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46 // This file is not part of the Qt API. It exists purely as an
47 // implementation detail. This header file may change from version to
48 // version without notice, or even be removed.
52 #ifndef Patternist_EvaluationCache_H
53 #define Patternist_EvaluationCache_H
55 #include "qcachingiterator_p.h"
56 #include "qcommonsequencetypes_p.h"
57 #include "qnodebuilder_p.h"
58 #include "qoperandsiterator_p.h"
59 #include "qsinglecontainer_p.h"
60 #include "qvariabledeclaration_p.h"
69 * @short Evaluates to the same result as its operand, but ensures the
70 * operand is evaluated once even if this Expression is evaluated several
73 * EvaluationCache does this in a pipelined way, by delivering items from
74 * its cache, which is stored in the DynamicContext. If the cache has less
75 * items than what the caller requests, EvaluationCache continues to
76 * deliver but this time from the source, which it also populates into the
79 * EvaluationCache is used as an optimization in order to avoid running
80 * expensive code paths multiple times, but also is sometimes a necessity:
81 * for instance, when objects must be unique, such as potentially in the
82 * case of node identity.
84 * EvaluationCache is in particular used for variables, whose sole purpose
85 * is to store it once(at least conceptually) and then use it in multiple
88 * In some cases an EvaluationCache isn't necessary. For instance, when a
89 * variable is only referenced once. In those cases EvaluationCache removes
90 * itself as an optimization; implemented in compress().
92 * @author Frans Englich <frans.englich@nokia.com>
93 * @ingroup Patternist_expressions
95 template<bool IsForGlobal>
96 class EvaluationCache : public SingleContainer
99 EvaluationCache(const Expression::Ptr &operand,
100 const VariableDeclaration::Ptr &varDecl,
101 const VariableSlotID slot);
103 virtual Item evaluateSingleton(const DynamicContext::Ptr &context) const;
104 virtual Item::Iterator::Ptr evaluateSequence(const DynamicContext::Ptr &context) const;
105 virtual Expression::Ptr compress(const StaticContext::Ptr &context);
107 virtual SequenceType::Ptr staticType() const;
110 * The first operand must be exactly one @c xs:string.
112 virtual SequenceType::List expectedOperandTypes() const;
114 virtual ExpressionVisitorResult::Ptr accept(const ExpressionVisitor::Ptr &visitor) const;
115 virtual Properties properties() const;
116 virtual Expression::Ptr typeCheck(const StaticContext::Ptr &context,
117 const SequenceType::Ptr &reqType);
118 virtual const SourceLocationReflection *actualReflection() const;
120 inline VariableSlotID slot() const
126 static DynamicContext::Ptr topFocusContext(const DynamicContext::Ptr &context);
127 const VariableDeclaration::Ptr m_declaration;
129 * This variable must not be called m_slot. If it so, a compiler bug on
130 * HP-UX-aCC-64 is triggered in the constructor initializor. See the
131 * preprocessor output.
133 * Note that this is the cache slot, and is disjoint to any variable's
136 const VariableSlotID m_varSlot;
139 #include "qevaluationcache.cpp"