1/*
2 * Copyright (C) 2011 Google Inc. All rights reserved.
3 * Copyright (C) 2016 Apple Inc. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
16 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
17 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
18 * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
19 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
20 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
21 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
22 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27#pragma once
28
29#include <wtf/Noncopyable.h>
30#include <wtf/StdLibExtras.h>
31
32namespace WTF {
33
34// SetForScope<> is useful for setting a variable to a new value only within a
35// particular scope. An SetForScope<> object changes a variable to its original
36// value upon destruction, making it an alternative to writing "var = false;"
37// or "var = oldVal;" at all of a block's exit points.
38//
39// This should be obvious, but note that an SetForScope<> instance should have a
40// shorter lifetime than its scopedVariable, to prevent invalid memory writes
41// when the SetForScope<> object is destroyed.
42
43template<typename T>
44class SetForScope {
45 WTF_MAKE_NONCOPYABLE(SetForScope);
46public:
47 SetForScope(T& scopedVariable)
48 : m_scopedVariable(scopedVariable)
49 , m_originalValue(scopedVariable)
50 {
51 }
52 template<typename U>
53 SetForScope(T& scopedVariable, U&& newValue)
54 : SetForScope(scopedVariable)
55 {
56 m_scopedVariable = std::forward<U>(newValue);
57 }
58
59 ~SetForScope()
60 {
61 m_scopedVariable = WTFMove(m_originalValue);
62 }
63
64private:
65 T& m_scopedVariable;
66 T m_originalValue;
67};
68
69}
70
71using WTF::SetForScope;
72