net.sf.saxon.expr.instruct

Class ForEach

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.instruct.Instruction

net.sf.saxon.expr.instruct.ForEach

All Implemented Interfaces:

ContextMappingFunction<Item<?>>, ContextOriginator, ContextSwitchingExpression, ExportAgent, TailCallReturner, Locatable, IdentityComparable

Direct Known Subclasses:

MultithreadedForEach

public class ForEach
extends Instruction
implements ContextMappingFunction<Item<?>>, ContextSwitchingExpression

Handler for xsl:for-each elements in a stylesheet. The same class handles the "!" operator in XPath 3.0, which has identical semantics to xsl:for-each, and it is used to support the "/" operator in cases where it is known that the rhs delivers atomic values.

Field Summary

Fields

Modifier and Type	Field and Description
protected Operand	actionOp
protected boolean	containsTailCall
protected boolean	isInstruction
protected Operand	selectOp
protected Operand	threadsOp

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 and Description
ForEach(Expression select, Expression action) Create an xsl:for-each instruction
ForEach(Expression select, Expression action, boolean containsTailCall, Expression threads) Create an xsl:for-each instruction

Method Summary

Modifier and Type	Method and Description
PathMap.PathMapNodeSet	addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet) Add a representation of this expression to a PathMap.
boolean	alwaysCreatesNewNodes() Ask whether it is guaranteed that every item in the result of this instruction is a newly created node.
void	checkForUpdatingSubexpressions() Check to ensure that this expression does not contain any inappropriate updating subexpressions.
void	checkPermittedContents(SchemaType parentType, boolean whole) Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type.
int	computeSpecialProperties() Get the static properties of this expression (other than its type).
Expression	copy(RebindingMap rebindings) Copy an expression.
void	evaluatePendingUpdates(XPathContext context, PendingUpdateList pul) Evaluate an updating expression, adding the results to a Pending Update List.
protected void	explainThreads(ExpressionPresenter out)
void	export(ExpressionPresenter out) Diagnostic print of expression structure.
Expression	getAction() Get the action expression (in XSLT, the body of the xsl:for-each instruction
Expression	getActionExpression() Get the subexpression that is evaluated in the new context
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 name of this instruction for diagnostic and tracing purposes
ItemType	getItemType() Determine the data type of the items returned by this expression
Expression	getNumberOfThreadsExpression() Get the number of threads requested
Expression	getSelect() Get the select expression
Expression	getSelectExpression() Get the select expression
UType	getStaticUType(UType contextItemType) Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.
java.lang.String	getStreamerName() Get the (partial) name of a class that supports streaming of this kind of expression
Expression	getThreads() Get the expression used to determine how many threads to use when multi-threading
boolean	isInstruction() Ask whether this expression is an instruction.
boolean	isUpdatingExpression() Determine whether this is an updating expression as defined in the XQuery update specification
SequenceIterator<?>	iterate(XPathContext context) Return an Iterator to iterate over the values of the sequence.
SequenceIterator<?>	map(XPathContext context) Map one item to a sequence.
boolean	mayCreateNewNodes() Determine whether this instruction creates new nodes.
java.lang.Iterable<Operand>	operands() Get the operands of this expression
Expression	optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Perform optimisation of an expression and its subexpressions.
TailCall	processLeavingTail(XPathContext context) ProcessLeavingTail: called to do the real work of this instruction.
void	setAction(Expression action) Set the action expression (in XSLT, the body of the xsl:for-each instruction)
void	setActionExpression(Expression action) Set the action expression
void	setInstruction(boolean inst) Say whether this ForEach expression originates as an XSLT instruction
void	setSelect(Expression select) Set the select expression
void	setSelectExpression(Expression select) Set the select expression
void	setThreads(Expression threads) Set the expression used to determine how many threads to use when multi-threading
java.lang.String	toShortString() Produce a short string identifying the expression for use in error messages
java.lang.String	toString() The toString() method for an expression attempts to give a representation of the expression in an XPath-like form.
Expression	typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Perform type checking of an expression and its subexpressions.
Expression	unordered(boolean retainAllNodes, boolean forStreaming) Replace this expression by a simpler expression that delivers the results without regard to order.

Methods inherited from class net.sf.saxon.expr.instruct.Instruction

assembleParams, assembleTunnelParams, computeCardinality, dynamicError, evaluateAsString, evaluateItem, getConstructType, getNetCost, getSourceLocator, isXSLT, process, someOperandCreatesNewNodes

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

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

Methods inherited from class java.lang.Object

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

Field Detail

containsTailCall

protected boolean containsTailCall

selectOp

protected Operand selectOp

actionOp

protected Operand actionOp

threadsOp

protected Operand threadsOp

isInstruction

protected boolean isInstruction

Constructor Detail

ForEach

public ForEach(Expression select,
               Expression action)

Create an xsl:for-each instruction

Parameters:

select - the select expression

action - the body of the xsl:for-each loop

ForEach

public ForEach(Expression select,
               Expression action,
               boolean containsTailCall,
               Expression threads)

Create an xsl:for-each instruction

Parameters:

select - the select expression

action - the body of the xsl:for-each loop

containsTailCall - true if the body of the loop contains a tail call on the containing function

threads - if >1 causes multithreaded execution (Saxon-EE only)

Method Detail

setInstruction

public void setInstruction(boolean inst)

Say whether this ForEach expression originates as an XSLT instruction

Parameters:

inst - true if this is an xsl:for-each instruction; false if it is the XPath "!" operator

isInstruction

public boolean isInstruction()

Ask whether this expression is an instruction. In XSLT streamability analysis this is used to distinguish constructs corresponding to XSLT instructions from other constructs.

Overrides:

isInstruction in class Instruction

Returns:

true if this construct originates as an XSLT instruction

getSelect

public Expression getSelect()

Get the select expression

Returns:

the select expression. Note this will have been wrapped in a sort expression if sorting was requested.

setSelect

public void setSelect(Expression select)

Set the select expression

Parameters:

select - the select expression of the for-each

getAction

public Expression getAction()

Get the action expression (in XSLT, the body of the xsl:for-each instruction

Returns:

the action expression

setAction

public void setAction(Expression action)

Set the action expression (in XSLT, the body of the xsl:for-each instruction)

Parameters:

action - the action expression

getThreads

public Expression getThreads()

Get the expression used to determine how many threads to use when multi-threading

Returns:

the saxon:threads expression if present, or null otherwise

setThreads

public void setThreads(Expression threads)

Set the expression used to determine how many threads to use when multi-threading

Parameters:

threads - the saxon:threads expression if present, or null otherwise

operands

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

Get the operands of this expression

Specified by:

operands in class Instruction

Returns:

the operands

getInstructionNameCode

public int getInstructionNameCode()

Get the name of this instruction for diagnostic and tracing purposes

Overrides:

getInstructionNameCode in class Instruction

Returns:

the code for name xsl:for-each

getSelectExpression

public Expression getSelectExpression()

Get the select expression

Specified by:

getSelectExpression in interface ContextSwitchingExpression

Returns:

the select expression. Note this will have been wrapped in a sort expression if sorting was requested.

setSelectExpression

public void setSelectExpression(Expression select)

Set the select expression

Parameters:

select - the select expression

setActionExpression

public void setActionExpression(Expression action)

Set the action expression

Parameters:

action - the select expression

getActionExpression

public Expression getActionExpression()

Get the subexpression that is evaluated in the new context

Specified by:

getActionExpression in interface ContextSwitchingExpression

Returns:

the subexpression evaluated in the context set by the controlling expression

getNumberOfThreadsExpression

public Expression getNumberOfThreadsExpression()

Get the number of threads requested

Returns:

the value of the saxon:threads attribute

getItemType

public final ItemType getItemType()

Determine the data type of the items returned by this expression

Overrides:

getItemType in class Instruction

Returns:

the data type

getStaticUType

public UType getStaticUType(UType contextItemType)

Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.

Overrides:

getStaticUType in class Expression

Parameters:

contextItemType - static type of the context item

Returns:

the static item type of the expression according to the XSLT 3.0 defined rules

mayCreateNewNodes

public final boolean mayCreateNewNodes()

Determine whether this instruction creates new nodes. This implementation returns true if the "action" creates new nodes. (Nodes created by the condition can't contribute to the result).

Overrides:

mayCreateNewNodes in class Instruction

Returns:

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

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ContextItemStaticInfo contextInfo)
                     throws XPathException

Description copied from class: Expression

Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.

Overrides:

typeCheck in class Expression

Parameters:

visitor - an expression visitor

contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.

Returns:

the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations

Throws:

XPathException - if an error is discovered during this phase (typically a type error)

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ContextItemStaticInfo contextInfo)
                    throws XPathException

Description copied from class: Expression

Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

Overrides:

optimize in class Expression

Parameters:

visitor - an expression visitor

contextInfo - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE

Returns:

the original expression, rewritten if appropriate to optimize execution

Throws:

XPathException - if an error is discovered during this phase (typically a type error)

unordered

public Expression unordered(boolean retainAllNodes,
                            boolean forStreaming)
                     throws XPathException

Replace this expression by a simpler expression that delivers the results without regard to order.

Overrides:

unordered in class Expression

Parameters:

retainAllNodes - set to true if the result must contain exactly the same nodes as the original; set to false if the result can eliminate (or introduce) duplicates.

forStreaming - set to true if optimizing for streaming

Returns:

an expression that delivers the same nodes in a more convenient order

Throws:

XPathException - if the rewrite fails

addToPathMap

public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap,
                                           PathMap.PathMapNodeSet pathMapNodeSet)

Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.

The default implementation of this method assumes that an expression does no navigation other than the navigation done by evaluating its subexpressions, and that the subexpressions are evaluated in the same context as the containing expression. The method must be overridden for any expression where these assumptions do not hold. For example, implementations exist for AxisExpression, ParentExpression, and RootExpression (because they perform navigation), and for the doc(), document(), and collection() functions because they create a new navigation root. Implementations also exist for PathExpression and FilterExpression because they have subexpressions that are evaluated in a different context from the calling expression.

Overrides:

addToPathMap in class Expression

Parameters:

pathMap - the PathMap to which the expression should be added

pathMapNodeSet - the set of nodes in the path map that are affected

Returns:

the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression. For an expression that does navigation, it represents the end of the arc in the path map that describes the navigation route. For other expressions, it is the same as the input pathMapNode.

copy

public Expression copy(RebindingMap rebindings)

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Parameters:

rebindings - variables that need to be re-bound

Returns:

the copy of the original expression

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 Instruction

Returns:

a set of flags indicating static properties of this expression

alwaysCreatesNewNodes

public boolean alwaysCreatesNewNodes()

Description copied from class: Instruction

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

Overrides:

alwaysCreatesNewNodes in class Instruction

Returns:

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

isUpdatingExpression

public boolean isUpdatingExpression()

Determine whether this is an updating expression as defined in the XQuery update specification

Overrides:

isUpdatingExpression in class Expression

Returns:

true if this is an updating expression

checkForUpdatingSubexpressions

public void checkForUpdatingSubexpressions()
                                    throws XPathException

Check to ensure that this expression does not contain any inappropriate updating subexpressions. This check is overridden for those expressions that permit updating subexpressions.

Overrides:

checkForUpdatingSubexpressions in class Expression

Throws:

XPathException - if the expression has a non-permitted updating subexpression

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.

Overrides:

getImplementationMethod in class Instruction

Returns:

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

checkPermittedContents

public void checkPermittedContents(SchemaType parentType,
                                   boolean whole)
                            throws XPathException

Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type. It's always OK to say yes, since the check will be repeated at run-time. The process of checking element and attribute constructors against the content model of a complex type also registers the type of content expected of those constructors, so the static validation can continue recursively.

Overrides:

checkPermittedContents in class Expression

Parameters:

parentType - the "given complex type": the method is checking that the nodes returned by this expression are acceptable members of the content model of this type

whole - if true, we want to check that the value of this expression satisfies the content model as a whole; if false we want to check that the value of the expression is acceptable as one part of the content

Throws:

XPathException - if the value delivered by this expression cannot be part of the content model of the given type

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
                            throws XPathException

Description copied from class: Instruction

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

Specified by:

processLeavingTail in class Instruction

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

iterate

public SequenceIterator<?> iterate(XPathContext context)
                            throws XPathException

Return an Iterator to iterate over the values of the sequence.

Overrides:

iterate in class Instruction

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

map

public SequenceIterator<?> map(XPathContext context)
                        throws XPathException

Map one item to a sequence.

Specified by:

map in interface ContextMappingFunction<Item<?>>

Parameters:

context - The processing context. The item to be mapped is the context item identified from this context: the values of position() and last() also relate to the set of items being mapped

Returns:

a SequenceIterator over the sequence of items that the supplied input item maps to

Throws:

XPathException - if a dynamic error is detected

evaluatePendingUpdates

public void evaluatePendingUpdates(XPathContext context,
                                   PendingUpdateList pul)
                            throws XPathException

Evaluate an updating expression, adding the results to a Pending Update List. The default implementation of this method, which is used for non-updating expressions, throws an UnsupportedOperationException

Overrides:

evaluatePendingUpdates in class Expression

Parameters:

context - the XPath dynamic evaluation context

pul - the pending update list to which the results should be written

Throws:

XPathException - if evaluation fails

java.lang.UnsupportedOperationException - if the expression is not an updating expression

export

public void export(ExpressionPresenter out)
            throws XPathException

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

export in interface ExportAgent

Specified by:

export in class Expression

Parameters:

out - the expression presenter used to display the structure

Throws:

XPathException - if the export fails, for example if an expression is found that won't work in the target environment.

explainThreads

protected void explainThreads(ExpressionPresenter out)
                       throws XPathException

Throws:

XPathException

toString

public java.lang.String toString()

The toString() method for an expression attempts to give a representation of the expression in an XPath-like form.

For subclasses of Expression that represent XPath expressions, the result should always be a string that parses as an XPath 3.0 expression

Overrides:

toString in class Expression

Returns:

a representation of the expression as a string

toShortString

public java.lang.String toShortString()

Description copied from class: Expression

Produce a short string identifying the expression for use in error messages

Overrides:

toShortString in class Expression

Returns:

a short string, sufficient to identify the expression

getExpressionName

public java.lang.String getExpressionName()

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

Overrides:

getExpressionName in class Instruction

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.

getStreamerName

public java.lang.String getStreamerName()

Get the (partial) name of a class that supports streaming of this kind of expression

Overrides:

getStreamerName in class Expression

Returns:

the partial name of a class that can be instantiated to provide streaming support in Saxon-EE, or null if there is no such class