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42 #include "qcommonsequencetypes_p.h"
43 #include "qgenericsequencetype_p.h"
45 #include "qfirstitempredicate_p.h"
49 using namespace QPatternist;
51 FirstItemPredicate::FirstItemPredicate(const Expression::Ptr &source) : SingleContainer(source)
55 Item FirstItemPredicate::evaluateSingleton(const DynamicContext::Ptr &context) const
57 /* If our operand allows the empty sequence, this function can return Item(), otherwise
58 * it returns the first item. As simple as that. */
59 return m_operand->evaluateSequence(context)->next();
62 SequenceType::Ptr FirstItemPredicate::staticType() const
64 const SequenceType::Ptr t(m_operand->staticType());
65 return makeGenericSequenceType(t->itemType(), t->cardinality().toWithoutMany());
68 Expression::Ptr FirstItemPredicate::compress(const StaticContext::Ptr &context)
70 const Expression::Ptr me(SingleContainer::compress(context));
74 if(m_operand->is(IDFirstItemPredicate))
75 m_operand = m_operand->operands().first();
80 SequenceType::List FirstItemPredicate::expectedOperandTypes() const
82 SequenceType::List result;
83 result.append(CommonSequenceTypes::ZeroOrMoreItems);
87 ExpressionVisitorResult::Ptr FirstItemPredicate::accept(const ExpressionVisitor::Ptr &visitor) const
89 return visitor->visit(this);
92 Expression::ID FirstItemPredicate::id() const
94 return IDFirstItemPredicate;