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:

Serializable, SourceLocator, LocationProvider, SaxonLocator, ContextMappingFunction, EvaluableItem, TailCallReturner, SequenceIterable, InstructionInfo, Locator

Direct Known Subclasses:

MultithreadedForEach

public class ForEach
extends Instruction
implements ContextMappingFunction

Handler for xsl:for-each elements in a stylesheet.

See Also:

Serialized Form

Field Summary

protected Expression	action
protected boolean	containsTailCall
protected Expression	select
protected int	threads

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

EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, PUSH_SELECTION, staticProperties, WATCH_METHOD

Constructor Summary

ForEach()
Base constructor to allow subclassing

ForEach(Expression select, Expression action)
Create an xsl:for-each instruction

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

Method Summary

PathMap.PathMapNodeSet	addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet) Add a representation of this expression to a PathMap.
void	checkPermittedContents(SchemaType parentType, StaticContext env, 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	computeDependencies() Compute the dependencies of an expression, as the union of the dependencies of its subexpressions.
Expression	copy() Copy an expression.
boolean	createsNewNodes() Determine whether this instruction creates new nodes.
void	explain(ExpressionPresenter out) Diagnostic print of expression structure.
protected void	explainThreads(ExpressionPresenter out)
Expression	getActionExpression() Get the action expression (the content of the for-each)
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(TypeHierarchy th) Determine the data type of the items returned by this expression
int	getNumberOfThreads() Get the number of threads requested
Expression	getSelectExpression() Get the select expression
boolean	hasLoopingSubexpression(Expression child) Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
SequenceIterator	iterate(XPathContext context) Return an Iterator to iterate over the values of the sequence.
Iterator<Expression>	iterateSameFocusSubExpressions() Get the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression.
Iterator<Expression>	iterateSubExpressions() Get all the XPath expressions associated with this instruction (in XSLT terms, the expression present on attributes of the instruction, as distinct from the child instructions in a sequence construction)
SequenceIterator	map(XPathContext context) Map one item to a sequence.
Expression	optimize(ExpressionVisitor visitor, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
TailCall	processLeavingTail(XPathContext context) ProcessLeavingTail: called to do the real work of this instruction.
protected void	promoteInst(PromotionOffer offer) Handle promotion offers, that is, non-local tree rewrites.
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
Expression	simplify(ExpressionVisitor visitor) Simplify an expression.
Expression	typeCheck(ExpressionVisitor visitor, ItemType contextItemType) Perform type checking of an expression and its subexpressions.

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

assembleParams, assembleTunnelParams, computeCardinality, computeSpecialProperties, dynamicError, evaluateAsString, evaluateItem, getConstructType, getExpressionName, getInstructionName, getIteratorFromProcessMethod, getSourceLocator, isXSLT, process, promote

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

adoptChildExpression, checkForUpdatingSubexpressions, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getContainer, getDependencies, getEvaluationMethod, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateEvents, markTailFunctionCalls, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toString, 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

Field Detail

select

protected Expression select

action

protected Expression action

threads

protected int threads

containsTailCall

protected boolean containsTailCall

Constructor Detail

ForEach

public ForEach()

Base constructor to allow subclassing

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,
               int 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

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

Returns:

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

getActionExpression

public Expression getActionExpression()

Get the action expression (the content of the for-each)

Returns:

the body of the for-each loop

getNumberOfThreads

public int getNumberOfThreads()

Get the number of threads requested

Returns:

the value of the saxon:threads attribute

getItemType

public final ItemType getItemType(TypeHierarchy th)

Determine the data type of the items returned by this expression

Overrides:

getItemType in class Instruction

Parameters:

th - the type hierarchy cache

Returns:

the data type

createsNewNodes

public final boolean createsNewNodes()

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:

createsNewNodes in class Instruction

Returns:

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

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException

Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression).

Specified by:

simplify in class Instruction

Parameters:

visitor - the expression visitor

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
                     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.

If the implementation returns a value other than "this", then it is required to ensure that the location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.

Overrides:

typeCheck in class Expression

Parameters:

visitor - an expression visitor

contextItemType - 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 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,
                           ItemType contextItemType)
                    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

contextItemType - 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)

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()

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Returns:

the copy of the original expression

computeDependencies

public int computeDependencies()

Compute the dependencies of an expression, as the union of the dependencies of its subexpressions. (This is overridden for path expressions and filter expressions, where the dependencies of a subexpression are not all propogated). This method should be called only once, to compute the dependencies; after that, getDependencies should be used.

Overrides:

computeDependencies in class Expression

Returns:

the depencies, as a bit-mask

promoteInst

protected void promoteInst(PromotionOffer offer)
                    throws XPathException

Handle promotion offers, that is, non-local tree rewrites.

Overrides:

promoteInst in class Instruction

Parameters:

offer - The type of rewrite being offered

Throws:

XPathException

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()

Get all the XPath expressions associated with this instruction (in XSLT terms, the expression present on attributes of the instruction, as distinct from the child instructions in a sequence construction)

Overrides:

iterateSubExpressions in class Expression

Returns:

an iterator containing the sub-expressions of this expression

iterateSameFocusSubExpressions

public Iterator<Expression> iterateSameFocusSubExpressions()

Get the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression.

Overrides:

iterateSameFocusSubExpressions in class Expression

Returns:

an iterator containing those sub-expressions of this expression that are evaluated with the same focus as the parent expression

hasLoopingSubexpression

public boolean hasLoopingSubexpression(Expression child)

Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly

Overrides:

hasLoopingSubexpression in class Expression

Parameters:

child - the immediate subexpression

Returns:

true if the child expression is evaluated repeatedly

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)

Replace one subexpression by a replacement subexpression

Overrides:

replaceSubExpression in class Expression

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

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,
                                   StaticContext env,
                                   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

env - the static context

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

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

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

Specified by:

iterate in interface SequenceIterable

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

Parameters:

context - The processing context. This is supplied only for mapping constructs that set the context node, position, and size. Otherwise it is null.

Returns:

either (a) a SequenceIterator over the sequence of items that the supplied input item maps to, or (b) an Item if it maps to a single item, or (c) null if it maps to an empty sequence.

Throws:

XPathException

explain

public void explain(ExpressionPresenter out)

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

Specified by:

explain in class Expression

Parameters:

out - the expression presenter used to display the structure

explainThreads

protected void explainThreads(ExpressionPresenter out)