Package net.sf.saxon.expr.elab

Class OptionalItemEvaluator

java.lang.Object

net.sf.saxon.expr.elab.OptionalItemEvaluator

All Implemented Interfaces:

SequenceEvaluator

public class OptionalItemEvaluator
extends Object
implements SequenceEvaluator

A SequenceEvaluator for expressions that return a sequence of zero or one items. Unlike the SingleItemEvaluator, it checks whether the underlying ItemEvaluator has returned null, and if so, returns an empty sequence rather than a single item.

Constructor Summary

Constructors

Constructor	Description
OptionalItemEvaluator(ItemEvaluator eval)

Method Summary

Modifier and Type	Method	Description
Sequence	evaluate(XPathContext context)	Evaluate a construct to produce a value (which might be a lazily evaluated Sequence)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

OptionalItemEvaluator

public OptionalItemEvaluator(ItemEvaluator eval)

Method Details

evaluate

public Sequence evaluate(XPathContext context)
                  throws XPathException

Evaluate a construct to produce a value (which might be a lazily evaluated Sequence)

Specified by:

evaluate in interface SequenceEvaluator

Parameters:

context - the evaluation context

Returns:

a Sequence (not necessarily grounded). This will be an EmptySequence if the underlying ItemEvaluator returns null.

Throws:

XPathException - if a dynamic error occurs during the evaluation.