net.sf.saxon.value

Class SingletonClosure

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.

Constructor Summary
SingletonClosure(Expression exp, XPathContext context)
Constructor should not be called directly, instances should be made using the make() method.
Method Summary
ItemasItem()
Return the value in the form of an Item
intgetLength()
Get the length of the sequence
ItemitemAt(int n)
Get the n'th item in the sequence (starting from 0).
SequenceIteratoriterate()
Evaluate the expression in a given context to return an iterator over a sequence
Valuematerialize()
Return a value containing all the items in the sequence returned by this SequenceIterator
voidprocess(XPathContext context)
Process the expression by writing the value to the current Receiver

Constructor Detail

SingletonClosure

public SingletonClosure(Expression exp, XPathContext context)
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 Detail

asItem

public Item asItem()
Return the value in the form of an Item

Returns: the value in the form of an Item

getLength

public int getLength()
Get the length of the sequence

itemAt

public Item itemAt(int n)
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

iterate

public SequenceIterator iterate()
Evaluate the expression in a given context to return an iterator over a sequence

materialize

public Value materialize()
Return a value containing all the items in the sequence returned by this SequenceIterator

Returns: the corresponding value

process

public void process(XPathContext context)
Process the expression by writing the value to the current Receiver

Parameters: context The dynamic context, giving access to the current node, the current variables, etc.