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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_FirstItemPredicate_H
53 #define Patternist_FirstItemPredicate_H
55 #include <private/qsinglecontainer_p.h>
64 * @short A predicate that always selects the first item from its sequence.
66 * FirstItemPredicate corresponds exactly to the predicate
67 * in the expression <tt>input[1]</tt>.
69 * @author Frans Englich <frans.englich@nokia.com>
70 * @ingroup Patternist_expressions
72 class FirstItemPredicate : public SingleContainer
76 * Creates a FirstItemPredicate that filters @p source.
78 FirstItemPredicate(const Expression::Ptr &source);
81 * @returns the first item, if any, from evaluating the source expression.
83 virtual Item evaluateSingleton(const DynamicContext::Ptr &) const;
86 * @returns a list containing one CommonSequenceTypes::ZeroOrMoreItems instance.
88 virtual SequenceType::List expectedOperandTypes() const;
91 * @returns a SequenceType where the item type is the same as the source expression
92 * and where the cardinality is either Cardinality::zeroOrOne() or Cardinality::exactlyOne(),
93 * depending on the source expression.
95 virtual SequenceType::Ptr staticType() const;
96 virtual ExpressionVisitorResult::Ptr accept(const ExpressionVisitor::Ptr &visitor) const;
99 * Rewrites <tt>expression[1][1]</tt> into <tt>expression[1]</tt>.
101 virtual Expression::Ptr compress(const StaticContext::Ptr &context);
104 * @returns always IDFirstItemPredicate.
106 virtual ID id() const;