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
31namespace 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
42template<typename T>
43class TemporaryChange {
44    WTF_MAKE_NONCOPYABLE(TemporaryChange);
45public:
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
59private:
60    T& m_scopedVariable;
61    T m_originalValue;
62};
63
64}
65
66using WTF::TemporaryChange;
67
68#endif
69