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diff --git a/src/google/protobuf/dynamic_message.h b/src/google/protobuf/dynamic_message.h
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+// 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.
+
+// Author: kenton@google.com (Kenton Varda)
+//  Based on original Protocol Buffers design by
+//  Sanjay Ghemawat, Jeff Dean, and others.
+//
+// Defines an implementation of Message which can emulate types which are not
+// known at compile-time.
+
+#ifndef GOOGLE_PROTOBUF_DYNAMIC_MESSAGE_H__
+#define GOOGLE_PROTOBUF_DYNAMIC_MESSAGE_H__
+
+#include <google/protobuf/message.h>
+#include <google/protobuf/stubs/common.h>
+
+namespace google {
+namespace protobuf {
+
+// Defined in other files.
+class Descriptor;        // descriptor.h
+class DescriptorPool;    // descriptor.h
+
+// Constructs implementations of Message which can emulate types which are not
+// known at compile-time.
+//
+// Sometimes you want to be able to manipulate protocol types that you don't
+// know about at compile time.  It would be nice to be able to construct
+// a Message object which implements the message type given by any arbitrary
+// Descriptor.  DynamicMessage provides this.
+//
+// As it turns out, a DynamicMessage needs to construct extra
+// information about its type in order to operate.  Most of this information
+// can be shared between all DynamicMessages of the same type.  But, caching
+// this information in some sort of global map would be a bad idea, since
+// the cached information for a particular descriptor could outlive the
+// descriptor itself.  To avoid this problem, DynamicMessageFactory
+// encapsulates this "cache".  All DynamicMessages of the same type created
+// from the same factory will share the same support data.  Any Descriptors
+// used with a particular factory must outlive the factory.
+class LIBPROTOBUF_EXPORT DynamicMessageFactory : public MessageFactory {
+ public:
+  // Construct a DynamicMessageFactory that will search for extensions in
+  // the DescriptorPool in which the exendee is defined.
+  DynamicMessageFactory();
+
+  // Construct a DynamicMessageFactory that will search for extensions in
+  // the given DescriptorPool.
+  DynamicMessageFactory(const DescriptorPool* pool);
+  ~DynamicMessageFactory();
+
+  // implements MessageFactory ---------------------------------------
+
+  // Given a Descriptor, constructs the default (prototype) Message of that
+  // type.  You can then call that message's New() method to construct a
+  // mutable message of that type.
+  //
+  // Calling this method twice with the same Descriptor returns the same
+  // object.  The returned object remains property of the factory and will
+  // be destroyed when the factory is destroyed.  Also, any objects created
+  // by calling the prototype's New() method share some data with the
+  // prototype, so these must be destoyed before the DynamicMessageFactory
+  // is destroyed.
+  //
+  // The given descriptor must outlive the returned message, and hence must
+  // outlive the DynamicMessageFactory.
+  //
+  // Note that while GetPrototype() is idempotent, it is not const.  This
+  // implies that it is not thread-safe to call GetPrototype() on the same
+  // DynamicMessageFactory in two different threads simultaneously.  However,
+  // the returned objects are just as thread-safe as any other Message.
+  const Message* GetPrototype(const Descriptor* type);
+
+ private:
+  const DescriptorPool* pool_;
+
+  // This struct just contains a hash_map.  We can't #include <google/protobuf/stubs/hash.h> from
+  // this header due to hacks needed for hash_map portability in the open source
+  // release.  Namely, stubs/hash.h, which defines hash_map portably, is not a
+  // public header (for good reason), but dynamic_message.h is, and public
+  // headers may only #include other public headers.
+  struct PrototypeMap;
+  scoped_ptr<PrototypeMap> prototypes_;
+
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(DynamicMessageFactory);
+};
+
+}  // namespace protobuf
+
+}  // namespace google
+#endif  // GOOGLE_PROTOBUF_DYNAMIC_MESSAGE_H__
+