net.sf.saxon.value
Class Closure
- Serializable, SequenceIterable, ValueRepresentation
A Closure 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.
This Closure is designed for use when the value is only read once. If the value
is read more than once, a new iterator over the underlying expression is obtained
each time: this may (for example in the case of a filter expression) involve
significant re-calculation.
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.
Closure() - Constructor should not be called directly, instances should be made using the make() method.
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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 |
Closure
public Closure()
Constructor should not be called directly, instances should be made using the make() method.
getCardinality
public int getCardinality()
Get the cardinality
- getCardinality in interface Value
make
public static Value make(Expression expression,
XPathContext context,
int ref)
throws XPathException
Construct a Closure by supplying the expression and the set of context variables.
expression
- the expression to be lazily evaluatedcontext
- the dynamic context of the expression including for example the variables
on which it dependsref
- the number of references to the value being lazily evaluated; this affects
the kind of Closure that is created
- the Closure, a virtual value that can later be materialized when its content is required
makeIteratorClosure
public static Closure makeIteratorClosure(SequenceIterator iterator)
Construct a Closure over an existing SequenceIterator. This is used when an extension function
returns a SequenceIterator as its result (it replaces the old SequenceIntent class for this
purpose). There is no known expression in this case. Note that the caller must
ensure this is a "clean" iterator: it must be positioned at the start, and must
not be shared by anyone else.
iterator
- the supplied iterator
- the Closure over this iterator
process
public void process(XPathContext context)
throws XPathException
Process the instruction, without returning any tail calls
- process in interface Value
context
- The dynamic context, giving access to the current node,
the current variables, etc.
reduce
public Value reduce()
throws XPathException
Reduce a value to its simplest form. If the value is a closure or some other form of deferred value
such as a FunctionCallPackage, then it is reduced to a SequenceExtent. If it is a SequenceExtent containing
a single item, then it is reduced to that item. One consequence that is exploited by class FilterExpression
is that if the value is a singleton numeric value, then the result will be an instance of NumericValue
- reduce in interface Value