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1 /**************************************************************************** |
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2 ** |
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3 ** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies). |
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4 ** All rights reserved. |
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5 ** Contact: Nokia Corporation (qt-info@nokia.com) |
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6 ** |
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7 ** This file is part of the QtXmlPatterns module of the Qt Toolkit. |
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8 ** |
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9 ** $QT_BEGIN_LICENSE:LGPL$ |
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10 ** No Commercial Usage |
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11 ** This file contains pre-release code and may not be distributed. |
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12 ** You may use this file in accordance with the terms and conditions |
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13 ** contained in the Technology Preview License Agreement accompanying |
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14 ** this package. |
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15 ** |
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16 ** GNU Lesser General Public License Usage |
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17 ** Alternatively, this file may be used under the terms of the GNU Lesser |
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18 ** General Public License version 2.1 as published by the Free Software |
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19 ** Foundation and appearing in the file LICENSE.LGPL included in the |
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20 ** packaging of this file. Please review the following information to |
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21 ** ensure the GNU Lesser General Public License version 2.1 requirements |
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22 ** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. |
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23 ** |
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24 ** In addition, as a special exception, Nokia gives you certain additional |
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25 ** rights. These rights are described in the Nokia Qt LGPL Exception |
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26 ** version 1.1, included in the file LGPL_EXCEPTION.txt in this package. |
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27 ** |
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28 ** If you have questions regarding the use of this file, please contact |
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29 ** Nokia at qt-info@nokia.com. |
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30 ** |
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31 ** |
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32 ** |
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33 ** |
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34 ** |
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35 ** |
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36 ** |
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37 ** |
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38 ** $QT_END_LICENSE$ |
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39 ** |
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40 ****************************************************************************/ |
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41 |
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42 // |
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43 // W A R N I N G |
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44 // ------------- |
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45 // |
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46 // This file is not part of the Qt API. It exists purely as an |
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47 // implementation detail. This header file may change from version to |
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48 // version without notice, or even be removed. |
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49 // |
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50 // We mean it. |
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51 |
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52 #ifndef Patternist_CppCastingHelper_H |
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53 #define Patternist_CppCastingHelper_H |
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54 |
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55 #include <QtCore/QtGlobal> |
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56 |
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57 QT_BEGIN_HEADER |
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58 |
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59 QT_BEGIN_NAMESPACE |
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60 |
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61 namespace QPatternist |
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62 { |
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63 /** |
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64 * @short Provides convenience methods for performing static casts between C++ classes. |
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65 * |
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66 * In Patternist, it is very common to do up-casts from Expression or Item, which typically |
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67 * involves writing messy code. Such an old-way cast looks like this: |
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68 * |
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69 * @code |
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70 * static_cast<const MyClass *>(myInstance.data())->myClassMember() |
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71 * @endcode |
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72 * |
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73 * CppCastingHelper provides the convenience method as() for this, which is functionally |
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74 * equivalent to the above code, but simpler: |
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75 * |
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76 * @code |
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77 * myInstance->as<MyClass>()->myClassMember() |
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78 * @endcode |
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79 * |
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80 * The as() function performs a static cast. |
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81 * |
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82 * By using CppCastingHelper, this is achieved: |
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83 * |
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84 * - Const correctness is automatically taken care of |
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85 * - Less code to write |
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86 * - When compiling in debug mode, the as() functions uses a @c dynamic_cast to verify that the |
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87 * static casts are properly done, such that sensible error messages are given when the casts |
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88 * are invalid. It also traps invalid casts which nevertheless happen to work on a particular |
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89 * platform/compiler/hardware architecture. |
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90 * |
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91 * CppCastingHelper is a template class where the TSubClass parameter must be the class |
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92 * inheriting CppCastingHelper. See Item or Expression for demonstration. |
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93 * |
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94 * @author Frans Englich <frans.englich@nokia.com> |
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95 */ |
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96 template<typename TSubClass> |
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97 class CppCastingHelper |
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98 { |
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99 public: |
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100 |
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101 /** |
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102 * Casts this instance to: |
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103 * |
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104 * @code |
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105 * const TCastTarget * |
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106 * @endcode |
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107 * |
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108 * and returns the result. |
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109 * |
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110 * When compiled in debug mode, this function perform a @c dynamic_cast, in order to |
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111 * check the correctness of the cast. |
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112 */ |
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113 template<typename TCastTarget> |
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114 inline const TCastTarget *as() const |
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115 { |
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116 #if defined(Patternist_DEBUG) && !defined(Q_CC_XLC) |
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117 /* At least on aix-xlc-64, the compiler cries when it sees dynamic_cast. */ |
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118 Q_ASSERT_X(dynamic_cast<const TCastTarget *>(static_cast<const TSubClass *>(this)), |
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119 Q_FUNC_INFO, |
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120 "The cast is invalid. This class does not inherit the cast target."); |
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121 #endif |
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122 return static_cast<const TCastTarget *>(static_cast<const TSubClass *>(this)); |
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123 } |
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124 |
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125 /** |
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126 * Casts this instance to: |
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127 * |
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128 * @code |
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129 * TCastTarget * |
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130 * @endcode |
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131 * |
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132 * and returns the result. |
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133 * |
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134 * When compiled in debug mode, a @c dynamic_cast is attempted, in order to |
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135 * check the correctness of the cast. |
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136 */ |
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137 template<typename TCastTarget> |
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138 inline TCastTarget *as() |
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139 { |
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140 #if defined(Patternist_DEBUG) && !defined(Q_CC_XLC) |
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141 /* At least on aix-xlc-64, the compiler cries when it sees dynamic_cast. */ |
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142 Q_ASSERT_X(dynamic_cast<TCastTarget *>(static_cast<TSubClass *>(this)), |
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143 Q_FUNC_INFO, |
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144 "The cast is invalid. This class does not inherit the cast target."); |
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145 #endif |
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146 return static_cast<TCastTarget *>(static_cast<TSubClass *>(this)); |
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147 } |
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148 |
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149 protected: |
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150 /** |
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151 * This constructor is protected because this class must be sub-classed. |
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152 */ |
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153 inline CppCastingHelper() {} |
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154 }; |
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155 } |
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156 |
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157 QT_END_NAMESPACE |
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158 |
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159 QT_END_HEADER |
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160 |
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161 #endif |