Add rtc::Optional::emplace

webrtc/base/optional.h

 /*
  *  Copyright 2015 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 175 matching lines @@
 
   // Destroy any contained value. Has no effect if we have no value.
   void reset() {
     if (!has_value_)
       return;
     value_.~T();
     has_value_ = false;
     PoisonValue();
   }
 
+  template <class... Args>
+  void emplace(Args&&... args) {
+    if (has_value_)
+      value_.~T();
+    else
+      UnpoisonValue();
+    new (&value_) T(std::forward<Args>(args)...);
+    has_value_ = true;
+  }
+
   // Conversion to bool to test if we have a value.
   explicit operator bool() const { return has_value_; }
 
   // Dereferencing. Only allowed if we have a value.
   const T* operator->() const {
     RTC_DCHECK(has_value_);
     return &value_;
   }
   T* operator->() {
     RTC_DCHECK(has_value_);
@@ skipping 52 matching lines @@
     // construct it, and the Optional destructor won't automatically destroy
     // it. Basically, this just allocates a properly sized and aligned block of
     // memory in which we can manually put a T with placement new.
     T value_;
   };
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_OPTIONAL_H_