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| |
| // |
| // 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 |