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java.lang.Object net.sf.saxon.value.Value<T> net.sf.saxon.value.Closure<T>
public class Closure<T extends Item>
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 | |
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protected int |
depth
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protected Expression |
expression
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protected SequenceIterator<T> |
inputIterator
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protected XPathContextMajor |
savedXPathContext
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Fields inherited from class net.sf.saxon.value.Value |
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INDETERMINATE_ORDERING |
Fields inherited from interface net.sf.saxon.om.ValueRepresentation |
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EMPTY_VALUE_ARRAY |
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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int |
getCardinality()
Get the cardinality |
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Expression |
getExpression()
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ItemType |
getItemType(TypeHierarchy th)
Get the static item type |
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XPathContextMajor |
getSavedXPathContext()
|
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SequenceIterator<T> |
iterate()
Evaluate the expression in a given context to return an iterator over a sequence |
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static Value |
make(Expression expression,
XPathContext context,
int ref)
Construct a Closure by supplying the expression and the set of context variables. |
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static
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makeIteratorClosure(SequenceIterator<T> iterator)
Construct a Closure over an existing SequenceIterator. |
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void |
process(XPathContext context)
Process the instruction, without returning any tail calls |
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Value<T> |
reduce()
Reduce a value to its simplest form. |
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void |
saveContext(Expression expression,
XPathContext context)
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void |
setExpression(Expression expression)
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void |
setSavedXPathContext(XPathContextMajor savedXPathContext)
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Methods inherited from class net.sf.saxon.value.Value |
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asItem, asItem, asIterator, asValue, checkPermittedContents, convertToJava, effectiveBooleanValue, equals, fromItem, getCanonicalLexicalRepresentation, getIterator, getLength, getSchemaComparable, getSequenceLength, getStringValue, getStringValueCS, hashCode, isIdentical, itemAt |
Methods inherited from class java.lang.Object |
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clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
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protected Expression expression
protected XPathContextMajor savedXPathContext
protected int depth
protected SequenceIterator<T extends Item> inputIterator
Constructor Detail |
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public Closure()
Method Detail |
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public static <T extends Item> ValueRepresentation<T> makeIteratorClosure(SequenceIterator<T> iterator) throws XPathException
iterator
- the supplied iterator
XPathException
- if a dynamic error occurspublic static Value 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 created
XPathException
- if a dynamic error occurspublic void saveContext(Expression expression, XPathContext context) throws XPathException
XPathException
public ItemType getItemType(TypeHierarchy th)
getItemType
in class Value<T extends Item>
th
- the type hierarchy cache
public int getCardinality()
getCardinality
in class Value<T extends Item>
public Expression getExpression()
public XPathContextMajor getSavedXPathContext()
public void setExpression(Expression expression)
public void setSavedXPathContext(XPathContextMajor savedXPathContext)
public SequenceIterator<T> iterate() throws XPathException
iterate
in class Value<T extends Item>
XPathException
- if a dynamic error occurs. This is possible only in the case of values
that are materialized lazily, that is, where the iterate() method leads to computation of an
expression that delivers the values.public void process(XPathContext context) throws XPathException
process
in class Value<T extends Item>
context
- The dynamic context, giving access to the current node,
the current variables, etc.
XPathException
- if an error occurs (for example if the value is
a closure that needs to be evaluated)public Value<T> reduce() throws XPathException
reduce
in class Value<T extends Item>
XPathException
- if an error occurs
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