Instruction

java.lang.Object
- net.sf.saxon.expr.Expression
- - net.sf.saxon.instruct.Instruction

All Implemented Interfaces:

java.io.Serializable, javax.xml.transform.SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, TailCallReturner, InstructionInfo, org.xml.sax.Locator

Direct Known Subclasses:

AnalyzeString, ApplyImports, ApplyTemplates, Block, BreakInstr, CallTemplate, Choose, ContinueInstr, CopyOf, Doctype, ForEach, ForEachGroup, GeneralVariable, IterateInstr, Message, ParentNodeConstructor, ResultDocument, SimpleNodeConstructor, TraceWrapper, UseAttributeSets, While
```
public abstract class Instruction
extends Expression
implements javax.xml.transform.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.

See Also:

Serialized Form

Field Summary
- Fields inherited from class net.sf.saxon.expr.Expression
  EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties

Constructor Summary

Constructors
Constructor Description

Instruction()
Constructor

Constructors
Constructor	Description
`Instruction()`	Constructor

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method	Description
`protected static ParameterSet`	`assembleParams(XPathContext context, WithParam[] actualParams)`	Assemble a ParameterSet.
`protected static ParameterSet`	`assembleTunnelParams(XPathContext context, WithParam[] actualParams)`	Assemble a ParameterSet.
`int`	`computeCardinality()`	Get the cardinality of the sequence returned by evaluating this instruction
`int`	`computeSpecialProperties()`	Get the static properties of this expression (other than its type).
`boolean`	`createsNewNodes()`	Determine whether this instruction creates new nodes.
`protected static XPathException`	`dynamicError(javax.xml.transform.SourceLocator loc, XPathException error, XPathContext context)`	Construct an exception with diagnostic information.
`java.lang.CharSequence`	`evaluateAsString(XPathContext context)`	Evaluate an expression as a String.
`Item`	`evaluateItem(XPathContext context)`	Evaluate an expression as a single item.
`int`	`getConstructType()`	Get the type of this expression for use in tracing and diagnostics
`int`	`getImplementationMethod()`	An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
`int`	`getInstructionNameCode()`	Get the namecode of the instruction for use in diagnostics
`ItemType`	`getItemType(TypeHierarchy th)`	Get the item type of the items returned by evaluating this instruction
`javax.xml.transform.SourceLocator`	`getSourceLocator()`	Get a SourceLocator identifying the location of this instruction
`boolean`	`isXSLT()`	Establish whether this is an XSLT instruction or an XQuery instruction (used to produce appropriate diagnostics)
`SequenceIterator`	`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 calls
`abstract TailCall`	`processLeavingTail(XPathContext context)`	ProcessLeavingTail: called to do the real work of this instruction.
`Expression`	`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(ExpressionVisitor visitor)`	Simplify an expression.

Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, copy, display, doPromotion, dynamicError, effectiveBooleanValue, evaluatePendingUpdates, explain, explain, findParentOf, getCardinality, getColumnNumber, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, isUpdatingExpression, iterateEvents, iterateSubExpressions, markTailFunctionCalls, optimize, replaceSubExpression, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toString, typeCheck, typeError

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface javax.xml.transform.SourceLocator
getColumnNumber, getLineNumber, getPublicId, getSystemId

- Constructor Detail
  - Instruction
```
public Instruction()
```
    Constructor
- Method Detail
  - 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.
    
    Overrides:
    
    getImplementationMethod in class Expression
    
    Returns:
    
    the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD
  - getInstructionNameCode
```
public int getInstructionNameCode()
```
    Get the namecode of the instruction for use in diagnostics
    
    Returns:
    
    a code identifying the instruction: typically but not always the fingerprint of a name in the XSLT namespace
  - getItemType
```
public ItemType getItemType(TypeHierarchy th)
```
    Get the item type of the items returned by evaluating this instruction
    
    Specified by:
    
    getItemType in class Expression
    
    Parameters:
    
    th - the type hierarchy cache
    
    Returns:
    
    the static item type of the instruction
  - computeCardinality
```
public int computeCardinality()
```
    Get the cardinality of the sequence returned by evaluating this instruction
    
    Specified by:
    
    computeCardinality in class Expression
    
    Returns:
    
    the static cardinality
  - processLeavingTail
```
public abstract TailCall processLeavingTail(XPathContext context)
                                     throws XPathException
```
    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 interface TailCallReturner
    
    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
  - process
```
public void process(XPathContext context)
             throws XPathException
```
    Process the instruction, without returning any tail calls
    
    Overrides:
    
    process in class Expression
    
    Parameters:
    
    context - The dynamic context, giving access to the current node, the current variables, etc.
    
    Throws:
    
    XPathException
  - getSourceLocator
```
public javax.xml.transform.SourceLocator getSourceLocator()
```
    Get a SourceLocator identifying the location of this instruction
    
    Returns:
    
    the location of this instruction in the source stylesheet or query
  - dynamicError
```
protected static XPathException dynamicError(javax.xml.transform.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:
    
    loc - the location of the error
    
    error - The exception containing information about the error
    
    context - The controller of the transformation
    
    Returns:
    
    an exception based on the supplied exception, but with location information added relating to this instruction
  - 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.
    
    Parameters:
    
    context - the XPath dynamic context
    
    actualParams - the set of with-param parameters that specify tunnel="no"
    
    Returns:
    
    a ParameterSet
    
    Throws:
    
    XPathException
  - 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.
    
    Parameters:
    
    context - the XPath dynamic context
    
    actualParams - the set of with-param parameters that specify tunnel="yes"
    
    Returns:
    
    a ParameterSet
    
    Throws:
    
    XPathException
  - simplify
```
public abstract Expression simplify(ExpressionVisitor visitor)
                             throws XPathException
```
    Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.
    
    Overrides:
    
    simplify in class Expression
    
    Parameters:
    
    visitor - an expression visitor
    
    Returns:
    
    the simplified expression
    
    Throws:
    
    XPathException - if an error is discovered during expression rewriting
  - 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 class Expression
    
    Returns:
    
    a set of flags indicating static properties of this expression
  - createsNewNodes
```
public boolean createsNewNodes()
```
    Determine whether this instruction creates new nodes. This implementation returns a default value of false
    
    Returns:
    
    true if the instruction creates new nodes (or if it can't be proved that it doesn't)
  - promoteInst
```
protected void promoteInst(PromotionOffer offer)
                    throws XPathException
```
    Handle promotion offers, that is, non-local tree rewrites.
    
    Parameters:
    
    offer - The type of rewrite being offered
    
    Throws:
    
    XPathException
  - promote
```
public Expression promote(PromotionOffer offer)
                   throws XPathException
```
    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.
    
    Overrides:
    
    promote in class Expression
    
    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
  - 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 interface EvaluableItem
    
    Overrides:
    
    evaluateItem in class Expression
    
    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
  - 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 interface SequenceIterable
    
    Overrides:
    
    iterate in class Expression
    
    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
  - evaluateAsString
```
public final java.lang.CharSequence evaluateAsString(XPathContext context)
                                              throws XPathException
```
    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.
    
    Overrides:
    
    evaluateAsString in class Expression
    
    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 expression
    
    java.lang.ClassCastException - if the result type of the expression is not xs:string?
  - getConstructType
```
public int getConstructType()
```
    Get the type of this expression for use in tracing and diagnostics
    
    Specified by:
    
    getConstructType in interface InstructionInfo
    
    Overrides:
    
    getConstructType in class Expression
    
    Returns:
    
    the type of expression, as enumerated in class Location
  - 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

Class Instruction

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression

Constructor Summary

Method Summary

Methods inherited from class net.sf.saxon.expr.Expression

Methods inherited from class java.lang.Object

Methods inherited from interface javax.xml.transform.SourceLocator

Constructor Detail

Instruction

Method Detail

getImplementationMethod

getInstructionNameCode

getItemType

computeCardinality

processLeavingTail

process

getSourceLocator

dynamicError

assembleParams

assembleTunnelParams

simplify

computeSpecialProperties

createsNewNodes

promoteInst

promote

evaluateItem

iterate

evaluateAsString

getConstructType

isXSLT