Package net.sf.saxon.expr
Class LazyExpression
- java.lang.Object
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- net.sf.saxon.expr.ComputedExpression
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- net.sf.saxon.expr.UnaryExpression
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- net.sf.saxon.expr.LazyExpression
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- All Implemented Interfaces:
java.io.Serializable
,javax.xml.transform.SourceLocator
,Container
,Expression
,InstructionInfoProvider
public class LazyExpression extends UnaryExpression
A LazyExpression is an expression that forces lazy evaluation: it must not be evaluated eagerly, because a failure must not be reported unless the value is actually referenced. This is used for an expression that has been moved out of a loop. If the loop iterates zero times, the expression will not be evaluated, and in particular, it will not cause a dynamic error.- See Also:
- Serialized Form
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Field Summary
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Fields inherited from class net.sf.saxon.expr.UnaryExpression
operand
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Fields inherited from class net.sf.saxon.expr.ComputedExpression
locationId, staticProperties
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Fields inherited from interface net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description protected java.lang.String
displayOperator(Configuration config)
Give a string representation of the operator for use in diagnosticsItem
evaluateItem(XPathContext context)
Evaluate an expression as a single item.SequenceIterator
iterate(XPathContext context)
Return an Iterator to iterate over the values of a sequence.static Expression
makeLazyExpression(Expression operand)
void
process(XPathContext context)
Process the instruction, without returning any tail calls-
Methods inherited from class net.sf.saxon.expr.UnaryExpression
computeCardinality, computeSpecialProperties, display, equals, getBaseExpression, getItemType, hashCode, iterateSubExpressions, optimize, promote, replaceSubExpression, simplify, typeCheck
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Methods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, markTailFunctionCalls, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation, typeError
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Method Detail
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makeLazyExpression
public static Expression makeLazyExpression(Expression operand)
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evaluateItem
public Item evaluateItem(XPathContext context) throws XPathException
Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.- Specified by:
evaluateItem
in interfaceExpression
- Overrides:
evaluateItem
in classComputedExpression
- Parameters:
context
- The context in which the expression is to be evaluated- Returns:
- the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
- Throws:
XPathException
- if any dynamic error occurs evaluating the expression
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iterate
public SequenceIterator iterate(XPathContext context) throws XPathException
Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.- Specified by:
iterate
in interfaceExpression
- Overrides:
iterate
in classComputedExpression
- Parameters:
context
- supplies the context for evaluation- 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
public void process(XPathContext context) throws XPathException
Process the instruction, without returning any tail calls- Specified by:
process
in interfaceExpression
- Overrides:
process
in classComputedExpression
- Parameters:
context
- The dynamic context, giving access to the current node, the current variables, etc.- Throws:
XPathException
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displayOperator
protected java.lang.String displayOperator(Configuration config)
Description copied from class:UnaryExpression
Give a string representation of the operator for use in diagnostics- Specified by:
displayOperator
in classUnaryExpression
- Returns:
- the operator, as a string
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