Long live Qt 4.5!

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+/****************************************************************************
+**
+** 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