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/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the QtXmlPatterns 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 either Technology Preview License Agreement or the
** Beta Release License Agreement.
**
** 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
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain
** additional rights. These rights are described in the Nokia Qt LGPL
** Exception version 1.0, included in the file LGPL_EXCEPTION.txt in this
** package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file.  Please review the following information to
** ensure the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
** If you are unsure which license is appropriate for your use, please
** contact the sales department at http://qt.nokia.com/contact.
** $QT_END_LICENSE$
**
****************************************************************************/

//
//  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_HEADER

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

QT_END_HEADER

#endif