Add QScopedValueRollback tools class.

This template allows a value to be automatically rolled back to a previous
state when the class goes out of scope. This can be used to maintain a
valid state when an exception is thrown.

Reviewed-by: mread
Reviewed-by: joao

1 files changed, 84 insertions, 0 deletions

diff --git a/src/corelib/tools/qscopedvaluerollback.cpp b/src/corelib/tools/qscopedvaluerollback.cpp
new file mode 100644
index 0000000..8933efc
--- /dev/null
+++ b/src/corelib/tools/qscopedvaluerollback.cpp
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+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** No Commercial Usage
+** This file contains pre-release code and may not be distributed.
+** You may use this file in accordance with the terms and conditions
+** contained in the Technology Preview License Agreement accompanying
+** this package.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
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+** In addition, as a special exception, Nokia gives you certain additional
+** rights.  These rights are described in the Nokia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** If you have questions regarding the use of this file, please contact
+** Nokia at qt-info@nokia.com.
+**
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+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qscopedvaluerollback.h"
+
+QT_BEGIN_NAMESPACE
+
+/*!
+    \class QScopedValueRollback
+    \brief The QScopedValueRollback resets a variable to its previous value on destruction
+    \since 4.8
+    \ingroup misc
+
+    The QScopedAssignment class can be used to revert state when an
+    exception is thrown without needing to write try-catch blocks.
+
+    It can also be used to manage variables that are temporarily set,
+    such as reentrancy guards. By using this class, the variable will
+    be reset whether the function is exited normally, exited early by
+    a return statement, or exited by an exception.
+
+    The template can only be instantiated with a type that supports assignment.
+
+    \sa QScopedPointer
+*/
+
+/*!
+    \fn QScopedValueRollback::QScopedValueRollback(T &var)
+
+    Stores the previous value of var internally, for revert on destruction.
+*/
+
+/*!
+    \fn QScopedValueRollback::~QScopedValueRollback()
+
+    Assigns the previous value to the managed variable.
+    This is the value at construction time, or at the last call to commit()
+*/
+
+/*!
+    \fn void QScopedValueRollback::commit()
+
+    Updates the previous value of the managed variable to its current value.
+*/
+
+QT_END_NAMESPACE