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: TemporaryChange(T & scopedVariable,T newValue)46 TemporaryChange(T& scopedVariable, T newValue) 47 : m_scopedVariable(scopedVariable) 48 , m_originalValue(scopedVariable) 49 { 50 m_scopedVariable = newValue; 51 } 52 ~TemporaryChange()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