OptionalItemEvaluator

java.lang.Object
- net.sf.saxon.expr.elab.OptionalItemEvaluator

All Implemented Interfaces:

SequenceEvaluator
```
public class OptionalItemEvaluator
extends java.lang.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

All Methods Instance Methods Concrete Methods
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 Detail
  - OptionalItemEvaluator
```
public OptionalItemEvaluator(ItemEvaluator eval)
```
- Method Detail
  - 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.