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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_EvaluationCache_H |
51 | #define Patternist_EvaluationCache_H |
52 | |
53 | #include <private/qcachingiterator_p.h> |
54 | #include <private/qcommonsequencetypes_p.h> |
55 | #include <private/qnodebuilder_p.h> |
56 | #include <private/qoperandsiterator_p.h> |
57 | #include <private/qsinglecontainer_p.h> |
58 | #include <private/qvariabledeclaration_p.h> |
59 | |
60 | QT_BEGIN_NAMESPACE |
61 | |
62 | namespace QPatternist |
63 | { |
64 | /** |
65 | * @short Evaluates to the same result as its operand, but ensures the |
66 | * operand is evaluated once even if this Expression is evaluated several |
67 | * times. |
68 | * |
69 | * EvaluationCache does this in a pipelined way, by delivering items from |
70 | * its cache, which is stored in the DynamicContext. If the cache has less |
71 | * items than what the caller requests, EvaluationCache continues to |
72 | * deliver but this time from the source, which it also populates into the |
73 | * cache. |
74 | * |
75 | * EvaluationCache is used as an optimization in order to avoid running |
76 | * expensive code paths multiple times, but also is sometimes a necessity: |
77 | * for instance, when objects must be unique, such as potentially in the |
78 | * case of node identity. |
79 | * |
80 | * EvaluationCache is in particular used for variables, whose sole purpose |
81 | * is to store it once(at least conceptually) and then use it in multiple |
82 | * places. |
83 | * |
84 | * In some cases an EvaluationCache isn't necessary. For instance, when a |
85 | * variable is only referenced once. In those cases EvaluationCache removes |
86 | * itself as an optimization; implemented in compress(). |
87 | * |
88 | * @author Frans Englich <frans.englich@nokia.com> |
89 | * @ingroup Patternist_expressions |
90 | */ |
91 | template<bool IsForGlobal> |
92 | class EvaluationCache : public SingleContainer |
93 | { |
94 | public: |
95 | EvaluationCache(const Expression::Ptr &operand, |
96 | const VariableDeclaration::Ptr &varDecl, |
97 | const VariableSlotID slot); |
98 | |
99 | virtual Item evaluateSingleton(const DynamicContext::Ptr &context) const; |
100 | virtual Item::Iterator::Ptr evaluateSequence(const DynamicContext::Ptr &context) const; |
101 | virtual Expression::Ptr compress(const StaticContext::Ptr &context); |
102 | |
103 | virtual SequenceType::Ptr staticType() const; |
104 | |
105 | /** |
106 | * The first operand must be exactly one @c xs:string. |
107 | */ |
108 | virtual SequenceType::List expectedOperandTypes() const; |
109 | |
110 | virtual ExpressionVisitorResult::Ptr accept(const ExpressionVisitor::Ptr &visitor) const; |
111 | virtual Properties properties() const; |
112 | virtual Expression::Ptr typeCheck(const StaticContext::Ptr &context, |
113 | const SequenceType::Ptr &reqType); |
114 | virtual const SourceLocationReflection *actualReflection() const; |
115 | |
116 | inline VariableSlotID slot() const |
117 | { |
118 | return m_varSlot; |
119 | } |
120 | |
121 | private: |
122 | static DynamicContext::Ptr topFocusContext(const DynamicContext::Ptr &context); |
123 | const VariableDeclaration::Ptr m_declaration; |
124 | /** |
125 | * This variable must not be called m_slot. If it so, a compiler bug on |
126 | * HP-UX-aCC-64 is triggered in the constructor initializor. See the |
127 | * preprocessor output. |
128 | * |
129 | * Note that this is the cache slot, and is disjoint to any variable's |
130 | * regular slot. |
131 | */ |
132 | const VariableSlotID m_varSlot; |
133 | }; |
134 | |
135 | #include "qevaluationcache_tpl_p.h" |
136 | } |
137 | |
138 | QT_END_NAMESPACE |
139 | |
140 | #endif |
141 | |