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39
40#include "qcommonsequencetypes_p.h"
41#include "qgenericsequencetype_p.h"
42
43#include "qfirstitempredicate_p.h"
44
45QT_BEGIN_NAMESPACE
46
47using namespace QPatternist;
48
49FirstItemPredicate::FirstItemPredicate(const Expression::Ptr &source) : SingleContainer(source)
50{
51}
52
53Item FirstItemPredicate::evaluateSingleton(const DynamicContext::Ptr &context) const
54{
55 /* If our operand allows the empty sequence, this function can return Item(), otherwise
56 * it returns the first item. As simple as that. */
57 return m_operand->evaluateSequence(context)->next();
58}
59
60SequenceType::Ptr FirstItemPredicate::staticType() const
61{
62 const SequenceType::Ptr t(m_operand->staticType());
63 return makeGenericSequenceType(itemType: t->itemType(), cardinality: t->cardinality().toWithoutMany());
64}
65
66Expression::Ptr FirstItemPredicate::compress(const StaticContext::Ptr &context)
67{
68 const Expression::Ptr me(SingleContainer::compress(context));
69 if(me != this)
70 return me;
71
72 if(m_operand->is(i: IDFirstItemPredicate))
73 m_operand = m_operand->operands().first();
74
75 return me;
76}
77
78SequenceType::List FirstItemPredicate::expectedOperandTypes() const
79{
80 SequenceType::List result;
81 result.append(t: CommonSequenceTypes::ZeroOrMoreItems);
82 return result;
83}
84
85ExpressionVisitorResult::Ptr FirstItemPredicate::accept(const ExpressionVisitor::Ptr &visitor) const
86{
87 return visitor->visit(this);
88}
89
90Expression::ID FirstItemPredicate::id() const
91{
92 return IDFirstItemPredicate;
93}
94
95QT_END_NAMESPACE
96

source code of qtxmlpatterns/src/xmlpatterns/expr/qfirstitempredicate.cpp