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      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
     69