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-/*
- * 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. Note: These are non-explicit, so
- // that a T will implicitly convert to Maybe<T>.
- Maybe(const T& val) : value_(val), has_value_(true) {}
- 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. Note that we allow assignment from either Maybe<T> or plain T.
- // 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;
- }
- Maybe& operator=(const T& val) {
- value_ = val;
- has_value_ = true;
- return *this;
- }
- Maybe& operator=(T&& val) {
- value_ = static_cast<T&&>(val);
- has_value_ = true;
- 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_