Add ability to return moved value from FunctorMessageHandler, Optional.

webrtc/base/messagehandler.h

 /*
  *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 27 matching lines @@
 template <class ReturnT, class FunctorT>
 class FunctorMessageHandler : public MessageHandler {
  public:
   explicit FunctorMessageHandler(const FunctorT& functor)
       : functor_(functor) {}
   virtual void OnMessage(Message* msg) {
     result_ = functor_();
   }
   const ReturnT& result() const { return result_; }
 
+  // Returns moved result. Should not call result() or ConsumeResult() again
+  // after this.

[pthatcher1, 2017/02/10 18:18:01]

What happens if you do?

[Taylor Brandstetter, 2017/02/10 19:29:42]

Undefined behavior.

+  ReturnT ConsumeResult() { return std::move(result_); }

[tommi, 2017/02/10 19:38:55]

MoveResult() ?

[Taylor Brandstetter, 2017/02/11 01:03:30]

Done.

+
  private:
   FunctorT functor_;
   ReturnT result_;
 };
 
-// Specialization for std::unique_ptr<ReturnT>.
-template <class ReturnT, class FunctorT>
-class FunctorMessageHandler<class std::unique_ptr<ReturnT>, FunctorT>
-    : public MessageHandler {
- public:
-  explicit FunctorMessageHandler(const FunctorT& functor) : functor_(functor) {}
-  virtual void OnMessage(Message* msg) { result_ = std::move(functor_()); }
-  std::unique_ptr<ReturnT> result() { return std::move(result_); }
-
- private:
-  FunctorT functor_;
-  std::unique_ptr<ReturnT> result_;
-};
-
 // Specialization for ReturnT of void.
 template <class FunctorT>
 class FunctorMessageHandler<void, FunctorT> : public MessageHandler {
  public:
   explicit FunctorMessageHandler(const FunctorT& functor)
       : functor_(functor) {}
   virtual void OnMessage(Message* msg) {
     functor_();
   }
   void result() const {}
+  void ConsumeResult() {}
 
  private:
   FunctorT functor_;
 };
 
 } // namespace rtc
 
 #endif // WEBRTC_BASE_MESSAGEHANDLER_H_