| // 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 BASE_AUTO_RESET_H_ | 
 | #define 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  // BASE_AUTO_RESET_H_ |