Package net.sf.saxon.instruct
Class Instruction
java.lang.Object
net.sf.saxon.expr.ComputedExpression
net.sf.saxon.instruct.Instruction
- All Implemented Interfaces:
Serializable
,SourceLocator
,Container
,Expression
,TailCallReturner
,InstructionInfoProvider
- Direct Known Subclasses:
AnalyzeString
,ApplyImports
,ApplyTemplates
,Block
,CallTemplate
,Choose
,CopyOf
,Doctype
,ForEach
,ForEachGroup
,GeneralVariable
,Message
,ParentNodeConstructor
,ResultDocument
,SimpleNodeConstructor
,TraceWrapper
,UseAttributeSets
,While
public abstract class Instruction
extends ComputedExpression
implements SourceLocator, TailCallReturner
Abstract superclass for all instructions in the compiled stylesheet.
This represents a compiled instruction, and as such, the minimum information is
retained from the original stylesheet.
Note: this class implements SourceLocator: that is, it can identify where in the stylesheet the source instruction was located.
Note: this class implements SourceLocator: that is, it can identify where in the stylesheet the source instruction was located.
- See Also:
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Field Summary
Fields inherited from class net.sf.saxon.expr.ComputedExpression
locationId, staticProperties
Fields inherited from interface net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionstatic void
appendItem
(Item it, SequenceReceiver out, int locationId) Static method to append an item that results from evaluating an expression to the current result receiver.protected static ParameterSet
assembleParams
(XPathContext context, WithParam[] actualParams) Assemble a ParameterSet.protected static ParameterSet
assembleTunnelParams
(XPathContext context, WithParam[] actualParams) Assemble a ParameterSet.int
Get the cardinality of the sequence returned by evaluating this instructionint
Get the static properties of this expression (other than its type).boolean
Determine whether this instruction creates new nodes.protected static XPathException
dynamicError
(SourceLocator loc, XPathException error, XPathContext context) Construct an exception with diagnostic information.final String
evaluateAsString
(XPathContext context) Evaluate an expression as a String.evaluateItem
(XPathContext context) Evaluate an expression as a single item.int
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().Get InstructionInfo for this expressionint
Get the namecode of the instruction for use in diagnosticsGet the item type of the items returned by evaluating this instructionGet a SourceLocator identifying the location of this instructionboolean
isXSLT()
Establish whether this is an XSLT instruction or an XQuery instruction (used to produce appropriate diagnostics)iterate
(XPathContext context) Return an Iterator to iterate over the values of a sequence.void
process
(XPathContext context) Process the instruction, without returning any tail callsabstract TailCall
processLeavingTail
(XPathContext context) ProcessLeavingTail: called to do the real work of this instruction.promote
(PromotionOffer offer) Offer promotion for this subexpression.protected void
promoteInst
(PromotionOffer offer) Handle promotion offers, that is, non-local tree rewrites.abstract Expression
simplify
(StaticContext env) Simplify an expression.Methods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterateSubExpressions, markTailFunctionCalls, replaceSubExpression, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation, typeError
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Methods inherited from interface net.sf.saxon.expr.Expression
display, optimize, typeCheck
Methods inherited from interface javax.xml.transform.SourceLocator
getColumnNumber, getLineNumber, getPublicId, getSystemId
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Constructor Details
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Instruction
public Instruction()Constructor
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Method Details
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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 prefered. For instructions this is the process() method.- Specified by:
getImplementationMethod
in interfaceExpression
- Overrides:
getImplementationMethod
in classComputedExpression
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getInstructionNameCode
public int getInstructionNameCode()Get the namecode of the instruction for use in diagnostics -
getItemType
Get the item type of the items returned by evaluating this instruction- Specified by:
getItemType
in interfaceExpression
- Parameters:
th
-- Returns:
- the static item type of the instruction
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computeCardinality
public int computeCardinality()Get the cardinality of the sequence returned by evaluating this instruction- Specified by:
computeCardinality
in classComputedExpression
- Returns:
- the static cardinality
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processLeavingTail
ProcessLeavingTail: called to do the real work of this instruction. This method must be implemented in each subclass. The results of the instruction are written to the current Receiver, which can be obtained via the Controller.- Specified by:
processLeavingTail
in interfaceTailCallReturner
- Parameters:
context
- The dynamic context of the transformation, giving access to the current node, the current variables, etc.- Returns:
- null if the instruction has completed execution; or a TailCall indicating a function call or template call that is delegated to the caller, to be made after the stack has been unwound so as to save stack space.
- Throws:
XPathException
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process
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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getSourceLocator
Get a SourceLocator identifying the location of this instruction -
dynamicError
protected static XPathException dynamicError(SourceLocator loc, XPathException error, XPathContext context) Construct an exception with diagnostic information. Note that this method returns the exception, it does not throw it: that is up to the caller.- Parameters:
error
- The exception containing information about the errorcontext
- The controller of the transformation- Returns:
- an exception based on the supplied exception, but with location information added relating to this instruction
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assembleParams
protected static ParameterSet assembleParams(XPathContext context, WithParam[] actualParams) throws XPathException Assemble a ParameterSet. Method used by instructions that have xsl:with-param children. This method is used for the non-tunnel parameters.- Throws:
XPathException
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assembleTunnelParams
protected static ParameterSet assembleTunnelParams(XPathContext context, WithParam[] actualParams) throws XPathException Assemble a ParameterSet. Method used by instructions that have xsl:with-param children. This method is used for the tunnel parameters.- Throws:
XPathException
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simplify
Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.- Specified by:
simplify
in interfaceExpression
- Overrides:
simplify
in classComputedExpression
- Parameters:
env
- the static context- Returns:
- the simplified expression
- Throws:
XPathException
- if an error is discovered during expression rewriting
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computeSpecialProperties
public int computeSpecialProperties()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.- Overrides:
computeSpecialProperties
in classComputedExpression
- Returns:
- a set of flags indicating static properties of this expression
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createsNewNodes
public boolean createsNewNodes()Determine whether this instruction creates new nodes. This implementation returns a default value of false -
promoteInst
Handle promotion offers, that is, non-local tree rewrites.- Parameters:
offer
- The type of rewrite being offered- Throws:
XPathException
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promote
Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. This method is always called at compile time.- Specified by:
promote
in interfaceExpression
- Overrides:
promote
in classComputedExpression
- Parameters:
offer
- details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression- Returns:
- if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
- Throws:
XPathException
- if any error is detected
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evaluateItem
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
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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evaluateAsString
Evaluate an expression as a String. This function must only be called in contexts where it is known that the expression will return a single string (or where an empty sequence is to be treated as a zero-length string). Implementations should not attempt to convert the result to a string, other than converting () to "". This method is used mainly to evaluate expressions produced by compiling an attribute value template.- Specified by:
evaluateAsString
in interfaceExpression
- Overrides:
evaluateAsString
in classComputedExpression
- Parameters:
context
- The context in which the expression is to be evaluated- Returns:
- the value of the expression, evaluated in the current context. The expression must return a string or (); if the value of the expression is (), this method returns "".
- Throws:
XPathException
- if any dynamic error occurs evaluating the expressionClassCastException
- if the result type of the expression is not xs:string?
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getInstructionInfo
Description copied from class:ComputedExpression
Get InstructionInfo for this expression- Specified by:
getInstructionInfo
in interfaceInstructionInfoProvider
- Overrides:
getInstructionInfo
in classComputedExpression
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appendItem
Static method to append an item that results from evaluating an expression to the current result receiver. The method checks to see whether the item returned from the expression is actually a function-call-package representing the result of a tail call optimization; if so, the tail function calls are complete and the final result is passed on.- Parameters:
it
- the item: possibly a FunctionCallPackageout
- the Receiver- Throws:
XPathException
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isXSLT
public boolean isXSLT()Establish whether this is an XSLT instruction or an XQuery instruction (used to produce appropriate diagnostics)- Returns:
- true for XSLT, false for XQuery
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