auto_reset.h

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// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#ifndef ACCESSIBILITY_BASE_AUTO_RESET_H_
#define ACCESSIBILITY_BASE_AUTO_RESET_H_
 
#include <utility>
 
// base::AutoReset<> is useful for setting a variable to a new value only within
// a particular scope. An base::AutoReset<> object resets a variable to its
// original value upon destruction, making it an alternative to writing
// "var = false;" or "var = old_val;" at all of a block's exit points.
//
// This should be obvious, but note that an base::AutoReset<> instance should
// have a shorter lifetime than its scoped_variable, to prevent invalid memory
// writes when the base::AutoReset<> object is destroyed.
 
namespace base {
 
template <typename T>
class AutoReset {
 public:
  template <typename U>
  AutoReset(T* scoped_variable, U&& new_value)
      : scoped_variable_(scoped_variable),
        original_value_(
            std::exchange(*scoped_variable_, std::forward<U>(new_value))) {}
 
  AutoReset(AutoReset&& other)
      : scoped_variable_(std::exchange(other.scoped_variable_, nullptr)),
        original_value_(std::move(other.original_value_)) {}
 
  AutoReset& operator=(AutoReset&& rhs) {
    scoped_variable_ = std::exchange(rhs.scoped_variable_, nullptr);
    original_value_ = std::move(rhs.original_value_);
    return *this;
  }
 
  ~AutoReset() {
    if (scoped_variable_)
      *scoped_variable_ = std::move(original_value_);
  }
 
 private:
  T* scoped_variable_;
  T original_value_;
};
 
}  // namespace base
 
#endif  // ACCESSIBILITY_BASE_AUTO_RESET_H_