Package net.sf.saxon.value
Class SingletonClosure
java.lang.Object
net.sf.saxon.value.Value
net.sf.saxon.value.Closure
net.sf.saxon.value.SingletonClosure
- All Implemented Interfaces:
ValueRepresentation
A SingletonClosure 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. The value of a SingletonClosure is always either a single item
or an empty sequence.
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
Fields inherited from class net.sf.saxon.value.Closure
depth, expression, inputIterator, savedXPathContext
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
ConstructorsConstructorDescriptionSingletonClosure
(Expression exp, XPathContext context) Constructor should not be called directly, instances should be made using the make() method. -
Method Summary
Modifier and TypeMethodDescriptionasItem()
Return the value in the form of an Itemint
Get the length of the sequenceitemAt
(int n) Get the n'th item in the sequence (starting from 0).iterate()
Evaluate the expression in a given context to return an iterator over a sequenceReturn a value containing all the items in the sequence returned by this SequenceIteratorvoid
process
(XPathContext context) Process the expression by writing the value to the current ReceiverMethods inherited from class net.sf.saxon.value.Closure
getCardinality, getExpression, getItemType, getSavedXPathContext, make, makeIteratorClosure, reduce, saveContext, setExpression, setSavedXPathContext
Methods inherited from class net.sf.saxon.value.Value
asItem, asIterator, asValue, checkPermittedContents, convertToJava, effectiveBooleanValue, equals, fromItem, getCanonicalLexicalRepresentation, getIterator, getSchemaComparable, getSequenceLength, getStringValue, getStringValueCS, hashCode, isIdentical
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Constructor Details
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SingletonClosure
Constructor should not be called directly, instances should be made using the make() method.- Parameters:
exp
- the expression to be lazily evaluatedcontext
- the context in which the expression should be evaluated- Throws:
XPathException
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Method Details
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iterate
Evaluate the expression in a given context to return an iterator over a sequence- Overrides:
iterate
in classClosure
- 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 expression by writing the value to the current Receiver- Overrides:
process
in classClosure
- 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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asItem
Return the value in the form of an Item- Overrides:
asItem
in classValue
- Returns:
- the value in the form of an Item
- Throws:
XPathException
- if an error occurs, notably if this value is a sequence containing more than one item
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itemAt
Get the n'th item in the sequence (starting from 0). This is defined for all SequenceValues, but its real benefits come for a SequenceValue stored extensionally- Overrides:
itemAt
in classValue
- Parameters:
n
- position of the required item, counting from zero.- Returns:
- the n'th item in the sequence, where the first item in the sequence is numbered zero. If n is negative or >= the length of the sequence, returns null.
- Throws:
XPathException
- if an error occurs (for example if the value is a Closure that needs to be evaluated to find the Nth item)
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getLength
Get the length of the sequence- Overrides:
getLength
in classValue
- Returns:
- the number of items in the sequence
- Throws:
XPathException
- if an error occurs (for example if the value is a closure that needs to be read to determine its length)
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materialize
Return a value containing all the items in the sequence returned by this SequenceIterator- Returns:
- the corresponding value
- Throws:
XPathException
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