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/****************************************************************************
**
** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the QtXmlPatterns module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL21$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and Digia. For licensing terms and
** conditions see http://qt.digia.com/licensing. For further information
** use the contact form at http://qt.digia.com/contact-us.
**
** 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 or version 3 as published by the Free
** Software Foundation and appearing in the file LICENSE.LGPLv21 and
** LICENSE.LGPLv3 included in the packaging of this file. Please review the
** following information to ensure the GNU Lesser General Public License
** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Digia gives you certain additional
** rights. These rights are described in the Digia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** $QT_END_LICENSE$
**
****************************************************************************/
//
// W A R N I N G
// -------------
//
// This file is not part of the Qt API. It exists purely as an
// implementation detail. This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
#ifndef Patternist_CppCastingHelper_H
#define Patternist_CppCastingHelper_H
#include <QtCore/QtGlobal>
QT_BEGIN_NAMESPACE
namespace QPatternist
{
/**
* @short Provides convenience methods for performing static casts between C++ classes.
*
* In Patternist, it is very common to do up-casts from Expression or Item, which typically
* involves writing messy code. Such an old-way cast looks like this:
*
* @code
* static_cast<const MyClass *>(myInstance.data())->myClassMember()
* @endcode
*
* CppCastingHelper provides the convenience method as() for this, which is functionally
* equivalent to the above code, but simpler:
*
* @code
* myInstance->as<MyClass>()->myClassMember()
* @endcode
*
* The as() function performs a static cast.
*
* By using CppCastingHelper, this is achieved:
*
* - Const correctness is automatically taken care of
* - Less code to write
* - When compiling in debug mode, the as() functions uses a @c dynamic_cast to verify that the
* static casts are properly done, such that sensible error messages are given when the casts
* are invalid. It also traps invalid casts which nevertheless happen to work on a particular
* platform/compiler/hardware architecture.
*
* CppCastingHelper is a template class where the TSubClass parameter must be the class
* inheriting CppCastingHelper. See Item or Expression for demonstration.
*
* @author Frans Englich <frans.englich@nokia.com>
*/
template<typename TSubClass>
class CppCastingHelper
{
public:
/**
* Casts this instance to:
*
* @code
* const TCastTarget *
* @endcode
*
* and returns the result.
*
* When compiled in debug mode, this function perform a @c dynamic_cast, in order to
* check the correctness of the cast.
*/
template<typename TCastTarget>
inline const TCastTarget *as() const
{
#if defined(Patternist_DEBUG) && !defined(Q_CC_XLC)
/* At least on aix-xlc-64, the compiler cries when it sees dynamic_cast. */
Q_ASSERT_X(dynamic_cast<const TCastTarget *>(static_cast<const TSubClass *>(this)),
Q_FUNC_INFO,
"The cast is invalid. This class does not inherit the cast target.");
#endif
return static_cast<const TCastTarget *>(static_cast<const TSubClass *>(this));
}
/**
* Casts this instance to:
*
* @code
* TCastTarget *
* @endcode
*
* and returns the result.
*
* When compiled in debug mode, a @c dynamic_cast is attempted, in order to
* check the correctness of the cast.
*/
template<typename TCastTarget>
inline TCastTarget *as()
{
#if defined(Patternist_DEBUG) && !defined(Q_CC_XLC)
/* At least on aix-xlc-64, the compiler cries when it sees dynamic_cast. */
Q_ASSERT_X(dynamic_cast<TCastTarget *>(static_cast<TSubClass *>(this)),
Q_FUNC_INFO,
"The cast is invalid. This class does not inherit the cast target.");
#endif
return static_cast<TCastTarget *>(static_cast<TSubClass *>(this));
}
protected:
/**
* This constructor is protected because this class must be sub-classed.
*/
inline CppCastingHelper() {}
};
}
QT_END_NAMESPACE
#endif
|
