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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_FirstItemPredicate_H
51#define Patternist_FirstItemPredicate_H
52
53#include <private/qsinglecontainer_p.h>
54
55QT_BEGIN_NAMESPACE
56
57namespace QPatternist
58{
59 /**
60 * @short A predicate that always selects the first item from its sequence.
61 *
62 * FirstItemPredicate corresponds exactly to the predicate
63 * in the expression <tt>input[1]</tt>.
64 *
65 * @author Frans Englich <frans.englich@nokia.com>
66 * @ingroup Patternist_expressions
67 */
68 class FirstItemPredicate : public SingleContainer
69 {
70 public:
71 /**
72 * Creates a FirstItemPredicate that filters @p source.
73 */
74 FirstItemPredicate(const Expression::Ptr &source);
75
76 /**
77 * @returns the first item, if any, from evaluating the source expression.
78 */
79 virtual Item evaluateSingleton(const DynamicContext::Ptr &) const;
80
81 /**
82 * @returns a list containing one CommonSequenceTypes::ZeroOrMoreItems instance.
83 */
84 virtual SequenceType::List expectedOperandTypes() const;
85
86 /**
87 * @returns a SequenceType where the item type is the same as the source expression
88 * and where the cardinality is either Cardinality::zeroOrOne() or Cardinality::exactlyOne(),
89 * depending on the source expression.
90 */
91 virtual SequenceType::Ptr staticType() const;
92 virtual ExpressionVisitorResult::Ptr accept(const ExpressionVisitor::Ptr &visitor) const;
93
94 /**
95 * Rewrites <tt>expression[1][1]</tt> into <tt>expression[1]</tt>.
96 */
97 virtual Expression::Ptr compress(const StaticContext::Ptr &context);
98
99 /**
100 * @returns always IDFirstItemPredicate.
101 */
102 virtual ID id() const;
103 };
104}
105
106QT_END_NAMESPACE
107
108#endif
109

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