Package 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:
Serializable
,SourceLocator
,LocationProvider
,SaxonLocator
,Binding
,EvaluableItem
,SequenceIterable
,InstructionInfo
,Locator
A ForExpression maps an expression over a sequence.
This version works with range variables, it doesn't change the context information
- See Also:
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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
EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties
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Constructor Summary
ConstructorsConstructorDescriptionCreate a "for" expression (for $x at $p in SEQUENCE return ACTION) -
Method Summary
Modifier and TypeMethodDescriptionvoid
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
Determine the static cardinality of the expressionconvertWhereToPredicate
(ExpressionVisitor visitor, ItemType contextItemType) Convert where clause, if possible, to a predicate.copy()
Copy an expression.void
evaluatePendingUpdates
(XPathContext context, PendingUpdateList pul) Evaluate an updating expression, adding the results to a Pending Update List.void
Diagnostic print of expression structure.protected Binding[]
extendBindingList
(Binding[] in) Extend an array of variable bindings to include the binding(s) defined in this expressionint
Get the type of this expression for use in tracing and diagnosticsint
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().Determine the data type of the items returned by the expression, if possibleGet the name of the position variableint
Get the number of slots required.boolean
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 repeatedlyiterate
(XPathContext context) Iterate over the sequence of valuesiterateEvents
(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.optimize
(ExpressionVisitor visitor, ItemType contextItemType) Optimize the expressionvoid
process
(XPathContext context) Process this expression as an instruction, writing results to the current outputtervoid
Set the reference to the position variable (XQuery only)void
setSlotNumber
(int nr) Set the slot number for the range variabletypeCheck
(ExpressionVisitor visitor, ItemType contextItemType) Type-check the expressionMethods inherited from class net.sf.saxon.expr.Assignation
addToPathMap, checkForUpdatingSubexpressions, evaluateVariable, getAction, getLocalSlotNumber, getObjectName, getRequiredType, getSequence, getVariableName, getVariableQName, isAssignable, isGlobal, isUpdatingExpression, iterateSubExpressions, promote, promoteWhereClause, refineTypeInformation, replaceSubExpression, setAction, setRequiredType, setSequence, setVariableQName, simplify, suppressValidation
Methods inherited from class net.sf.saxon.expr.Expression
adoptChildExpression, computeDependencies, computeSpecialProperties, computeStaticProperties, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, findParentOf, getCardinality, getColumnNumber, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, implementsStaticTypeCheck, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, toString, typeError
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Constructor Details
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ForExpression
public ForExpression()Create a "for" expression (for $x at $p in SEQUENCE return ACTION)
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Method Details
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setPositionVariable
Set the reference to the position variable (XQuery only)- Parameters:
decl
- the range variable declaration for the position variable
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getPositionVariableName
Get the name of the position variable- Returns:
- the name of the position variable ("at $p") if there is one, or null if not
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setSlotNumber
public void setSlotNumber(int nr) Set the slot number for the range variable- Overrides:
setSlotNumber
in classAssignation
- Parameters:
nr
- the slot number allocated to the range variable on the local stack frame. This implicitly allocates the next slot number to the position variable if there is one.
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getRequiredSlots
public int getRequiredSlots()Get the number of slots required.- Overrides:
getRequiredSlots
in classAssignation
- Returns:
- normally 1, except for a FOR expression with an AT clause, where it is 2.
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typeCheck
public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException Type-check the expression- Overrides:
typeCheck
in classExpression
- Parameters:
visitor
- an expression visitorcontextItemType
- 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 toType.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)
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optimize
public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException Optimize the expression- Overrides:
optimize
in classExpression
- Parameters:
visitor
- an expression visitorcontextItemType
- 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 toType.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)
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hasLoopingSubexpression
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 classExpression
- Parameters:
child
- the immediate subexpression- Returns:
- true if the child expression is evaluated repeatedly
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convertWhereToPredicate
public Expression convertWhereToPredicate(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException Convert where clause, if possible, to a predicate.- Parameters:
visitor
- the expression visitorcontextItemType
- the item type of the context item- Returns:
- the converted expression if modified, or null otherwise
- Throws:
XPathException
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copy
Copy an expression. This makes a deep copy.- Specified by:
copy
in classExpression
- Returns:
- the copy of the original expression
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markTailFunctionCalls
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 classExpression
- Parameters:
qName
- the name of the functionarity
- the arity (number of parameters) of the function- Returns:
- 0 if no tail call was found; 1 if a tail call on a different function was found; 2 if a tail recursive call was found and if this call accounts for the whole of the value.
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extendBindingList
Extend an array of variable bindings to include the binding(s) defined in this expression- Overrides:
extendBindingList
in classAssignation
- Parameters:
in
- a set of variable bindings- Returns:
- a set of variable bindings including all those supplied plus this one
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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 classExpression
- Returns:
- the implementation method, for example
Expression.ITERATE_METHOD
orExpression.EVALUATE_METHOD
orExpression.PROCESS_METHOD
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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 classExpression
- 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 typeenv
- the static contextwhole
- 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
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iterate
Iterate over the sequence of values- Specified by:
iterate
in interfaceSequenceIterable
- Overrides:
iterate
in classExpression
- 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
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iterateEvents
Deliver the result of the expression as a sequence of events.- Overrides:
iterateEvents
in classExpression
- 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
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process
Process this expression as an instruction, writing results to the current outputter- Overrides:
process
in classExpression
- Parameters:
context
- The dynamic context, giving access to the current node, the current variables, etc.- Throws:
XPathException
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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 classExpression
- Parameters:
context
- the XPath dynamic evaluation contextpul
- the pending update list to which the results should be written- Throws:
XPathException
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getItemType
Determine the data type of the items returned by the expression, if possible- Specified by:
getItemType
in classExpression
- Parameters:
th
- the type hierarchy cache- Returns:
- one of the values Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known in advance)
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computeCardinality
public int computeCardinality()Determine the static cardinality of the expression- Specified by:
computeCardinality
in classExpression
- 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
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explain
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.- Specified by:
explain
in classExpression
- Parameters:
out
- the expression presenter used to display the structure
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getConstructType
public int getConstructType()Get the type of this expression for use in tracing and diagnostics- Specified by:
getConstructType
in interfaceInstructionInfo
- Overrides:
getConstructType
in classExpression
- Returns:
- the type of expression, as enumerated in class
Location
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