third_party/WebKit/Source/wtf/TemporaryChange.h

   1 /*
   2  * Copyright (C) 2011 Google Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  *
   8  * 1.  Redistributions of source code must retain the above copyright
   9  *     notice, this list of conditions and the following disclaimer.
  10  * 2.  Redistributions in binary form must reproduce the above copyright
  11  *     notice, this list of conditions and the following disclaimer in the
  12  *     documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
  15  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  16  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  17  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
  18  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  19  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  20  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  21  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  23  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #ifndef TemporaryChange_h
  27 #define TemporaryChange_h
  28
  29 #include "wtf/Noncopyable.h"
  30
  31 namespace WTF {
  32
  33 // TemporaryChange<> is useful for setting a variable to a new value only within a
  34 // particular scope. An TemporaryChange<> object changes a variable to its original
  35 // value upon destruction, making it an alternative to writing "var = false;"
  36 // or "var = oldVal;" at all of a block's exit points.
  37 //
  38 // This should be obvious, but note that an TemporaryChange<> instance should have a
  39 // shorter lifetime than its scopedVariable, to prevent invalid memory writes
  40 // when the TemporaryChange<> object is destroyed.
  41
  42 template<typename T>
  43 class TemporaryChange {
  44     WTF_MAKE_NONCOPYABLE(TemporaryChange);
  45 public:
  46     TemporaryChange(T& scopedVariable, T newValue)
  47         : m_scopedVariable(scopedVariable)
  48         , m_originalValue(scopedVariable)
  49     {
  50         m_scopedVariable = newValue;
  51     }
  52
  53     ~TemporaryChange()
  54     {
  55         m_scopedVariable = m_originalValue;
  56     }
  57
  58
  59 private:
  60     T& m_scopedVariable;
  61     T m_originalValue;
  62 };
  63
  64 }
  65
  66 using WTF::TemporaryChange;
  67
  68 #endif