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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_EvaluationCache_H |
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53 #define Patternist_EvaluationCache_H |
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54 |
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55 #include "qcachingiterator_p.h" |
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56 #include "qcommonsequencetypes_p.h" |
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57 #include "qnodebuilder_p.h" |
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58 #include "qoperandsiterator_p.h" |
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59 #include "qsinglecontainer_p.h" |
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60 #include "qvariabledeclaration_p.h" |
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61 |
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62 QT_BEGIN_HEADER |
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63 |
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64 QT_BEGIN_NAMESPACE |
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65 |
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66 namespace QPatternist |
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67 { |
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68 /** |
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69 * @short Evaluates to the same result as its operand, but ensures the |
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70 * operand is evaluated once even if this Expression is evaluated several |
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71 * times. |
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72 * |
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73 * EvaluationCache does this in a pipelined way, by delivering items from |
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74 * its cache, which is stored in the DynamicContext. If the cache has less |
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75 * items than what the caller requests, EvaluationCache continues to |
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76 * deliver but this time from the source, which it also populates into the |
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77 * cache. |
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78 * |
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79 * EvaluationCache is used as an optimization in order to avoid running |
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80 * expensive code paths multiple times, but also is sometimes a necessity: |
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81 * for instance, when objects must be unique, such as potentially in the |
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82 * case of node identity. |
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83 * |
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84 * EvaluationCache is in particular used for variables, whose sole purpose |
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85 * is to store it once(at least conceptually) and then use it in multiple |
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86 * places. |
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87 * |
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88 * In some cases an EvaluationCache isn't necessary. For instance, when a |
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89 * variable is only referenced once. In those cases EvaluationCache removes |
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90 * itself as an optimization; implemented in compress(). |
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91 * |
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92 * @author Frans Englich <frans.englich@nokia.com> |
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93 * @ingroup Patternist_expressions |
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94 */ |
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95 template<bool IsForGlobal> |
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96 class EvaluationCache : public SingleContainer |
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97 { |
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98 public: |
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99 EvaluationCache(const Expression::Ptr &operand, |
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100 const VariableDeclaration::Ptr &varDecl, |
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101 const VariableSlotID slot); |
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102 |
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103 virtual Item evaluateSingleton(const DynamicContext::Ptr &context) const; |
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104 virtual Item::Iterator::Ptr evaluateSequence(const DynamicContext::Ptr &context) const; |
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105 virtual Expression::Ptr compress(const StaticContext::Ptr &context); |
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106 |
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107 virtual SequenceType::Ptr staticType() const; |
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108 |
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109 /** |
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110 * The first operand must be exactly one @c xs:string. |
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111 */ |
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112 virtual SequenceType::List expectedOperandTypes() const; |
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113 |
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114 virtual ExpressionVisitorResult::Ptr accept(const ExpressionVisitor::Ptr &visitor) const; |
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115 virtual Properties properties() const; |
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116 virtual Expression::Ptr typeCheck(const StaticContext::Ptr &context, |
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117 const SequenceType::Ptr &reqType); |
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118 virtual const SourceLocationReflection *actualReflection() const; |
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119 |
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120 inline VariableSlotID slot() const |
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121 { |
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122 return m_varSlot; |
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123 } |
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124 |
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125 private: |
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126 static DynamicContext::Ptr topFocusContext(const DynamicContext::Ptr &context); |
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127 const VariableDeclaration::Ptr m_declaration; |
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128 /** |
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129 * This variable must not be called m_slot. If it so, a compiler bug on |
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130 * HP-UX-aCC-64 is triggered in the constructor initializor. See the |
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131 * preprocessor output. |
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132 * |
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133 * Note that this is the cache slot, and is disjoint to any variable's |
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134 * regular slot. |
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135 */ |
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136 const VariableSlotID m_varSlot; |
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137 }; |
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138 |
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139 #include "qevaluationcache.cpp" |
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140 } |
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141 |
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142 QT_END_NAMESPACE |
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143 |
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144 QT_END_HEADER |
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145 |
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146 #endif |