net.sf.saxon.value

Class SingletonClosure

Implemented Interfaces:
Serializable, SequenceIterable, ValueRepresentation

public class SingletonClosure
extends Closure

A SingletonClosure represents a value that has not yet been evaluated: the value is represented by an expression, together with saved values of all the context variables that the expression depends on. The value of a SingletonClosure is always either a single item or an empty sequence.

The expression may depend on local variables and on the context item; these values are held in the saved XPathContext object that is kept as part of the Closure, and they will always be read from that object. The expression may also depend on global variables; these are unchanging, so they can be read from the Bindery in the normal way. Expressions that depend on other contextual information, for example the values of position(), last(), current(), current-group(), should not be evaluated using this mechanism: they should always be evaluated eagerly. This means that the Closure does not need to keep a copy of these context variables.

Field Summary

Fields inherited from class net.sf.saxon.value.Closure

depth, expression, inputIterator, savedXPathContext

Fields inherited from class net.sf.saxon.value.Value

EMPTY_CLASS_ARRAY, INDETERMINATE_ORDERING

Fields inherited from interface net.sf.saxon.om.ValueRepresentation

EMPTY_VALUE_ARRAY

Constructor Summary

SingletonClosure(Expression exp, XPathContext context)
Constructor should not be called directly, instances should be made using the make() method.

Method Summary

Item
asItem()
Return the value in the form of an Item
int
getLength()
Get the length of the sequence
Item
itemAt(int n)
Get the n'th item in the sequence (starting from 0).
SequenceIterator
iterate()
Evaluate the expression in a given context to return an iterator over a sequence
Value
materialize()
Return a value containing all the items in the sequence returned by this SequenceIterator
void
process(XPathContext context)
Process the expression by writing the value to the current Receiver

Methods inherited from class net.sf.saxon.value.Closure

getCardinality, getItemType, iterate, make, makeIteratorClosure, process, reduce, saveContext

Methods inherited from class net.sf.saxon.value.Value

asItem, asItem, asIterator, asValue, checkPermittedContents, convertJavaObjectToXPath, convertToJava, convertToJava, effectiveBooleanValue, equals, fromItem, getCanonicalLexicalRepresentation, getCardinality, getItemType, getIterator, getLength, getSchemaComparable, getStringValue, getStringValueCS, itemAt, iterate, iterate, makeQNameValue, process, reduce, stringToNumber, toString

Constructor Details

SingletonClosure

public SingletonClosure(Expression exp,
                        XPathContext context)
            throws XPathException
Constructor should not be called directly, instances should be made using the make() method.
Parameters:
exp - the expression to be lazily evaluated
context - the context in which the expression should be evaluated

Method Details

asItem

public Item asItem()
            throws XPathException
Return the value in the form of an Item
Overrides:
asItem in interface Value
Returns:
the value in the form of an Item

getLength

public int getLength()
            throws XPathException
Get the length of the sequence
Overrides:
getLength in interface Value

itemAt

public Item itemAt(int n)
            throws XPathException
Get the n'th item in the sequence (starting from 0). This is defined for all SequenceValues, but its real benefits come for a SequenceValue stored extensionally
Overrides:
itemAt in interface Value

iterate

public SequenceIterator iterate()
            throws XPathException
Evaluate the expression in a given context to return an iterator over a sequence
Overrides:
iterate in interface Closure

materialize

public Value materialize()
            throws XPathException
Return a value containing all the items in the sequence returned by this SequenceIterator
Returns:
the corresponding value

process

public void process(XPathContext context)
            throws XPathException
Process the expression by writing the value to the current Receiver
Overrides:
process in interface Closure
Parameters:
context - The dynamic context, giving access to the current node, the current variables, etc.