Class Closure
- All Implemented Interfaces:
Serializable
,Expression
,ValueRepresentation
- Direct Known Subclasses:
MemoClosure
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.
- See Also:
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Field Summary
FieldsModifier and TypeFieldDescriptionprotected int
protected Expression
protected SequenceIterator
protected XPathContextMajor
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
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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 TypeMethodDescriptionvoid
display
(int level, PrintStream out, Configuration config) Diagnostic display of the expressionint
Get the cardinalityint
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().Get the static item typeint
Get the static properties of this expression (other than its type).boolean
Determine whether this Closure is indexableiterate
(XPathContext context) 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 Closure
makeIteratorClosure
(SequenceIterator 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.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
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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
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. -
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.- Throws:
XPathException
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getItemType
Get the static item type- Specified by:
getItemType
in interfaceExpression
- Overrides:
getItemType
in classValue
- Parameters:
th
-- Returns:
- for the default implementation: AnyItemType (not known)
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getCardinality
public int getCardinality()Get the cardinality- Specified by:
getCardinality
in interfaceExpression
- Overrides:
getCardinality
in classValue
- Returns:
- one of the values
StaticProperty.ALLOWS_ONE
,StaticProperty.ALLOWS_ZERO_OR_MORE
,StaticProperty.ALLOWS_ZERO_OR_ONE
,StaticProperty.ALLOWS_ONE_OR_MORE
,StaticProperty.EMPTY
. This default implementation returns ZERO_OR_MORE (which effectively gives no information).
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getSpecialProperties
public int getSpecialProperties()Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.- Specified by:
getSpecialProperties
in interfaceExpression
- Overrides:
getSpecialProperties
in classValue
- Returns:
StaticProperty.NON_CREATIVE
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getImplementationMethod
public int getImplementationMethod()An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided. This implementation provides both iterate() and process() methods natively. -
iterate
Evaluate the expression in a given context to return an iterator over a sequence- Parameters:
context
- the evaluation context. This is ignored; we use the context saved as part of the Closure instead.- Returns:
- a SequenceIterator that can be used to iterate over the result of the expression
- Throws:
XPathException
- if any dynamic error occurs evaluating the expression
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process
Process the instruction, without returning any tail calls- Specified by:
process
in interfaceExpression
- Overrides:
process
in classValue
- Parameters:
context
- The dynamic context, giving access to the current node, the current variables, etc.- Throws:
XPathException
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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
- Throws:
XPathException
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isIndexable
public boolean isIndexable()Determine whether this Closure is indexable -
display
Description copied from class:Value
Diagnostic display of the expression- Specified by:
display
in interfaceExpression
- Overrides:
display
in classValue
- Parameters:
level
- indentation level for this expressionout
- Output destinationconfig
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