.CordField;
         }
         if (other.repeatedPrimitiveField_.Count != 0) {
-          if (result.repeatedPrimitiveField_.Count == 0) {
-            result.repeatedPrimitiveField_ = new scg::List<int>();
-          }
           base.AddRange(other.repeatedPrimitiveField_, result.repeatedPrimitiveField_);
         }
         if (other.repeatedStringField_.Count != 0) {
-          if (result.repeatedStringField_.Count == 0) {
-            result.repeatedStringField_ = new scg::List<string>();
-          }
           base.AddRange(other.repeatedStringField_, result.repeatedStringField_);
         }
         if (other.repeatedEnumField_.Count != 0) {
@@ -11275,21 +11021,12 @@ namespace Google.ProtocolBuffers.TestProtos {
           base.AddRange(other.repeatedEnumField_, result.repeatedEnumField_);
         }
         if (other.repeatedMessageField_.Count != 0) {
-          if (result.repeatedMessageField_.Count == 0) {
-            result.repeatedMessageField_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
-          }
           base.AddRange(other.repeatedMessageField_, result.repeatedMessageField_);
         }
         if (other.repeatedStringPieceField_.Count != 0) {
-          if (result.repeatedStringPieceField_.Count == 0) {
-            result.repeatedStringPieceField_ = new scg::List<string>();
-          }
           base.AddRange(other.repeatedStringPieceField_, result.repeatedStringPieceField_);
         }
         if (other.repeatedCordField_.Count != 0) {
-          if (result.repeatedCordField_.Count == 0) {
-            result.repeatedCordField_ = new scg::List<string>();
-          }
           base.AddRange(other.repeatedCordField_, result.repeatedCordField_);
         }
         this.MergeUnknownFields(other.UnknownFields);
@@ -11520,7 +11257,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       
       // repeated int32 RepeatedPrimitiveField = 7;
       public scg::IList<int> RepeatedPrimitiveFieldList {
-        get { return pbc::Lists<int>.AsReadOnly(result.repeatedPrimitiveField_); }
+        get { return result.repeatedPrimitiveField_; }
       }
       public int RepeatedPrimitiveFieldCount {
         get { return result.RepeatedPrimitiveFieldCount; }
@@ -11533,27 +11270,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedPrimitiveField(int value) {
-        if (result.repeatedPrimitiveField_.Count == 0) {
-          result.repeatedPrimitiveField_ = new scg::List<int>();
-        }
         result.repeatedPrimitiveField_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedPrimitiveField(scg::IEnumerable<int> values) {
-        if (result.repeatedPrimitiveField_.Count == 0) {
-          result.repeatedPrimitiveField_ = new scg::List<int>();
-        }
         base.AddRange(values, result.repeatedPrimitiveField_);
         return this;
       }
       public Builder ClearRepeatedPrimitiveField() {
-        result.repeatedPrimitiveField_ = pbc::Lists<int>.Empty;
+        result.repeatedPrimitiveField_.Clear();
         return this;
       }
       
       // repeated string RepeatedStringField = 8;
       public scg::IList<string> RepeatedStringFieldList {
-        get { return pbc::Lists<string>.AsReadOnly(result.repeatedStringField_); }
+        get { return result.repeatedStringField_; }
       }
       public int RepeatedStringFieldCount {
         get { return result.RepeatedStringFieldCount; }
@@ -11566,21 +11297,15 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedStringField(string value) {
-        if (result.repeatedStringField_.Count == 0) {
-          result.repeatedStringField_ = new scg::List<string>();
-        }
         result.repeatedStringField_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedStringField(scg::IEnumerable<string> values) {
-        if (result.repeatedStringField_.Count == 0) {
-          result.repeatedStringField_ = new scg::List<string>();
-        }
         base.AddRange(values, result.repeatedStringField_);
         return this;
       }
       public Builder ClearRepeatedStringField() {
-        result.repeatedStringField_ = pbc::Lists<string>.Empty;
+        result.repeatedStringField_.Clear();
         return this;
       }
       
@@ -11619,7 +11344,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       
       // repeated .protobuf_unittest.ForeignMessage RepeatedMessageField = 10;
       public scg::IList<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> RepeatedMessageFieldList {
-        get { return pbc::Lists.AsReadOnly(result.repeatedMessageField_); }
+        get { return result.repeatedMessageField_; }
       }
       public int RepeatedMessageFieldCount {
         get { return result.RepeatedMessageFieldCount; }
@@ -11636,34 +11361,25 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedMessageField(global::Google.ProtocolBuffers.TestProtos.ForeignMessage value) {
-        if (result.repeatedMessageField_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty) {
-          result.repeatedMessageField_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
-        }
         result.repeatedMessageField_.Add(value);
         return this;
       }
       public Builder AddRepeatedMessageField(global::Google.ProtocolBuffers.TestProtos.ForeignMessage.Builder builderForValue) {
-        if (result.repeatedMessageField_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty) {
-          result.repeatedMessageField_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
-        }
         result.repeatedMessageField_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeRepeatedMessageField(scg::IEnumerable<global::Google.ProtocolBuffers.TestProtos.ForeignMessage> values) {
-        if (result.repeatedMessageField_ == pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty) {
-          result.repeatedMessageField_ = new scg::List<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>();
-        }
         base.AddRange(values, result.repeatedMessageField_);
         return this;
       }
       public Builder ClearRepeatedMessageField() {
-        result.repeatedMessageField_ = pbc::Lists<global::Google.ProtocolBuffers.TestProtos.ForeignMessage>.Empty;
+        result.repeatedMessageField_.Clear();
         return this;
       }
       
       // repeated string RepeatedStringPieceField = 11 [ctype = STRING_PIECE];
       public scg::IList<string> RepeatedStringPieceFieldList {
-        get { return pbc::Lists<string>.AsReadOnly(result.repeatedStringPieceField_); }
+        get { return result.repeatedStringPieceField_; }
       }
       public int RepeatedStringPieceFieldCount {
         get { return result.RepeatedStringPieceFieldCount; }
@@ -11676,27 +11392,21 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedStringPieceField(string value) {
-        if (result.repeatedStringPieceField_.Count == 0) {
-          result.repeatedStringPieceField_ = new scg::List<string>();
-        }
         result.repeatedStringPieceField_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedStringPieceField(scg::IEnumerable<string> values) {
-        if (result.repeatedStringPieceField_.Count == 0) {
-          result.repeatedStringPieceField_ = new scg::List<string>();
-        }
         base.AddRange(values, result.repeatedStringPieceField_);
         return this;
       }
       public Builder ClearRepeatedStringPieceField() {
-        result.repeatedStringPieceField_ = pbc::Lists<string>.Empty;
+        result.repeatedStringPieceField_.Clear();
         return this;
       }
       
       // repeated string RepeatedCordField = 12 [ctype = CORD];
       public scg::IList<string> RepeatedCordFieldList {
-        get { return pbc::Lists<string>.AsReadOnly(result.repeatedCordField_); }
+        get { return result.repeatedCordField_; }
       }
       public int RepeatedCordFieldCount {
         get { return result.RepeatedCordFieldCount; }
@@ -11709,28 +11419,22 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       public Builder AddRepeatedCordField(string value) {
-        if (result.repeatedCordField_.Count == 0) {
-          result.repeatedCordField_ = new scg::List<string>();
-        }
         result.repeatedCordField_.Add(value);
         return this;
       }
       public Builder AddRangeRepeatedCordField(scg::IEnumerable<string> values) {
-        if (result.repeatedCordField_.Count == 0) {
-          result.repeatedCordField_ = new scg::List<string>();
-        }
         base.AddRange(values, result.repeatedCordField_);
         return this;
       }
       public Builder ClearRepeatedCordField() {
-        result.repeatedCordField_ = pbc::Lists<string>.Empty;
+        result.repeatedCordField_.Clear();
         return this;
       }
     }
   }
   
   public sealed partial class TestFieldOrderings : pb::ExtendableMessage<TestFieldOrderings, TestFieldOrderings.Builder> {
-    private static readonly TestFieldOrderings defaultInstance = new TestFieldOrderings();
+    private static readonly TestFieldOrderings defaultInstance = new Builder().BuildPartial();
     public static TestFieldOrderings DefaultInstance {
       get { return defaultInstance; }
     }
@@ -12026,7 +11730,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class TestExtremeDefaultValues : pb::GeneratedMessage<TestExtremeDefaultValues, TestExtremeDefaultValues.Builder> {
-    private static readonly TestExtremeDefaultValues defaultInstance = new TestExtremeDefaultValues();
+    private static readonly TestExtremeDefaultValues defaultInstance = new Builder().BuildPartial();
     public static TestExtremeDefaultValues DefaultInstance {
       get { return defaultInstance; }
     }
@@ -12443,7 +12147,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class FooRequest : pb::GeneratedMessage<FooRequest, FooRequest.Builder> {
-    private static readonly FooRequest defaultInstance = new FooRequest();
+    private static readonly FooRequest defaultInstance = new Builder().BuildPartial();
     public static FooRequest DefaultInstance {
       get { return defaultInstance; }
     }
@@ -12608,7 +12312,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class FooResponse : pb::GeneratedMessage<FooResponse, FooResponse.Builder> {
-    private static readonly FooResponse defaultInstance = new FooResponse();
+    private static readonly FooResponse defaultInstance = new Builder().BuildPartial();
     public static FooResponse DefaultInstance {
       get { return defaultInstance; }
     }
@@ -12773,7 +12477,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class BarRequest : pb::GeneratedMessage<BarRequest, BarRequest.Builder> {
-    private static readonly BarRequest defaultInstance = new BarRequest();
+    private static readonly BarRequest defaultInstance = new Builder().BuildPartial();
     public static BarRequest DefaultInstance {
       get { return defaultInstance; }
     }
@@ -12938,7 +12642,7 @@ namespace Google.ProtocolBuffers.TestProtos {
   }
   
   public sealed partial class BarResponse : pb::GeneratedMessage<BarResponse, BarResponse.Builder> {
-    private static readonly BarResponse defaultInstance = new BarResponse();
+    private static readonly BarResponse defaultInstance = new Builder().BuildPartial();
     public static BarResponse DefaultInstance {
       get { return defaultInstance; }
     }
diff --git a/csharp/ProtocolBuffers/Collections/PopsicleList.cs b/csharp/ProtocolBuffers/Collections/PopsicleList.cs
new file mode 100644
index 00000000..4efe13d0
--- /dev/null
+++ b/csharp/ProtocolBuffers/Collections/PopsicleList.cs
@@ -0,0 +1,95 @@
+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");
+      }
+    }
+  }
+}
diff --git a/csharp/ProtocolBuffers/Delegates.cs b/csharp/ProtocolBuffers/Delegates.cs
index 2aa440b1..08774019 100644
--- a/csharp/ProtocolBuffers/Delegates.cs
+++ b/csharp/ProtocolBuffers/Delegates.cs
@@ -1,8 +1,32 @@
-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);
 }
diff --git a/csharp/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs b/csharp/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
index e42c36f3..488b0c60 100644
--- a/csharp/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
+++ b/csharp/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
@@ -255,7 +255,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
   
   #region Messages
   public sealed partial class FileDescriptorSet : pb::GeneratedMessage<FileDescriptorSet, FileDescriptorSet.Builder> {
-    private static readonly FileDescriptorSet defaultInstance = new FileDescriptorSet();
+    private static readonly FileDescriptorSet defaultInstance = new Builder().BuildPartial();
     public static FileDescriptorSet DefaultInstance {
       get { return defaultInstance; }
     }
@@ -277,7 +277,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     // repeated .google.protobuf.FileDescriptorProto file = 1;
-    private scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto> file_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto> file_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto>();
     public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto> FileList {
       get { return file_; } 
     }
@@ -389,9 +389,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }
       
       public override global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorSet BuildPartial() {
-        if (result.file_ != pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto>.Empty) {
-          result.file_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto>.AsReadOnly(result.file_);
-        }
+        result.file_.MakeReadOnly();
         global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorSet returnMe = result;
         result = null;
         return returnMe;
@@ -409,9 +407,6 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       public override Builder MergeFrom(global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorSet other) {
         if (other == global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorSet.DefaultInstance) return this;
         if (other.file_.Count != 0) {
-          if (result.file_.Count == 0) {
-            result.file_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto>();
-          }
           base.AddRange(other.file_, result.file_);
         }
         this.MergeUnknownFields(other.UnknownFields);
@@ -452,7 +447,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       
       // repeated .google.protobuf.FileDescriptorProto file = 1;
       public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto> FileList {
-        get { return pbc::Lists.AsReadOnly(result.file_); }
+        get { return result.file_; }
       }
       public int FileCount {
         get { return result.FileCount; }
@@ -469,35 +464,26 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       public Builder AddFile(global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto value) {
-        if (result.file_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto>.Empty) {
-          result.file_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto>();
-        }
         result.file_.Add(value);
         return this;
       }
       public Builder AddFile(global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto.Builder builderForValue) {
-        if (result.file_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto>.Empty) {
-          result.file_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto>();
-        }
         result.file_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeFile(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto> values) {
-        if (result.file_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto>.Empty) {
-          result.file_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto>();
-        }
         base.AddRange(values, result.file_);
         return this;
       }
       public Builder ClearFile() {
-        result.file_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto>.Empty;
+        result.file_.Clear();
         return this;
       }
     }
   }
   
   public sealed partial class FileDescriptorProto : pb::GeneratedMessage<FileDescriptorProto, FileDescriptorProto.Builder> {
-    private static readonly FileDescriptorProto defaultInstance = new FileDescriptorProto();
+    private static readonly FileDescriptorProto defaultInstance = new Builder().BuildPartial();
     public static FileDescriptorProto DefaultInstance {
       get { return defaultInstance; }
     }
@@ -539,9 +525,9 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     // repeated string dependency = 3;
-    private scg::IList<string> dependency_ = pbc::Lists<string>.Empty;
+    private pbc::PopsicleList<string> dependency_ = new pbc::PopsicleList<string>();
     public scg::IList<string> DependencyList {
-      get { return dependency_; }
+      get { return dependency_; } 
     }
     public int DependencyCount {
       get { return dependency_.Count; }
@@ -551,7 +537,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     // repeated .google.protobuf.DescriptorProto message_type = 4;
-    private scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto> messageType_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto> messageType_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>();
     public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto> MessageTypeList {
       get { return messageType_; } 
     }
@@ -563,7 +549,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     // repeated .google.protobuf.EnumDescriptorProto enum_type = 5;
-    private scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto> enumType_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto> enumType_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>();
     public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto> EnumTypeList {
       get { return enumType_; } 
     }
@@ -575,7 +561,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     // repeated .google.protobuf.ServiceDescriptorProto service = 6;
-    private scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto> service_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto> service_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto>();
     public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto> ServiceList {
       get { return service_; } 
     }
@@ -587,7 +573,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     // repeated .google.protobuf.FieldDescriptorProto extension = 7;
-    private scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> extension_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> extension_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
     public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> ExtensionList {
       get { return extension_; } 
     }
@@ -752,19 +738,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }
       
       public override global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto BuildPartial() {
-        result.dependency_ = pbc::Lists<string>.AsReadOnly(result.dependency_);
-        if (result.messageType_ != pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>.Empty) {
-          result.messageType_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>.AsReadOnly(result.messageType_);
-        }
-        if (result.enumType_ != pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>.Empty) {
-          result.enumType_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>.AsReadOnly(result.enumType_);
-        }
-        if (result.service_ != pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto>.Empty) {
-          result.service_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto>.AsReadOnly(result.service_);
-        }
-        if (result.extension_ != pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty) {
-          result.extension_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.AsReadOnly(result.extension_);
-        }
+        result.dependency_.MakeReadOnly();
+        result.messageType_.MakeReadOnly();
+        result.enumType_.MakeReadOnly();
+        result.service_.MakeReadOnly();
+        result.extension_.MakeReadOnly();
         global::Google.ProtocolBuffers.DescriptorProtos.FileDescriptorProto returnMe = result;
         result = null;
         return returnMe;
@@ -788,33 +766,18 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           Package = other.Package;
         }
         if (other.dependency_.Count != 0) {
-          if (result.dependency_.Count == 0) {
-            result.dependency_ = new scg::List<string>();
-          }
           base.AddRange(other.dependency_, result.dependency_);
         }
         if (other.messageType_.Count != 0) {
-          if (result.messageType_.Count == 0) {
-            result.messageType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>();
-          }
           base.AddRange(other.messageType_, result.messageType_);
         }
         if (other.enumType_.Count != 0) {
-          if (result.enumType_.Count == 0) {
-            result.enumType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>();
-          }
           base.AddRange(other.enumType_, result.enumType_);
         }
         if (other.service_.Count != 0) {
-          if (result.service_.Count == 0) {
-            result.service_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto>();
-          }
           base.AddRange(other.service_, result.service_);
         }
         if (other.extension_.Count != 0) {
-          if (result.extension_.Count == 0) {
-            result.extension_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
-          }
           base.AddRange(other.extension_, result.extension_);
         }
         if (other.HasOptions) {
@@ -935,7 +898,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       
       // repeated string dependency = 3;
       public scg::IList<string> DependencyList {
-        get { return pbc::Lists<string>.AsReadOnly(result.dependency_); }
+        get { return result.dependency_; }
       }
       public int DependencyCount {
         get { return result.DependencyCount; }
@@ -948,27 +911,21 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       public Builder AddDependency(string value) {
-        if (result.dependency_.Count == 0) {
-          result.dependency_ = new scg::List<string>();
-        }
         result.dependency_.Add(value);
         return this;
       }
       public Builder AddRangeDependency(scg::IEnumerable<string> values) {
-        if (result.dependency_.Count == 0) {
-          result.dependency_ = new scg::List<string>();
-        }
         base.AddRange(values, result.dependency_);
         return this;
       }
       public Builder ClearDependency() {
-        result.dependency_ = pbc::Lists<string>.Empty;
+        result.dependency_.Clear();
         return this;
       }
       
       // repeated .google.protobuf.DescriptorProto message_type = 4;
       public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto> MessageTypeList {
-        get { return pbc::Lists.AsReadOnly(result.messageType_); }
+        get { return result.messageType_; }
       }
       public int MessageTypeCount {
         get { return result.MessageTypeCount; }
@@ -985,34 +942,25 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       public Builder AddMessageType(global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto value) {
-        if (result.messageType_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>.Empty) {
-          result.messageType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>();
-        }
         result.messageType_.Add(value);
         return this;
       }
       public Builder AddMessageType(global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Builder builderForValue) {
-        if (result.messageType_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>.Empty) {
-          result.messageType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>();
-        }
         result.messageType_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeMessageType(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto> values) {
-        if (result.messageType_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>.Empty) {
-          result.messageType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>();
-        }
         base.AddRange(values, result.messageType_);
         return this;
       }
       public Builder ClearMessageType() {
-        result.messageType_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>.Empty;
+        result.messageType_.Clear();
         return this;
       }
       
       // repeated .google.protobuf.EnumDescriptorProto enum_type = 5;
       public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto> EnumTypeList {
-        get { return pbc::Lists.AsReadOnly(result.enumType_); }
+        get { return result.enumType_; }
       }
       public int EnumTypeCount {
         get { return result.EnumTypeCount; }
@@ -1029,34 +977,25 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       public Builder AddEnumType(global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto value) {
-        if (result.enumType_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>.Empty) {
-          result.enumType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>();
-        }
         result.enumType_.Add(value);
         return this;
       }
       public Builder AddEnumType(global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto.Builder builderForValue) {
-        if (result.enumType_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>.Empty) {
-          result.enumType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>();
-        }
         result.enumType_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeEnumType(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto> values) {
-        if (result.enumType_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>.Empty) {
-          result.enumType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>();
-        }
         base.AddRange(values, result.enumType_);
         return this;
       }
       public Builder ClearEnumType() {
-        result.enumType_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>.Empty;
+        result.enumType_.Clear();
         return this;
       }
       
       // repeated .google.protobuf.ServiceDescriptorProto service = 6;
       public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto> ServiceList {
-        get { return pbc::Lists.AsReadOnly(result.service_); }
+        get { return result.service_; }
       }
       public int ServiceCount {
         get { return result.ServiceCount; }
@@ -1073,34 +1012,25 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       public Builder AddService(global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto value) {
-        if (result.service_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto>.Empty) {
-          result.service_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto>();
-        }
         result.service_.Add(value);
         return this;
       }
       public Builder AddService(global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto.Builder builderForValue) {
-        if (result.service_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto>.Empty) {
-          result.service_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto>();
-        }
         result.service_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeService(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto> values) {
-        if (result.service_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto>.Empty) {
-          result.service_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto>();
-        }
         base.AddRange(values, result.service_);
         return this;
       }
       public Builder ClearService() {
-        result.service_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto>.Empty;
+        result.service_.Clear();
         return this;
       }
       
       // repeated .google.protobuf.FieldDescriptorProto extension = 7;
       public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> ExtensionList {
-        get { return pbc::Lists.AsReadOnly(result.extension_); }
+        get { return result.extension_; }
       }
       public int ExtensionCount {
         get { return result.ExtensionCount; }
@@ -1117,28 +1047,19 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       public Builder AddExtension(global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto value) {
-        if (result.extension_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty) {
-          result.extension_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
-        }
         result.extension_.Add(value);
         return this;
       }
       public Builder AddExtension(global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto.Builder builderForValue) {
-        if (result.extension_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty) {
-          result.extension_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
-        }
         result.extension_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeExtension(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> values) {
-        if (result.extension_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty) {
-          result.extension_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
-        }
         base.AddRange(values, result.extension_);
         return this;
       }
       public Builder ClearExtension() {
-        result.extension_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty;
+        result.extension_.Clear();
         return this;
       }
       
@@ -1180,7 +1101,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
   }
   
   public sealed partial class DescriptorProto : pb::GeneratedMessage<DescriptorProto, DescriptorProto.Builder> {
-    private static readonly DescriptorProto defaultInstance = new DescriptorProto();
+    private static readonly DescriptorProto defaultInstance = new Builder().BuildPartial();
     public static DescriptorProto DefaultInstance {
       get { return defaultInstance; }
     }
@@ -1204,7 +1125,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     #region Nested types
     public static class Types {
       public sealed partial class ExtensionRange : pb::GeneratedMessage<ExtensionRange, ExtensionRange.Builder> {
-        private static readonly ExtensionRange defaultInstance = new ExtensionRange();
+        private static readonly ExtensionRange defaultInstance = new Builder().BuildPartial();
         public static ExtensionRange DefaultInstance {
           get { return defaultInstance; }
         }
@@ -1466,7 +1387,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     // repeated .google.protobuf.FieldDescriptorProto field = 2;
-    private scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> field_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> field_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
     public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> FieldList {
       get { return field_; } 
     }
@@ -1478,7 +1399,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     // repeated .google.protobuf.FieldDescriptorProto extension = 6;
-    private scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> extension_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> extension_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
     public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> ExtensionList {
       get { return extension_; } 
     }
@@ -1490,7 +1411,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     // repeated .google.protobuf.DescriptorProto nested_type = 3;
-    private scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto> nestedType_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto> nestedType_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>();
     public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto> NestedTypeList {
       get { return nestedType_; } 
     }
@@ -1502,7 +1423,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     // repeated .google.protobuf.EnumDescriptorProto enum_type = 4;
-    private scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto> enumType_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto> enumType_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>();
     public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto> EnumTypeList {
       get { return enumType_; } 
     }
@@ -1514,7 +1435,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     // repeated .google.protobuf.DescriptorProto.ExtensionRange extension_range = 5;
-    private scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange> extensionRange_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange> extensionRange_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange>();
     public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange> ExtensionRangeList {
       get { return extensionRange_; } 
     }
@@ -1672,21 +1593,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }
       
       public override global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto BuildPartial() {
-        if (result.field_ != pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty) {
-          result.field_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.AsReadOnly(result.field_);
-        }
-        if (result.extension_ != pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty) {
-          result.extension_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.AsReadOnly(result.extension_);
-        }
-        if (result.nestedType_ != pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>.Empty) {
-          result.nestedType_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>.AsReadOnly(result.nestedType_);
-        }
-        if (result.enumType_ != pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>.Empty) {
-          result.enumType_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>.AsReadOnly(result.enumType_);
-        }
-        if (result.extensionRange_ != pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange>.Empty) {
-          result.extensionRange_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange>.AsReadOnly(result.extensionRange_);
-        }
+        result.field_.MakeReadOnly();
+        result.extension_.MakeReadOnly();
+        result.nestedType_.MakeReadOnly();
+        result.enumType_.MakeReadOnly();
+        result.extensionRange_.MakeReadOnly();
         global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto returnMe = result;
         result = null;
         return returnMe;
@@ -1707,33 +1618,18 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           Name = other.Name;
         }
         if (other.field_.Count != 0) {
-          if (result.field_.Count == 0) {
-            result.field_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
-          }
           base.AddRange(other.field_, result.field_);
         }
         if (other.extension_.Count != 0) {
-          if (result.extension_.Count == 0) {
-            result.extension_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
-          }
           base.AddRange(other.extension_, result.extension_);
         }
         if (other.nestedType_.Count != 0) {
-          if (result.nestedType_.Count == 0) {
-            result.nestedType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>();
-          }
           base.AddRange(other.nestedType_, result.nestedType_);
         }
         if (other.enumType_.Count != 0) {
-          if (result.enumType_.Count == 0) {
-            result.enumType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>();
-          }
           base.AddRange(other.enumType_, result.enumType_);
         }
         if (other.extensionRange_.Count != 0) {
-          if (result.extensionRange_.Count == 0) {
-            result.extensionRange_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange>();
-          }
           base.AddRange(other.extensionRange_, result.extensionRange_);
         }
         if (other.HasOptions) {
@@ -1833,7 +1729,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       
       // repeated .google.protobuf.FieldDescriptorProto field = 2;
       public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> FieldList {
-        get { return pbc::Lists.AsReadOnly(result.field_); }
+        get { return result.field_; }
       }
       public int FieldCount {
         get { return result.FieldCount; }
@@ -1850,34 +1746,25 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       public Builder AddField(global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto value) {
-        if (result.field_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty) {
-          result.field_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
-        }
         result.field_.Add(value);
         return this;
       }
       public Builder AddField(global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto.Builder builderForValue) {
-        if (result.field_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty) {
-          result.field_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
-        }
         result.field_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeField(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> values) {
-        if (result.field_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty) {
-          result.field_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
-        }
         base.AddRange(values, result.field_);
         return this;
       }
       public Builder ClearField() {
-        result.field_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty;
+        result.field_.Clear();
         return this;
       }
       
       // repeated .google.protobuf.FieldDescriptorProto extension = 6;
       public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> ExtensionList {
-        get { return pbc::Lists.AsReadOnly(result.extension_); }
+        get { return result.extension_; }
       }
       public int ExtensionCount {
         get { return result.ExtensionCount; }
@@ -1894,34 +1781,25 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       public Builder AddExtension(global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto value) {
-        if (result.extension_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty) {
-          result.extension_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
-        }
         result.extension_.Add(value);
         return this;
       }
       public Builder AddExtension(global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto.Builder builderForValue) {
-        if (result.extension_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty) {
-          result.extension_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
-        }
         result.extension_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeExtension(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto> values) {
-        if (result.extension_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty) {
-          result.extension_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>();
-        }
         base.AddRange(values, result.extension_);
         return this;
       }
       public Builder ClearExtension() {
-        result.extension_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.FieldDescriptorProto>.Empty;
+        result.extension_.Clear();
         return this;
       }
       
       // repeated .google.protobuf.DescriptorProto nested_type = 3;
       public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto> NestedTypeList {
-        get { return pbc::Lists.AsReadOnly(result.nestedType_); }
+        get { return result.nestedType_; }
       }
       public int NestedTypeCount {
         get { return result.NestedTypeCount; }
@@ -1938,34 +1816,25 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       public Builder AddNestedType(global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto value) {
-        if (result.nestedType_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>.Empty) {
-          result.nestedType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>();
-        }
         result.nestedType_.Add(value);
         return this;
       }
       public Builder AddNestedType(global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Builder builderForValue) {
-        if (result.nestedType_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>.Empty) {
-          result.nestedType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>();
-        }
         result.nestedType_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeNestedType(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto> values) {
-        if (result.nestedType_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>.Empty) {
-          result.nestedType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>();
-        }
         base.AddRange(values, result.nestedType_);
         return this;
       }
       public Builder ClearNestedType() {
-        result.nestedType_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto>.Empty;
+        result.nestedType_.Clear();
         return this;
       }
       
       // repeated .google.protobuf.EnumDescriptorProto enum_type = 4;
       public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto> EnumTypeList {
-        get { return pbc::Lists.AsReadOnly(result.enumType_); }
+        get { return result.enumType_; }
       }
       public int EnumTypeCount {
         get { return result.EnumTypeCount; }
@@ -1982,34 +1851,25 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       public Builder AddEnumType(global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto value) {
-        if (result.enumType_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>.Empty) {
-          result.enumType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>();
-        }
         result.enumType_.Add(value);
         return this;
       }
       public Builder AddEnumType(global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto.Builder builderForValue) {
-        if (result.enumType_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>.Empty) {
-          result.enumType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>();
-        }
         result.enumType_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeEnumType(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto> values) {
-        if (result.enumType_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>.Empty) {
-          result.enumType_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>();
-        }
         base.AddRange(values, result.enumType_);
         return this;
       }
       public Builder ClearEnumType() {
-        result.enumType_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto>.Empty;
+        result.enumType_.Clear();
         return this;
       }
       
       // repeated .google.protobuf.DescriptorProto.ExtensionRange extension_range = 5;
       public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange> ExtensionRangeList {
-        get { return pbc::Lists.AsReadOnly(result.extensionRange_); }
+        get { return result.extensionRange_; }
       }
       public int ExtensionRangeCount {
         get { return result.ExtensionRangeCount; }
@@ -2026,28 +1886,19 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       public Builder AddExtensionRange(global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange value) {
-        if (result.extensionRange_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange>.Empty) {
-          result.extensionRange_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange>();
-        }
         result.extensionRange_.Add(value);
         return this;
       }
       public Builder AddExtensionRange(global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange.Builder builderForValue) {
-        if (result.extensionRange_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange>.Empty) {
-          result.extensionRange_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange>();
-        }
         result.extensionRange_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeExtensionRange(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange> values) {
-        if (result.extensionRange_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange>.Empty) {
-          result.extensionRange_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange>();
-        }
         base.AddRange(values, result.extensionRange_);
         return this;
       }
       public Builder ClearExtensionRange() {
-        result.extensionRange_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.DescriptorProto.Types.ExtensionRange>.Empty;
+        result.extensionRange_.Clear();
         return this;
       }
       
@@ -2089,7 +1940,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
   }
   
   public sealed partial class FieldDescriptorProto : pb::GeneratedMessage<FieldDescriptorProto, FieldDescriptorProto.Builder> {
-    private static readonly FieldDescriptorProto defaultInstance = new FieldDescriptorProto();
+    private static readonly FieldDescriptorProto defaultInstance = new Builder().BuildPartial();
     public static FieldDescriptorProto DefaultInstance {
       get { return defaultInstance; }
     }
@@ -2651,7 +2502,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
   }
   
   public sealed partial class EnumDescriptorProto : pb::GeneratedMessage<EnumDescriptorProto, EnumDescriptorProto.Builder> {
-    private static readonly EnumDescriptorProto defaultInstance = new EnumDescriptorProto();
+    private static readonly EnumDescriptorProto defaultInstance = new Builder().BuildPartial();
     public static EnumDescriptorProto DefaultInstance {
       get { return defaultInstance; }
     }
@@ -2683,7 +2534,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     // repeated .google.protobuf.EnumValueDescriptorProto value = 2;
-    private scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto> value_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto> value_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto>();
     public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto> ValueList {
       get { return value_; } 
     }
@@ -2817,9 +2668,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }
       
       public override global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto BuildPartial() {
-        if (result.value_ != pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto>.Empty) {
-          result.value_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto>.AsReadOnly(result.value_);
-        }
+        result.value_.MakeReadOnly();
         global::Google.ProtocolBuffers.DescriptorProtos.EnumDescriptorProto returnMe = result;
         result = null;
         return returnMe;
@@ -2840,9 +2689,6 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           Name = other.Name;
         }
         if (other.value_.Count != 0) {
-          if (result.value_.Count == 0) {
-            result.value_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto>();
-          }
           base.AddRange(other.value_, result.value_);
         }
         if (other.HasOptions) {
@@ -2918,7 +2764,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       
       // repeated .google.protobuf.EnumValueDescriptorProto value = 2;
       public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto> ValueList {
-        get { return pbc::Lists.AsReadOnly(result.value_); }
+        get { return result.value_; }
       }
       public int ValueCount {
         get { return result.ValueCount; }
@@ -2935,28 +2781,19 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       public Builder AddValue(global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto value) {
-        if (result.value_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto>.Empty) {
-          result.value_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto>();
-        }
         result.value_.Add(value);
         return this;
       }
       public Builder AddValue(global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto.Builder builderForValue) {
-        if (result.value_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto>.Empty) {
-          result.value_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto>();
-        }
         result.value_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeValue(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto> values) {
-        if (result.value_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto>.Empty) {
-          result.value_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto>();
-        }
         base.AddRange(values, result.value_);
         return this;
       }
       public Builder ClearValue() {
-        result.value_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.EnumValueDescriptorProto>.Empty;
+        result.value_.Clear();
         return this;
       }
       
@@ -2998,7 +2835,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
   }
   
   public sealed partial class EnumValueDescriptorProto : pb::GeneratedMessage<EnumValueDescriptorProto, EnumValueDescriptorProto.Builder> {
-    private static readonly EnumValueDescriptorProto defaultInstance = new EnumValueDescriptorProto();
+    private static readonly EnumValueDescriptorProto defaultInstance = new Builder().BuildPartial();
     public static EnumValueDescriptorProto DefaultInstance {
       get { return defaultInstance; }
     }
@@ -3310,7 +3147,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
   }
   
   public sealed partial class ServiceDescriptorProto : pb::GeneratedMessage<ServiceDescriptorProto, ServiceDescriptorProto.Builder> {
-    private static readonly ServiceDescriptorProto defaultInstance = new ServiceDescriptorProto();
+    private static readonly ServiceDescriptorProto defaultInstance = new Builder().BuildPartial();
     public static ServiceDescriptorProto DefaultInstance {
       get { return defaultInstance; }
     }
@@ -3342,7 +3179,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     // repeated .google.protobuf.MethodDescriptorProto method = 2;
-    private scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto> method_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto>.Empty;
+    private pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto> method_ = new pbc::PopsicleList<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto>();
     public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto> MethodList {
       get { return method_; } 
     }
@@ -3476,9 +3313,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       }
       
       public override global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto BuildPartial() {
-        if (result.method_ != pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto>.Empty) {
-          result.method_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto>.AsReadOnly(result.method_);
-        }
+        result.method_.MakeReadOnly();
         global::Google.ProtocolBuffers.DescriptorProtos.ServiceDescriptorProto returnMe = result;
         result = null;
         return returnMe;
@@ -3499,9 +3334,6 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           Name = other.Name;
         }
         if (other.method_.Count != 0) {
-          if (result.method_.Count == 0) {
-            result.method_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto>();
-          }
           base.AddRange(other.method_, result.method_);
         }
         if (other.HasOptions) {
@@ -3577,7 +3409,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       
       // repeated .google.protobuf.MethodDescriptorProto method = 2;
       public scg::IList<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto> MethodList {
-        get { return pbc::Lists.AsReadOnly(result.method_); }
+        get { return result.method_; }
       }
       public int MethodCount {
         get { return result.MethodCount; }
@@ -3594,28 +3426,19 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       public Builder AddMethod(global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto value) {
-        if (result.method_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto>.Empty) {
-          result.method_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto>();
-        }
         result.method_.Add(value);
         return this;
       }
       public Builder AddMethod(global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto.Builder builderForValue) {
-        if (result.method_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto>.Empty) {
-          result.method_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto>();
-        }
         result.method_.Add(builderForValue.Build());
         return this;
       }
       public Builder AddRangeMethod(scg::IEnumerable<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto> values) {
-        if (result.method_ == pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto>.Empty) {
-          result.method_ = new scg::List<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto>();
-        }
         base.AddRange(values, result.method_);
         return this;
       }
       public Builder ClearMethod() {
-        result.method_ = pbc::Lists<global::Google.ProtocolBuffers.DescriptorProtos.MethodDescriptorProto>.Empty;
+        result.method_.Clear();
         return this;
       }
       
@@ -3657,7 +3480,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
   }
   
   public sealed partial class MethodDescriptorProto : pb::GeneratedMessage<MethodDescriptorProto, MethodDescriptorProto.Builder> {
-    private static readonly MethodDescriptorProto defaultInstance = new MethodDescriptorProto();
+    private static readonly MethodDescriptorProto defaultInstance = new Builder().BuildPartial();
     public static MethodDescriptorProto DefaultInstance {
       get { return defaultInstance; }
     }
@@ -4011,7 +3834,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
   }
   
   public sealed partial class FileOptions : pb::GeneratedMessage<FileOptions, FileOptions.Builder> {
-    private static readonly FileOptions defaultInstance = new FileOptions();
+    private static readonly FileOptions defaultInstance = new Builder().BuildPartial();
     public static FileOptions DefaultInstance {
       get { return defaultInstance; }
     }
@@ -4568,7 +4391,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
   }
   
   public sealed partial class MessageOptions : pb::GeneratedMessage<MessageOptions, MessageOptions.Builder> {
-    private static readonly MessageOptions defaultInstance = new MessageOptions();
+    private static readonly MessageOptions defaultInstance = new Builder().BuildPartial();
     public static MessageOptions DefaultInstance {
       get { return defaultInstance; }
     }
@@ -4775,7 +4598,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
   }
   
   public sealed partial class FieldOptions : pb::GeneratedMessage<FieldOptions, FieldOptions.Builder> {
-    private static readonly FieldOptions defaultInstance = new FieldOptions();
+    private static readonly FieldOptions defaultInstance = new Builder().BuildPartial();
     public static FieldOptions DefaultInstance {
       get { return defaultInstance; }
     }
@@ -5038,7 +4861,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
   }
   
   public sealed partial class EnumOptions : pb::GeneratedMessage<EnumOptions, EnumOptions.Builder> {
-    private static readonly EnumOptions defaultInstance = new EnumOptions();
+    private static readonly EnumOptions defaultInstance = new Builder().BuildPartial();
     public static EnumOptions DefaultInstance {
       get { return defaultInstance; }
     }
@@ -5203,7 +5026,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
   }
   
   public sealed partial class EnumValueOptions : pb::GeneratedMessage<EnumValueOptions, EnumValueOptions.Builder> {
-    private static readonly EnumValueOptions defaultInstance = new EnumValueOptions();
+    private static readonly EnumValueOptions defaultInstance = new Builder().BuildPartial();
     public static EnumValueOptions DefaultInstance {
       get { return defaultInstance; }
     }
@@ -5368,7 +5191,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
   }
   
   public sealed partial class ServiceOptions : pb::GeneratedMessage<ServiceOptions, ServiceOptions.Builder> {
-    private static readonly ServiceOptions defaultInstance = new ServiceOptions();
+    private static readonly ServiceOptions defaultInstance = new Builder().BuildPartial();
     public static ServiceOptions DefaultInstance {
       get { return defaultInstance; }
     }
@@ -5533,7 +5356,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
   }
   
   public sealed partial class MethodOptions : pb::GeneratedMessage<MethodOptions, MethodOptions.Builder> {
-    private static readonly MethodOptions defaultInstance = new MethodOptions();
+    private static readonly MethodOptions defaultInstance = new Builder().BuildPartial();
     public static MethodOptions DefaultInstance {
       get { return defaultInstance; }
     }
diff --git a/csharp/ProtocolBuffers/FieldAccess/Delegates.cs b/csharp/ProtocolBuffers/FieldAccess/Delegates.cs
deleted file mode 100644
index 972961c6..00000000
--- a/csharp/ProtocolBuffers/FieldAccess/Delegates.cs
+++ /dev/null
@@ -1,26 +0,0 @@
-// 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);
-}
diff --git a/csharp/ProtocolBuffers/MessageStreamIterator.cs b/csharp/ProtocolBuffers/MessageStreamIterator.cs
index 4944e5ce..61dbf840 100644
--- a/csharp/ProtocolBuffers/MessageStreamIterator.cs
+++ b/csharp/ProtocolBuffers/MessageStreamIterator.cs
@@ -8,25 +8,67 @@ using System.Reflection;
 namespace Google.ProtocolBuffers {
 
   /// <summary>
-  /// Helper class to create MessageStreamIterators without explicitly specifying
-  /// the builder type. The concrete builder type is determined by reflection, based
-  /// on the message type. The reflection step looks for a <c>CreateBuilder</c> method
-  /// in the message type which is public and static, and uses the return type of that
-  /// method as the builder type. This will work for all generated messages, whether
-  /// optimised for size or speed. It won't work for dynamic messages.
-  /// 
-  /// TODO(jonskeet): This also won't work for non-public protos :(
-  /// Pass in delegate to create a builder?
+  /// Iterates over data created using a <see cref="MessageStreamWriter{T}" />.
+  /// Unlike MessageStreamWriter, this class is not usually constructed directly with
+  /// a stream; instead it is provided with a way of opening a stream when iteration
+  /// is started. The stream is closed when the iteration is completed or the enumerator
+  /// is disposed. (This occurs naturally when using <c>foreach</c>.)
   /// </summary>
-  public static class MessageStreamIterator {
+  public class MessageStreamIterator<TMessage> : IEnumerable<TMessage>
+      where TMessage : IMessage<TMessage> {
+
+    private readonly StreamProvider streamProvider;
+    private readonly ExtensionRegistry extensionRegistry;
+
+    /// <summary>
+    /// Delegate created via reflection trickery (once per type) to create a builder
+    /// and read a message from a CodedInputStream with it. Note that unlike in Java,
+    /// there's one static field per constructed type.
+    /// </summary>
+    private static readonly Func<CodedInputStream, ExtensionRegistry, TMessage> messageReader = BuildMessageReader();
+
+    /// <summary>
+    /// Any exception (within reason) thrown within messageReader is caught and rethrown in the constructor.
+    /// This makes life a lot simpler for the caller.
+    /// </summary>
+    private static Exception typeInitializationException;
+
+    /// <summary>
+    /// Creates the delegate later used to read messages. This is only called once per type, but to
+    /// avoid exceptions occurring at confusing times, if this fails it will set typeInitializationException
+    /// to the appropriate error and return null.
+    /// </summary>
+    private static Func<CodedInputStream, ExtensionRegistry, TMessage> BuildMessageReader() {
+      try {
+        Type builderType = FindBuilderType();
+
+        // Yes, it's redundant to find this again, but it's only the once...
+        MethodInfo createBuilderMethod = typeof(TMessage).GetMethod("CreateBuilder", Type.EmptyTypes);
+        Delegate builderBuilder = Delegate.CreateDelegate(
+            typeof(Func<>).MakeGenericType(builderType), null, createBuilderMethod);
 
-    public static IEnumerable<TMessage> FromFile<TMessage>(string file) 
-        where TMessage : IMessage<TMessage> {
-      return FromStreamProvider<TMessage>(() => File.OpenRead(file));
+        MethodInfo buildMethod = typeof(MessageStreamIterator<TMessage>)
+            .GetMethod("BuildImpl", BindingFlags.Static | BindingFlags.NonPublic)
+            .MakeGenericMethod(typeof(TMessage), builderType);
+
+        return (Func<CodedInputStream, ExtensionRegistry, TMessage>)Delegate.CreateDelegate(
+          typeof(Func<CodedInputStream, ExtensionRegistry, TMessage>), builderBuilder, buildMethod);
+      } catch (ArgumentException e) {
+        typeInitializationException = e;
+      } catch (InvalidOperationException e) {
+        typeInitializationException = e;
+      } catch (InvalidCastException e) {
+        // Can't see why this would happen, but best to know about it.
+        typeInitializationException = e;
+      }
+      return null;
     }
 
-    public static IEnumerable<TMessage> FromStreamProvider<TMessage>(StreamProvider streamProvider)
-        where TMessage : IMessage<TMessage> {
+    /// <summary>
+    /// Works out the builder type for TMessage, or throws an ArgumentException to explain why it can't.
+    /// This will check 
+    /// </summary>
+    private static Type FindBuilderType() {
       MethodInfo createBuilderMethod = typeof(TMessage).GetMethod("CreateBuilder", Type.EmptyTypes);
       if (createBuilderMethod == null) {
         throw new ArgumentException("Message type " + typeof(TMessage).FullName + " has no CreateBuilder method.");
@@ -35,68 +77,57 @@ namespace Google.ProtocolBuffers {
         throw new ArgumentException("CreateBuilder method in " + typeof(TMessage).FullName + " has void return type");
       }
       Type builderType = createBuilderMethod.ReturnType;
-      if (builderType.GetConstructor(Type.EmptyTypes) == null) {
-        throw new ArgumentException("Builder type " + builderType.FullName + " has no public parameterless constructor.");
-      }
       Type messageInterface = typeof(IMessage<,>).MakeGenericType(typeof(TMessage), builderType);
       Type builderInterface = typeof(IBuilder<,>).MakeGenericType(typeof(TMessage), builderType);
-      if (Array.IndexOf(typeof (TMessage).GetInterfaces(), messageInterface) == -1) {
+      if (Array.IndexOf(typeof(TMessage).GetInterfaces(), messageInterface) == -1) {
         throw new ArgumentException("Message type " + typeof(TMessage) + " doesn't implement " + messageInterface.FullName);
       }
       if (Array.IndexOf(builderType.GetInterfaces(), builderInterface) == -1) {
         throw new ArgumentException("Builder type " + typeof(TMessage) + " doesn't implement " + builderInterface.FullName);
       }
-      Type iteratorType = typeof(MessageStreamIterator<,>).MakeGenericType(typeof(TMessage), builderType);
-      MethodInfo factoryMethod = iteratorType.GetMethod("FromStreamProvider", new Type[] { typeof(StreamProvider) });
-      return (IEnumerable<TMessage>) factoryMethod.Invoke(null, new object[] { streamProvider });
+      return builderType;
     }
-  }
 
-  /// <summary>
-  /// Iterates over data created using a <see cref="MessageStreamWriter{T}" />.
-  /// Unlike MessageStreamWriter, this class is not usually constructed directly with
-  /// a stream; instead it is provided with a way of opening a stream when iteration
-  /// is started. The stream is closed when the iteration is completed or the enumerator
-  /// is disposed. (This occurs naturally when using <c>foreach</c>.)
-  /// This type is generic in both the message type and the builder type; if only the
-  /// iteration is required (i.e. just <see cref="IEnumerable{T}" />) then the static
-  /// generic methods in the nongeneric class are more appropriate.
-  /// </summary>
-  public sealed class MessageStreamIterator<TMessage, TBuilder> : IEnumerable<TMessage> 
-      where TMessage : IMessage<TMessage, TBuilder>
-      where TBuilder : IBuilder<TMessage, TBuilder>, new() {
-
-    private readonly StreamProvider streamProvider;
-    private readonly ExtensionRegistry extensionRegistry;
+    /// <summary>
+    /// Method we'll use to build messageReader, with the first parameter fixed to TMessage.CreateBuilder. Note that we
+    /// have to introduce another type parameter (TMessage2) as we can't constrain TMessage for just a single method
+    /// (and we can't do it at the type level because we don't know TBuilder). However, by constraining TMessage2
+    /// to not only implement IMessage appropriately but also to derive from TMessage2, we can avoid doing a cast
+    /// for every message; the implicit reference conversion will be fine. In practice, TMessage2 and TMessage will
+    /// be the same type when we construct the generic method by reflection.
+    /// </summary>
+    private static TMessage BuildImpl<TMessage2, TBuilder>(Func<TBuilder> builderBuilder, CodedInputStream input, ExtensionRegistry registry) 
+        where TBuilder : IBuilder<TMessage2, TBuilder>
+        where TMessage2 : TMessage, IMessage<TMessage2, TBuilder> {
+      TBuilder builder = builderBuilder();
+      input.ReadMessage(builder, registry);
+      return builder.Build();
+    }
+    
     private static readonly uint ExpectedTag = WireFormat.MakeTag(1, WireFormat.WireType.LengthDelimited);
 
     private MessageStreamIterator(StreamProvider streamProvider, ExtensionRegistry extensionRegistry) {
+      if (messageReader == null) {
+        throw typeInitializationException;
+      }
       this.streamProvider = streamProvider;
       this.extensionRegistry = extensionRegistry;
     }
 
     /// <summary>
-    /// Creates an instance which opens the specified file when it begins
-    /// iterating. No extension registry is used when reading messages.
+    /// Creates a new instance which uses the same stream provider as this one,
+    /// but the specified extension registry.
     /// </summary>
-    public static MessageStreamIterator<TMessage, TBuilder> FromFile(string file) {
-      return new MessageStreamIterator<TMessage, TBuilder>(() => File.OpenRead(file), ExtensionRegistry.Empty);
+    public MessageStreamIterator<TMessage> WithExtensionRegistry(ExtensionRegistry newRegistry) {
+      return new MessageStreamIterator<TMessage>(streamProvider, newRegistry);
     }
 
-    /// <summary>
-    /// Creates an instance which calls the given delegate when it begins
-    /// iterating. No extension registry is used when reading messages.
-    /// </summary>
-    public static MessageStreamIterator<TMessage, TBuilder> FromStreamProvider(StreamProvider streamProvider) {
-      return new MessageStreamIterator<TMessage, TBuilder>(streamProvider, ExtensionRegistry.Empty);
+    public static MessageStreamIterator<TMessage> FromFile(string file) {
+      return new MessageStreamIterator<TMessage>(() => File.OpenRead(file), ExtensionRegistry.Empty);
     }
 
-    /// <summary>
-    /// Creates a new instance which uses the same stream provider as this one,
-    /// but the specified extension registry.
-    /// </summary>
-    public MessageStreamIterator<TMessage, TBuilder> WithExtensionRegistry(ExtensionRegistry newRegistry) {
-      return new MessageStreamIterator<TMessage, TBuilder>(streamProvider, newRegistry);
+    public static MessageStreamIterator<TMessage> FromStreamProvider(StreamProvider streamProvider) {
+      return new MessageStreamIterator<TMessage>(streamProvider, ExtensionRegistry.Empty);
     }
 
     public IEnumerator<TMessage> GetEnumerator() {
@@ -107,16 +138,11 @@ namespace Google.ProtocolBuffers {
           if (tag != ExpectedTag) {
             throw InvalidProtocolBufferException.InvalidMessageStreamTag();
           }
-          TBuilder builder = new TBuilder();
-          input.ReadMessage(builder, extensionRegistry);
-          yield return builder.Build();
+          yield return messageReader(input, extensionRegistry);
         }
       }
     }
 
-    /// <summary>
-    /// Explicit implementation of nongeneric IEnumerable interface.
-    /// </summary>
     IEnumerator IEnumerable.GetEnumerator() {
       return GetEnumerator();
     }
diff --git a/csharp/ProtocolBuffers/ProtocolBuffers.csproj b/csharp/ProtocolBuffers/ProtocolBuffers.csproj
index 25f7cdbb..70a4691d 100644
--- a/csharp/ProtocolBuffers/ProtocolBuffers.csproj
+++ b/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" />