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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
60QT_BEGIN_NAMESPACE
61
62namespace 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
138QT_END_NAMESPACE
139
140#endif
141

source code of qtxmlpatterns/src/xmlpatterns/expr/qevaluationcache_p.h