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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_NodeComparison_H
51 #define Patternist_NodeComparison_H
52 
53 #include <private/qpaircontainer_p.h>
54 
55 QT_BEGIN_NAMESPACE
56 
57 namespace QPatternist
58 {
59 
60     /**
61      * @short Implements the node comparison operators <tt>\>\></tt>, <tt>\<\<</tt>, and @c is.
62      *
63      * @see <a href="http://www.w3.org/TR/xpath20/#id-node-comparisons">XML Path Language
64      * (XPath) 2.0, 3.5.3 QXmlNodeModelIndex Comparisons</a>
65      * @author Frans Englich <frans.englich@nokia.com>
66      * @ingroup Patternist_expressions
67      */
68     class Q_AUTOTEST_EXPORT NodeComparison : public PairContainer
69     {
70     public:
71         NodeComparison(const Expression::Ptr &operand1,
72                        const QXmlNodeModelIndex::DocumentOrder op,
73                        const Expression::Ptr &operand2);
74 
75         virtual Item evaluateSingleton(const DynamicContext::Ptr &) const;
76         virtual bool evaluateEBV(const DynamicContext::Ptr &) const;
77 
78         virtual SequenceType::List expectedOperandTypes() const;
79 
80         virtual QXmlNodeModelIndex::DocumentOrder operatorID() const;
81         /**
82          * If any operator is the empty sequence, the NodeComparison rewrites
83          * into that, since the empty sequence is always the result in that case.
84          */
85         virtual Expression::Ptr compress(const StaticContext::Ptr &context);
86 
87         /**
88          * @returns either CommonSequenceTypes::ZeroOrOneBoolean or
89          * CommonSequenceTypes::ExactlyOneBoolean depending on the static
90          * cardinality of its operands.
91          */
92         virtual SequenceType::Ptr staticType() const;
93 
94         /**
95          * Determines the string representation for a node comparison operator.
96          *
97          * @returns
98          * - "<<" if @p op is Precedes
99          * - ">>" if @p op is Follows
100          * - "is" if @p op is Is
101          */
102         static QString displayName(const QXmlNodeModelIndex::DocumentOrder op);
103 
104         virtual ExpressionVisitorResult::Ptr accept(const ExpressionVisitor::Ptr &visitor) const;
105     private:
106         enum Result
107         {
108             Empty,
109             True,
110             False
111         };
112         inline Result evaluate(const DynamicContext::Ptr &context) const;
113 
114         const QXmlNodeModelIndex::DocumentOrder m_op;
115 
116     };
117 }
118 
119 QT_END_NAMESPACE
120 
121 #endif
122