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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 class net.sf.saxon.value.Value |
EMPTY_CLASS_ARRAY |
| Fields inherited from interface net.sf.saxon.expr.Expression |
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD |
| Fields inherited from interface net.sf.saxon.om.ValueRepresentation |
EMPTY_VALUE_ARRAY |
| Constructor Summary | |
Closure()
Constructor should not be called directly, instances should be made using the make() method. |
|
| Method Summary | |
void |
display(int level,
java.io.PrintStream out,
Configuration config)
Diagnostic display of the expression |
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(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. |
| Methods inherited from class net.sf.saxon.value.Value |
asItem, asIterator, asValue, checkPermittedContents, convert, convertJavaObjectToXPath, convertToJava, effectiveBooleanValue, equals, evaluateAsString, evaluateItem, getDependencies, getIterator, getLength, getParentExpression, getStringValue, getStringValueCS, hashCode, itemAt, iterateSubExpressions, makeQNameValue, optimize, promote, simplify, stringToNumber, toString, typeCheck |
| 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 |
public Closure()
| Method Detail |
public static Closure makeIteratorClosure(SequenceIterator iterator)
public static Value make(Expression expression,
XPathContext context,
int ref)
throws XPathException
XPathExceptionpublic ItemType getItemType(TypeHierarchy th)
getItemType in interface ExpressiongetItemType in class Valueth -
public int getCardinality()
getCardinality in interface ExpressiongetCardinality in class Valuepublic int getSpecialProperties()
getSpecialProperties in interface ExpressiongetSpecialProperties in class ValueStaticProperty.NON_CREATIVEpublic 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
expression
public void process(XPathContext context)
throws XPathException
process in interface Expressionprocess in class Valuecontext - The dynamic context, giving access to the current node,
the current variables, etc.
XPathException
public Value reduce()
throws XPathException
reduce in class ValueXPathExceptionpublic boolean isIndexable()
public void display(int level,
java.io.PrintStream out,
Configuration config)
Value
display in interface Expressiondisplay in class Value
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