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Diffstat (limited to 'src/xmlpatterns/utils/qcppcastinghelper_p.h')
| -rw-r--r-- | src/xmlpatterns/utils/qcppcastinghelper_p.h | 161 |
1 files changed, 161 insertions, 0 deletions
diff --git a/src/xmlpatterns/utils/qcppcastinghelper_p.h b/src/xmlpatterns/utils/qcppcastinghelper_p.h new file mode 100644 index 0000000000..7979bf0bf3 --- /dev/null +++ b/src/xmlpatterns/utils/qcppcastinghelper_p.h @@ -0,0 +1,161 @@ +/**************************************************************************** +** +** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies). +** Contact: Qt Software Information (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 qt-sales@nokia.com. +** $QT_END_LICENSE$ +** +****************************************************************************/ + +// +// 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 <fenglich@trolltech.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 |