Rename Maybe to Optional

webrtc/base/maybe.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.
- */
-
-#ifndef WEBRTC_BASE_MAYBE_H_
-#define WEBRTC_BASE_MAYBE_H_
-
-#include <algorithm>
-#include <utility>
-
-#include "webrtc/base/checks.h"
-
-namespace rtc {
-
-// Simple std::experimental::optional-wannabe. It either contains a T or not.
-// In order to keep the implementation simple and portable, this implementation
-// actually contains a (default-constructed) T even when it supposedly doesn't
-// contain a value; use e.g. rtc::scoped_ptr<T> instead if that's too
-// expensive.
-//
-// A moved-from Maybe<T> may only be destroyed, and assigned to if T allows
-// being assigned to after having been moved from. Specifically, you may not
-// assume that it just doesn't contain a value anymore.
-//
-// 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 Maybe final {
- public:
-  // Construct an empty Maybe.
-  Maybe() : has_value_(false) {}
-
-  // Construct a Maybe that contains a value.
-  explicit Maybe(const T& val) : value_(val), has_value_(true) {}
-  explicit Maybe(T&& val) : value_(static_cast<T&&>(val)), has_value_(true) {}
-
-  // Copy and move constructors.
-  // TODO(kwiberg): =default the move constructor when MSVC supports it.
-  Maybe(const Maybe&) = default;
-  Maybe(Maybe&& m)
-      : value_(static_cast<T&&>(m.value_)), has_value_(m.has_value_) {}
-
-  // Assignment.
-  // TODO(kwiberg): =default the move assignment op when MSVC supports it.
-  Maybe& operator=(const Maybe&) = default;
-  Maybe& operator=(Maybe&& m) {
-    value_ = static_cast<T&&>(m.value_);
-    has_value_ = m.has_value_;
-    return *this;
-  }
-
-  friend void swap(Maybe& m1, Maybe& m2) {
-    using std::swap;
-    swap(m1.value_, m2.value_);
-    swap(m1.has_value_, m2.has_value_);
-  }
-
-  // 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_);
-    return &value_;
-  }
-  const T& operator*() const {
-    RTC_DCHECK(has_value_);
-    return value_;
-  }
-  T& operator*() {
-    RTC_DCHECK(has_value_);
-    return value_;
-  }
-
-  // Dereference with a default value in case we don't have a value.
-  const T& value_or(const T& default_val) const {
-    return has_value_ ? value_ : default_val;
-  }
-
-  // Equality tests. Two Maybes are equal if they contain equivalent values, or
-  // if they're both empty.
-  friend bool operator==(const Maybe& m1, const Maybe& m2) {
-    return m1.has_value_ && m2.has_value_ ? m1.value_ == m2.value_
-                                          : m1.has_value_ == m2.has_value_;
-  }
-  friend bool operator!=(const Maybe& m1, const Maybe& m2) {
-    return m1.has_value_ && m2.has_value_ ? m1.value_ != m2.value_
-                                          : m1.has_value_ != m2.has_value_;
-  }
-
- private:
-  // Invariant: Unless *this has been moved from, value_ is default-initialized
-  // (or copied or moved from a default-initialized T) if !has_value_.
-  T value_;
-  bool has_value_;
-};
-
-}  // namespace rtc
-
-#endif  // WEBRTC_BASE_MAYBE_H_