Added an empty member to the union of rtc::Optional, so that it is always initializable.

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 41 matching lines @@
 //   Optional<double> when parsing a single number as in the example above
 //   might make sense, but any larger parse job is probably going to need to
 //   tell the caller what the problem was, not just that there was one.
 //
 // TODO(kwiberg): Get rid of this class when the standard library has
 // std::optional (and we're allowed to use it).
 template <typename T>
 class Optional final {
  public:
   // Construct an empty Optional.
-  Optional() : has_value_(false) {}
+  Optional() : has_value_(false), empty_('\0') {}
 
   // Construct an Optional that contains a value.
   explicit Optional(const T& value) : has_value_(true) {
     new (&value_) T(value);
   }
   explicit Optional(T&& value) : has_value_(true) {
     new (&value_) T(std::move(value));
   }
 
   // Copy constructor: copies the value from m if it has one.
@@ skipping 109 matching lines @@
                                           : m1.has_value_ == m2.has_value_;
   }
   friend bool operator!=(const Optional& m1, const Optional& m2) {
     return m1.has_value_ && m2.has_value_ ? m1.value_ != m2.value_
                                           : m1.has_value_ != m2.has_value_;
   }
 
  private:
   bool has_value_;  // True iff value_ contains a live value.
   union {
+    // empty_ exists only to make it possible to initialize the union, even when
+    // it doesn't contain any data. If the union goes uninitialized, it may
+    // trigger compiler warnings.
+    char empty_;
     // By placing value_ in a union, we get to manage its construction and
     // destruction manually: the Optional constructors won't automatically
     // 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_