Package net.sf.saxon.expr.instruct

Class Instruction

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.instruct.Instruction

All Implemented Interfaces:

ExportAgent, TailCallReturner, Locatable, IdentityComparable, Traceable

Direct Known Subclasses:

AnalyzeString, ApplyNextMatchingTemplate, ApplyTemplates, Assign, Block, BreakInstr, CallTemplate, Choose, ComponentTracer, ConditionalBlock, CopyOf, DeepUpdate, Doctype, DoInstr, ForEach, ForEachGroup, Fork, IterateInstr, LocalParam, LocalParamBlock, MergeInstr, Message, NextIteration, ParentNodeConstructor, ResultDocument, SimpleNodeConstructor, SourceDocument, TabulateMaps, TraceExpression, UseAttributeSet, While

public abstract class Instruction
extends Expression
implements 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.

Field Summary

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

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_COST, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD

Constructor Summary

Constructors

Constructor	Description
Instruction()	Constructor

Method Summary

Modifier and Type	Method	Description
boolean	alwaysCreatesNewNodes()	Ask whether it is guaranteed that every item in the result of this instruction is a newly created node.
static ParameterSet	assembleParams(XPathContext context, WithParam[] actualParams)	Assemble a ParameterSet.
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).
protected static XPathException	dynamicError(Location 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.
java.lang.String	getExpressionName()	Get a name identifying the kind of expression, in terms meaningful to a user.
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()	Get the item type of the items returned by evaluating this instruction
int	getNetCost()	Return the estimated cost of evaluating an expression.
javax.xml.transform.SourceLocator	getSourceLocator()	Get a SourceLocator identifying the location of this instruction
boolean	isInstruction()	Ask whether this expression is an 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.
boolean	mayCreateNewNodes()	Ask whether this instruction potentially creates and returns new nodes.
abstract java.lang.Iterable<Operand>	operands()	Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.
void	process(Outputter output, XPathContext context)	Process the instruction, without returning any tail calls
abstract TailCall	processLeavingTail(Outputter output, XPathContext context)	ProcessLeavingTail: called to do the real work of this instruction.
protected boolean	someOperandCreatesNewNodes()	Helper method for mayCreateNewNodes() - returns true if any operand creates new nodes

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

addToPathMap, adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeHashCode, computeStaticProperties, copy, dynamicError, effectiveBooleanValue, equals, evaluatePendingUpdates, explain, export, getCardinality, getConfiguration, getCost, getDependencies, getEvaluationMethod, getExtraProperty, getIntegerBounds, getInterpretedExpression, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getStaticUType, getStreamerName, getTracingTag, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, markTailFunctionCalls, operandList, operandSparseList, optimize, optimizeChildren, prepareForStreaming, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, suppressValidation, toPattern, toShortString, toString, typeCheck, typeCheckChildren, typeError, unordered, verifyParentPointers

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface net.sf.saxon.trace.Traceable

gatherProperties

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.

Specified by:

getImplementationMethod in class Expression

Returns:

the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

isInstruction

public boolean isInstruction()

Description copied from class: Expression

Ask whether this expression is an instruction. In XSLT streamability analysis this is used to distinguish constructs corresponding to XSLT instructions from other constructs, typically XPath expressions (but also things like attribute constructors on a literal result element, references to attribute sets, etc. However, an XPath expression within a text value template in a text node of an XSLT stylesheet is treated as an instruction. In a non-XSLT environment (such as XQuery) this property has no meaning and its setting is undefined.

Overrides:

isInstruction in class Expression

Returns:

true if this construct originates as an XSLT instruction

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

getExpressionName

public java.lang.String getExpressionName()

Get a name identifying the kind of expression, in terms meaningful to a user.

Overrides:

getExpressionName in class Expression

Returns:

a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.

getItemType

public ItemType getItemType()

Get the item type of the items returned by evaluating this instruction

Specified by:

getItemType in class Expression

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

operands

public abstract java.lang.Iterable<Operand> operands()

Description copied from class: Expression

Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation works off the results of iterateSubExpressions()

If the expression is a Callable, then it is required that the order of the operands returned by this function is the same as the order of arguments supplied to the corresponding call() method.

Overrides:

operands in class Expression

Returns:

an iterator containing the sub-expressions of this expression

processLeavingTail

public abstract TailCall processLeavingTail(Outputter output,
                                            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:

output - the destination for the result

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 - if a dynamic error occurs during the evaluation of the instruction

process

public void process(Outputter output,
                    XPathContext context)
             throws XPathException

Process the instruction, without returning any tail calls

Overrides:

process in class Expression

Parameters:

output - the destination for the result

context - The dynamic context, giving access to the current node,

Throws:

XPathException - if a dynamic error occurs

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(Location 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

public 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 - if an error occurs evaluating one of the parameters

assembleTunnelParams

public 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 - if an error occurs evaluating one of the tunnel parameters

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

getNetCost

public int getNetCost()

Return the estimated cost of evaluating an expression. This is a very crude measure based on the syntactic form of the expression (we have no knowledge of data values). We take the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one), and we assume that a sequence has length 5. The resulting estimates may be used, for example, to reorder the predicates in a filter expression so cheaper predicates are evaluated first.

Overrides:

getNetCost in class Expression

Returns:

the intrinsic cost of this operation, excluding the costs of evaluating the operands

mayCreateNewNodes

public boolean mayCreateNewNodes()

Ask whether this instruction potentially creates and returns new nodes. Returns true if some branches or dynamic conditions result in new nodes being created. This implementation returns a default value of false

Returns:

true if the instruction creates new nodes under some input conditions (or if it can't be proved that it doesn't)

alwaysCreatesNewNodes

public boolean alwaysCreatesNewNodes()

Ask whether it is guaranteed that every item in the result of this instruction is a newly created node.

Returns:

true if result of the instruction is always either an empty sequence or a sequence consisting entirely of newly created nodes

someOperandCreatesNewNodes

protected final boolean someOperandCreatesNewNodes()

Helper method for mayCreateNewNodes() - returns true if any operand creates new nodes

Returns:

true if any operand creates new nodes

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.

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.

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?

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