base/auto_reset.h

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_AUTO_RESET_H_
   6 #define BASE_AUTO_RESET_H_
   7
   8 #include "base/basictypes.h"
   9
  10 // base::AutoReset<> is useful for setting a variable to a new value only within
  11 // a particular scope. An base::AutoReset<> object resets a variable to its
  12 // original value upon destruction, making it an alternative to writing
  13 // "var = false;" or "var = old_val;" at all of a block's exit points.
  14 //
  15 // This should be obvious, but note that an base::AutoReset<> instance should
  16 // have a shorter lifetime than its scoped_variable, to prevent invalid memory
  17 // writes when the base::AutoReset<> object is destroyed.
  18
  19 namespace base {
  20
  21 template<typename T>
  22 class AutoReset {
  23  public:
  24   AutoReset(T* scoped_variable, T new_value)
  25       : scoped_variable_(scoped_variable),
  26         original_value_(*scoped_variable) {
  27     *scoped_variable_ = new_value;
  28   }
  29
  30   ~AutoReset() { *scoped_variable_ = original_value_; }
  31
  32  private:
  33   T* scoped_variable_;
  34   T original_value_;
  35
  36   DISALLOW_COPY_AND_ASSIGN(AutoReset);
  37 };
  38
  39 }  // namespace base
  40
  41 #endif  // BASE_AUTO_RESET_H_