1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
3 /* This Source Code Form is subject to the terms of the Mozilla Public
4  * License, v. 2.0. If a copy of the MPL was not distributed with this
5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
6 
7 /* functions for restoring saved values at the end of a C++ scope */
8 
9 #ifndef mozilla_AutoRestore_h_
10 #define mozilla_AutoRestore_h_
11 
12 #include "mozilla/Attributes.h"  // MOZ_STACK_CLASS
13 #include "mozilla/GuardObjects.h"
14 
15 namespace mozilla {
16 
17 /**
18  * Save the current value of a variable and restore it when the object
19  * goes out of scope.  For example:
20  *   {
21  *     AutoRestore<bool> savePainting(mIsPainting);
22  *     mIsPainting = true;
23  *
24  *     // ... your code here ...
25  *
26  *     // mIsPainting is reset to its old value at the end of this block
27  *   }
28  */
29 template <class T>
30 class MOZ_RAII AutoRestore {
31  private:
32   T& mLocation;
33   T mValue;
34   MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
35  public:
AutoRestore(T & aValue MOZ_GUARD_OBJECT_NOTIFIER_PARAM)36   explicit AutoRestore(T& aValue MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
37       : mLocation(aValue), mValue(aValue) {
38     MOZ_GUARD_OBJECT_NOTIFIER_INIT;
39   }
~AutoRestore()40   ~AutoRestore() { mLocation = mValue; }
SavedValue()41   T SavedValue() const { return mValue; }
42 };
43 
44 }  // namespace mozilla
45 
46 #endif /* !defined(mozilla_AutoRestore_h_) */
47