Add ability to return moved value from FunctorMessageHandler, Optional.

webrtc/base/messagehandler.h

Index: webrtc/base/messagehandler.h
diff --git a/webrtc/base/messagehandler.h b/webrtc/base/messagehandler.h
index 6a3c2ef7402bdf9203ef350dcff740f806d1210d..66c6bdfb5926aa80d13d7284b91f383aa317b077 100644
--- a/webrtc/base/messagehandler.h
+++ b/webrtc/base/messagehandler.h
@@ -45,23 +45,13 @@ class FunctorMessageHandler : public MessageHandler {
   }
   const ReturnT& result() const { return result_; }
 
- 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_); }
+  // 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_;
-  std::unique_ptr<ReturnT> result_;
+  ReturnT result_;
 };
 
 // Specialization for ReturnT of void.
@@ -74,6 +64,7 @@ class FunctorMessageHandler<void, FunctorT> : public MessageHandler {
     functor_();
   }
   void result() const {}
+  void ConsumeResult() {}
 
  private:
   FunctorT functor_;