net.sf.saxon.value
public class Closure extends Value
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.
Field Summary | |
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protected int | depth |
protected Expression | expression |
protected SequenceIterator | inputIterator |
protected XPathContextMajor | savedXPathContext |
Constructor Summary | |
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Closure()
Constructor should not be called directly, instances should be made using the make() method. |
Method Summary | |
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void | display(int level, NamePool pool, PrintStream out) |
int | getCardinality()
Get the cardinality |
int | getImplementationMethod()
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
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ItemType | getItemType(TypeHierarchy th)
Get the static item type |
int | getSpecialProperties()
Get the static properties of this expression (other than its type). |
boolean | isIndexable()
Determine whether this Closure is indexable |
SequenceIterator | iterate(XPathContext context)
Evaluate the expression in a given context to return an iterator over a sequence |
static Value | make(Expression expression, XPathContext context, int ref)
Construct a Closure by supplying the expression and the set of context variables. |
static Closure | makeIteratorClosure(SequenceIterator iterator)
Construct a Closure over an existing SequenceIterator. |
void | process(XPathContext context)
Process the instruction, without returning any tail calls |
Value | reduce()
Reduce a value to its simplest form. |
Parameters: th
Parameters: context the evaluation context. This is ignored; we use the context saved as part of the Closure instead.
Parameters: context The dynamic context, giving access to the current node, the current variables, etc.