public class Closure extends java.lang.Object implements Sequence, ContextOriginator
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.
Modifier and Type | Field and Description |
---|---|
protected int |
depth |
protected Expression |
expression |
protected SequenceIterator |
inputIterator |
protected XPathContextMajor |
savedXPathContext |
Constructor and Description |
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Closure()
Constructor should not be called directly, instances should be made using the make() method.
|
Modifier and Type | Method and Description |
---|---|
Expression |
getExpression() |
XPathContextMajor |
getSavedXPathContext() |
Item |
head()
Get the first item in the sequence.
|
SequenceIterator |
iterate()
Evaluate the expression in a given context to return an iterator over a sequence
|
static Sequence |
make(Expression expression,
XPathContext context,
int ref)
Construct a Closure by supplying the expression and the set of context variables.
|
GroundedValue |
reduce()
Reduce a value to its simplest form.
|
void |
saveContext(Expression expression,
XPathContext context) |
void |
setExpression(Expression expression) |
void |
setSavedXPathContext(XPathContextMajor savedXPathContext) |
protected Expression expression
protected XPathContextMajor savedXPathContext
protected int depth
protected SequenceIterator inputIterator
public Closure()
public static Sequence make(Expression expression, XPathContext context, int ref) throws XPathException
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 createdXPathException
- if a dynamic error occurspublic void saveContext(Expression expression, XPathContext context) throws XPathException
XPathException
public Item head() throws XPathException
head
in interface Sequence
XPathException
- in the situation where the sequence is evaluated lazily, and
evaluation of the first item causes a dynamic error.public Expression getExpression()
public XPathContextMajor getSavedXPathContext()
public void setExpression(Expression expression)
public void setSavedXPathContext(XPathContextMajor savedXPathContext)
public SequenceIterator iterate() throws XPathException
iterate
in interface Sequence
XPathException
- in the situation where the sequence is evaluated lazily, and
constructing an iterator over the items causes a dynamic error.public GroundedValue reduce() throws XPathException
XPathException
- if an error occurs doing the lazy evaluationCopyright (c) 2004-2018 Saxonica Limited. All rights reserved.