Class Closure<T extends Item>
- All Implemented Interfaces:
ValueRepresentation<T>
- Direct Known Subclasses:
MemoClosure
,SingletonClosure
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.
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Field Summary
FieldsModifier and TypeFieldDescriptionprotected int
protected Expression
protected SequenceIterator<T>
protected XPathContextMajor
Fields inherited from class net.sf.saxon.value.Value
INDETERMINATE_ORDERING
Fields inherited from interface net.sf.saxon.om.ValueRepresentation
EMPTY_VALUE_ARRAY
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Constructor Summary
ConstructorsConstructorDescriptionClosure()
Constructor should not be called directly, instances should be made using the make() method. -
Method Summary
Modifier and TypeMethodDescriptionint
Get the cardinalityGet the static item typeiterate()
Evaluate the expression in a given context to return an iterator over a sequencestatic Value
make
(Expression expression, XPathContext context, int ref) Construct a Closure by supplying the expression and the set of context variables.static <T extends Item>
ValueRepresentation<T>makeIteratorClosure
(SequenceIterator<T> iterator) Construct a Closure over an existing SequenceIterator.void
process
(XPathContext context) Process the instruction, without returning any tail callsreduce()
Reduce a value to its simplest form.void
saveContext
(Expression expression, XPathContext context) void
setExpression
(Expression expression) void
setSavedXPathContext
(XPathContextMajor savedXPathContext) Methods inherited from class net.sf.saxon.value.Value
asItem, asItem, asIterator, asValue, checkPermittedContents, convertToJava, effectiveBooleanValue, equals, fromItem, getCanonicalLexicalRepresentation, getIterator, getLength, getSchemaComparable, getSequenceLength, getStringValue, getStringValueCS, hashCode, isIdentical, itemAt
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Field Details
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expression
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savedXPathContext
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depth
protected int depth -
inputIterator
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Constructor Details
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Closure
public Closure()Constructor should not be called directly, instances should be made using the make() method.
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Method Details
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makeIteratorClosure
public static <T extends Item> ValueRepresentation<T> makeIteratorClosure(SequenceIterator<T> iterator) throws XPathException Construct a Closure over an existing SequenceIterator. This is used when an extension function returns a SequenceIterator as its result (it replaces the old SequenceIntent class for this purpose). There is no known expression in this case. Note that the caller must ensure this is a "clean" iterator: it must be positioned at the start, and must not be shared by anyone else.- Parameters:
iterator
- the supplied iterator- Returns:
- the Closure over this iterator
- Throws:
XPathException
- if a dynamic error occurs
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make
public static Value make(Expression expression, XPathContext context, int ref) throws XPathException Construct a Closure by supplying the expression and the set of context variables.- Parameters:
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- Returns:
- the Closure, a virtual value that can later be materialized when its content is required
- Throws:
XPathException
- if a dynamic error occurs
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saveContext
- Throws:
XPathException
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getItemType
Get the static item type- Overrides:
getItemType
in classValue<T extends Item>
- Parameters:
th
- the type hierarchy cache- Returns:
- for the default implementation: AnyItemType (not known)
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getCardinality
public int getCardinality()Get the cardinality- Overrides:
getCardinality
in classValue<T extends Item>
- Returns:
- the cardinality
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getExpression
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getSavedXPathContext
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setExpression
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setSavedXPathContext
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iterate
Evaluate the expression in a given context to return an iterator over a sequence- Specified by:
iterate
in classValue<T extends Item>
- Returns:
- an iterator over the sequence of items
- Throws:
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.
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process
Process the instruction, without returning any tail calls- Overrides:
process
in classValue<T extends Item>
- Parameters:
context
- The dynamic context, giving access to the current node, the current variables, etc.- Throws:
XPathException
- if an error occurs (for example if the value is a closure that needs to be evaluated)
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reduce
Reduce a value to its simplest form. If the value is a closure or some other form of deferred value such as a FunctionCallPackage, then it is reduced to a SequenceExtent. If it is a SequenceExtent containing a single item, then it is reduced to that item. One consequence that is exploited by class FilterExpression is that if the value is a singleton numeric value, then the result will be an instance of NumericValue- Overrides:
reduce
in classValue<T extends Item>
- Returns:
- the value in simplified form
- Throws:
XPathException
- if an error occurs
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