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39 | |
40 | // |
41 | // W A R N I N G |
42 | // ------------- |
43 | // |
44 | // This file is not part of the Qt API. It exists purely as an |
45 | // implementation detail. This header file may change from version to |
46 | // version without notice, or even be removed. |
47 | // |
48 | // We mean it. |
49 | |
50 | #ifndef Patternist_CppCastingHelper_H |
51 | #define Patternist_CppCastingHelper_H |
52 | |
53 | #include <QtCore/QtGlobal> |
54 | |
55 | QT_BEGIN_NAMESPACE |
56 | |
57 | namespace QPatternist |
58 | { |
59 | /** |
60 | * @short Provides convenience methods for performing static casts between C++ classes. |
61 | * |
62 | * In Patternist, it is very common to do up-casts from Expression or Item, which typically |
63 | * involves writing messy code. Such an old-way cast looks like this: |
64 | * |
65 | * @code |
66 | * static_cast<const MyClass *>(myInstance.data())->myClassMember() |
67 | * @endcode |
68 | * |
69 | * CppCastingHelper provides the convenience method as() for this, which is functionally |
70 | * equivalent to the above code, but simpler: |
71 | * |
72 | * @code |
73 | * myInstance->as<MyClass>()->myClassMember() |
74 | * @endcode |
75 | * |
76 | * The as() function performs a static cast. |
77 | * |
78 | * By using CppCastingHelper, this is achieved: |
79 | * |
80 | * - Const correctness is automatically taken care of |
81 | * - Less code to write |
82 | * - When compiling in debug mode, the as() functions uses a @c dynamic_cast to verify that the |
83 | * static casts are properly done, such that sensible error messages are given when the casts |
84 | * are invalid. It also traps invalid casts which nevertheless happen to work on a particular |
85 | * platform/compiler/hardware architecture. |
86 | * |
87 | * CppCastingHelper is a template class where the TSubClass parameter must be the class |
88 | * inheriting CppCastingHelper. See Item or Expression for demonstration. |
89 | * |
90 | * @author Frans Englich <frans.englich@nokia.com> |
91 | */ |
92 | template<typename TSubClass> |
93 | class CppCastingHelper |
94 | { |
95 | public: |
96 | |
97 | /** |
98 | * Casts this instance to: |
99 | * |
100 | * @code |
101 | * const TCastTarget * |
102 | * @endcode |
103 | * |
104 | * and returns the result. |
105 | * |
106 | * When compiled in debug mode, this function perform a @c dynamic_cast, in order to |
107 | * check the correctness of the cast. |
108 | */ |
109 | template<typename TCastTarget> |
110 | inline const TCastTarget *as() const |
111 | { |
112 | #if defined(Patternist_DEBUG) && !defined(Q_CC_XLC) |
113 | /* At least on aix-xlc-64, the compiler cries when it sees dynamic_cast. */ |
114 | Q_ASSERT_X(dynamic_cast<const TCastTarget *>(static_cast<const TSubClass *>(this)), |
115 | Q_FUNC_INFO, |
116 | "The cast is invalid. This class does not inherit the cast target." ); |
117 | #endif |
118 | return static_cast<const TCastTarget *>(static_cast<const TSubClass *>(this)); |
119 | } |
120 | |
121 | /** |
122 | * Casts this instance to: |
123 | * |
124 | * @code |
125 | * TCastTarget * |
126 | * @endcode |
127 | * |
128 | * and returns the result. |
129 | * |
130 | * When compiled in debug mode, a @c dynamic_cast is attempted, in order to |
131 | * check the correctness of the cast. |
132 | */ |
133 | template<typename TCastTarget> |
134 | inline TCastTarget *as() |
135 | { |
136 | #if defined(Patternist_DEBUG) && !defined(Q_CC_XLC) |
137 | /* At least on aix-xlc-64, the compiler cries when it sees dynamic_cast. */ |
138 | Q_ASSERT_X(dynamic_cast<TCastTarget *>(static_cast<TSubClass *>(this)), |
139 | Q_FUNC_INFO, |
140 | "The cast is invalid. This class does not inherit the cast target." ); |
141 | #endif |
142 | return static_cast<TCastTarget *>(static_cast<TSubClass *>(this)); |
143 | } |
144 | |
145 | protected: |
146 | /** |
147 | * This constructor is protected because this class must be sub-classed. |
148 | */ |
149 | inline CppCastingHelper() {} |
150 | }; |
151 | } |
152 | |
153 | QT_END_NAMESPACE |
154 | |
155 | #endif |
156 | |