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java.lang.Objectnet.sf.saxon.value.Value
net.sf.saxon.value.Closure
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.
Field Summary | |
protected int |
depth
|
protected Expression |
expression
|
protected SequenceIterator |
inputIterator
|
protected XPathContextMajor |
savedXPathContext
|
Fields inherited from interface net.sf.saxon.expr.Expression |
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD |
Constructor Summary | |
protected |
Closure()
Private constructor: instances must be created using the make() method |
Method Summary | |
void |
display(int level,
NamePool pool,
java.io.PrintStream out)
Convert to Java object (for passing to external functions) |
int |
getCardinality()
Get the cardinality |
int |
getImplementationMethod()
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). |
ItemType |
getItemType()
Get the static item type |
int |
getSpecialProperties()
Get the static properties of this expression (other than its type). |
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,
boolean save)
Construct a Closure by supplying the expression and the set of context variables. |
void |
process(XPathContext context)
Process the instruction, without returning any tail calls |
Methods inherited from class net.sf.saxon.value.Value |
analyze, asItem, asValue, checkPermittedContents, collapseWhitespace, convert, convertJavaObjectToXPath, convertToJava, effectiveBooleanValue, equals, evaluateAsString, evaluateItem, getDependencies, getIterator, getLength, getParentExpression, getStringValue, hashCode, itemAt, iterateSubExpressions, makeQNameValue, normalizeWhitespace, promote, simplify, stringToNumber, toString, trimWhitespace |
Methods inherited from class java.lang.Object |
clone, finalize, getClass, notify, notifyAll, wait, wait, wait |
Field Detail |
protected Expression expression
protected XPathContextMajor savedXPathContext
protected int depth
protected SequenceIterator inputIterator
Constructor Detail |
protected Closure()
Method Detail |
public static Value make(Expression expression, XPathContext context, boolean save) throws XPathException
XPathException
public ItemType getItemType()
getItemType
in interface Expression
getItemType
in class Value
public int getCardinality()
getCardinality
in interface Expression
getCardinality
in class Value
public int getSpecialProperties()
getSpecialProperties
in interface Expression
getSpecialProperties
in class Value
StaticProperty.NON_CREATIVE
public int getImplementationMethod()
public SequenceIterator iterate(XPathContext context) throws XPathException
context
- the evaluation context. This is ignored; we use the context saved
as part of the Closure instead.
XPathException
- if any dynamic error occurs evaluating the
expressionpublic void process(XPathContext context) throws XPathException
process
in interface Expression
process
in class Value
context
- The dynamic context, giving access to the current node,
the current variables, etc.
XPathException
public void display(int level, NamePool pool, java.io.PrintStream out)
display
in interface Expression
display
in class Value
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