net.sf.saxon.expr

Class ForExpression

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.Assignation

net.sf.saxon.expr.ForExpression

All Implemented Interfaces:

SourceLocator, Binding, LocalBinding, IdentityComparable, InstructionInfo

Direct Known Subclasses:

OuterForExpression

public class ForExpression
extends Assignation

A ForExpression maps an expression over a sequence. We use a ForExpression in preference to a FLWORExpression to handle simple cases (roughly, the XPath subset). In 9.6, we no longer convert a FLWORExpression to a ForExpression if there is a position variable, which simplifies the cases this class has to handle.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected static class	ForExpression.EventMappingAction The EventMappingAction represents the action to be taken for each item in the source sequence.
static class	ForExpression.MappingAction The MappingAction represents the action to be taken for each item in the source sequence.

Field Summary

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

action, requiredType, sequence, slotNumber, variableName

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

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

Constructor Summary

Constructors

Constructor and Description
ForExpression() Create a "for" expression (for $x at $p in SEQUENCE return ACTION)

Method Summary

Methods

Modifier and Type	Method and Description
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	computeCardinality() Determine the static cardinality of the expression
Expression	copy() Copy an expression.
void	evaluatePendingUpdates(XPathContext context, PendingUpdateList pul) Evaluate an updating expression, adding the results to a Pending Update List.
void	explain(ExpressionPresenter out) Diagnostic print of expression structure.
protected void	explainSpecializedAttributes(ExpressionPresenter out)
int	getConstructType() Get the type of this expression for use in tracing and diagnostics
ExpressionCompiler	getExpressionCompiler() Return the compiler of the For expression
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().
IntegerValue[]	getIntegerBounds() For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis.
ItemType	getItemType() Determine the data type of the items returned by the expression, if possible
protected int	getRangeVariableCardinality() Get the cardinality of the range variable
protected StreamingAdjunct	getStreamingAdjunct() Get a class that supports streamed evaluation of this expression
boolean	hasVariableBinding(Binding binding)
boolean	isVacuousExpression() Determine whether this is a vacuous expression as defined in the XQuery update specification
SequenceIterator	iterate(XPathContext context) Iterate over the sequence of values
EventIterator	iterateEvents(XPathContext context) Deliver the result of the expression as a sequence of events.
int	markTailFunctionCalls(StructuredQName qName, int arity) Mark tail function calls: only possible if the for expression iterates zero or one times.
Expression	optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) Optimize the expression
void	process(XPathContext context) Process this expression as an instruction, writing results to the current outputter
protected Expression	promoteWhereClause() Promote a WHERE clause whose condition doesn't depend on the variable being bound.
String	toString() The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.
Expression	typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Type-check the expression
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.Assignation

addReference, addToPathMap, checkForUpdatingSubexpressions, evaluateVariable, extendBindingList, getAction, getIntegerBoundsForVariable, getLocalSlotNumber, getNominalReferenceCount, getObjectName, getRequiredSlots, getRequiredType, getSequence, getVariableEQName, getVariableName, getVariableQName, isAssignable, isGlobal, isIndexedVariable, isUpdatingExpression, operands, promote, refineTypeInformation, replaceOperand, replaceVariable, setAction, setIndexedVariable, setRequiredType, setSequence, setSlotNumber, setVariableQName, suppressValidation

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

adoptChildExpression, clearStreamabilityData, computeDependencies, computeSpecialProperties, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, getCardinality, getColumnNumber, getConfiguration, getContainer, getDependencies, getEvaluationMethod, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLocationId, getPosture, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getStreamability, getSweep, getSystemId, identityHashCode, implementsStaticTypeCheck, isIdentical, isSubtreeExpression, makeStreamingAdjunct, operandList, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, setPostureAndSweep, simplify, staticTypeCheck, toPattern, toShortString, toStreamingPattern, typeError

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

ForExpression

public ForExpression()

Create a "for" expression (for $x at $p in SEQUENCE return ACTION)

Method Detail

getExpressionName

public 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.

hasVariableBinding

public boolean hasVariableBinding(Binding binding)

Overrides:

hasVariableBinding in class Assignation

typeCheck

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

Type-check the expression

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)

getRangeVariableCardinality

protected int getRangeVariableCardinality()

Get the cardinality of the range variable

Returns:

the cardinality of the range variable (StaticProperty.EXACTLY_ONE). Can be overridden in a subclass

optimize

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

Optimize the expression

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)

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 Assignation

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

getIntegerBounds

public IntegerValue[] getIntegerBounds()

For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis. The default implementation returns null, meaning "unknown" or "not applicable". Other implementations return an array of two IntegerValue objects, representing the lower and upper bounds respectively. The values UNBOUNDED_LOWER and UNBOUNDED_UPPER are used by convention to indicate that the value may be arbitrarily large. The values MAX_STRING_LENGTH and MAX_SEQUENCE_LENGTH are used to indicate values limited by the size of a string or the size of a sequence.

Overrides:

getIntegerBounds in class Expression

Returns:

the lower and upper bounds of integer values in the result, or null to indicate unknown or not applicable.

promoteWhereClause

protected Expression promoteWhereClause()

Promote a WHERE clause whose condition doesn't depend on the variable being bound. This rewrites an expression of the form

let $i := SEQ return if (C) then R else ()

to the form:

if (C) then (let $i := SEQ return R) else ()

Returns:

an expression in which terms from the WHERE clause that can be extracted have been extracted

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

markTailFunctionCalls

public int markTailFunctionCalls(StructuredQName qName,
                        int arity)

Mark tail function calls: only possible if the for expression iterates zero or one times. (This arises in XSLT/XPath, which does not have a LET expression, so FOR gets used instead)

Overrides:

markTailFunctionCalls in class Expression

Parameters:

qName - the name of the function

arity - the arity (number of parameters) of the function

Returns:

UserFunctionCall.NOT_TAIL_CALL if no tail call was found; UserFunctionCall.FOREIGN_TAIL_CALL if a tail call on a different function was found;

isVacuousExpression

public boolean isVacuousExpression()

Determine whether this is a vacuous expression as defined in the XQuery update specification

Overrides:

isVacuousExpression in class Expression

Returns:

true if this expression is vacuous

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 Expression

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

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Iterate over the sequence of values

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

iterateEvents

public EventIterator iterateEvents(XPathContext context)
                            throws XPathException

Deliver the result of the expression as a sequence of events.

Overrides:

iterateEvents in class Expression

Parameters:

context - The dynamic evaluation context

Returns:

the result of the expression as an iterator over a sequence of PullEvent objects

Throws:

XPathException - if a dynamic error occurs during expression evaluation

process

public void process(XPathContext context)
             throws XPathException

Process this expression as an instruction, writing results to the current outputter

Overrides:

process in class Expression

Parameters:

context - The dynamic context, giving access to the current node, the current variables, etc.

Throws:

XPathException - if a dynamic error occurs

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

getItemType

public ItemType getItemType()

Determine the data type of the items returned by the expression, if possible

Specified by:

getItemType in class Expression

Returns:

one of the values Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known in advance)

computeCardinality

public int computeCardinality()

Determine the static cardinality of the expression

Specified by:

computeCardinality in class Expression

Returns:

the computed cardinality, as one of the values StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.EXACTLY_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_MORE

toString

public String toString()

The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax

Overrides:

toString in class Expression

Returns:

a representation of the expression as a string

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

explainSpecializedAttributes

protected void explainSpecializedAttributes(ExpressionPresenter out)

getExpressionCompiler

public ExpressionCompiler getExpressionCompiler()

Return the compiler of the For expression

Overrides:

getExpressionCompiler in class Expression

Returns:

the relevant ExpressionCompiler

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

getStreamingAdjunct

protected StreamingAdjunct getStreamingAdjunct()

Get a class that supports streamed evaluation of this expression

Overrides:

getStreamingAdjunct in class Expression

Returns:

the relevant StreamingAdjunct, or null if none is available