net.sf.saxon.instruct

Class ComputedElement

Implemented Interfaces:
SourceLocator, EvaluableItem, InstructionInfoProvider, SequenceIterable, Serializable, SourceLocator, TailCallReturner

public class ComputedElement
extends ElementCreator

An instruction representing an xsl:element element in an XSLT stylesheet, or a computed element constructor in XQuery. (In both cases, if the element name is expressed as a compile-time expression, then a FixedElement instruction is used instead.)
See Also:
FixedElement

Field Summary

Fields inherited from class net.sf.saxon.instruct.ElementCreator

inheritNamespaces, preservingTypes

Fields inherited from class net.sf.saxon.instruct.ParentNodeConstructor

content

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD, locationId, staticProperties

Constructor Summary

ComputedElement(Expression elementName, Expression namespace, NamespaceResolver nsContext, String defaultNamespace, SchemaType schemaType, int validation, boolean inheritNamespaces, boolean allowQName)
Create an instruction that creates a new element node

Method Summary

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.
Expression
copy()
Copy an expression.
void
explain(ExpressionPresenter out)
Diagnostic print of expression structure.
int
getInstructionNameCode()
Get the name of this instruction for diagnostic and tracing purposes
ItemType
getItemType(TypeHierarchy th)
Get the item type of the value returned by this instruction
int
getNameCode(XPathContext context)
Callback from the superclass ElementCreator to get the nameCode for the element name
Expression
getNameExpression()
Expression
getNamespaceExpression()
NamespaceResolver
getNamespaceResolver()
String
getNewBaseURI(XPathContext context)
Iterator
iterateSubExpressions()
Get the immediate sub-expressions of this expression.
Expression
optimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
protected void
outputNamespaceNodes(XPathContext context, Receiver out)
Callback to output namespace nodes for the new element.
protected void
promoteInst(PromotionOffer offer)
Offer promotion for subexpressions.
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.instruct.ElementCreator

checkContentSequence, computeSpecialProperties, evaluateItem, getActiveNamespaces, getImplementationMethod, getItemType, getNameCode, getNewBaseURI, isInheritNamespaces, isPreservingTypes, iterateEvents, outputNamespaceNodes, processLeavingTail, setValidationMode, suppressValidation

Methods inherited from class net.sf.saxon.instruct.ParentNodeConstructor

addToPathMap, checkContentSequence, computeCardinality, createsNewNodes, getBaseURI, getCardinality, getContentExpression, getSchemaType, getValidationMode, isLazyConstruction, isNamespaceSensitive, iterateSubExpressions, optimize, promoteInst, replaceSubExpression, setBaseURI, setContentExpression, setLazyConstruction, setSchemaType, setValidationMode, simplify, typeCheck

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

assembleParams, assembleTunnelParams, computeCardinality, computeSpecialProperties, createsNewNodes, dynamicError, evaluateAsString, evaluateItem, getImplementationMethod, getInstructionInfo, getInstructionNameCode, getItemType, getSourceLocator, isXSLT, iterate, process, processLeavingTail, promote, promoteInst, simplify

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

addToPathMap, adoptChildExpression, checkPermittedContents, computeCardinality, computeDependencies, computeSpecialProperties, computeStaticProperties, copy, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, explain, findParentOf, getCardinality, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getItemType, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterate, iterateEvents, iterateSubExpressions, markTailFunctionCalls, optimize, process, promote, replaceSubExpression, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toString, typeCheck, typeError

Constructor Details

ComputedElement

public ComputedElement(Expression elementName,
                       Expression namespace,
                       NamespaceResolver nsContext,
                       String defaultNamespace,
                       SchemaType schemaType,
                       int validation,
                       boolean inheritNamespaces,
                       boolean allowQName)
Create an instruction that creates a new element node
Parameters:
elementName - Expression that evaluates to produce the name of the element node as a lexical QName
namespace - Expression that evaluates to produce the namespace URI of the element node. Set to null if the namespace is to be deduced from the prefix of the elementName.
nsContext - Saved copy of the static namespace context for the instruction. Can be set to null if namespace is supplied.
schemaType - The required schema type for the content
allowQName -

Method Details

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 interface Expression

copy

public Expression copy()
Copy an expression. This makes a deep copy.
Overrides:
copy in interface Expression
Returns:
the copy of the original expression

explain

public void explain(ExpressionPresenter out)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
Overrides:
explain in interface Expression

getInstructionNameCode

public int getInstructionNameCode()
Get the name of this instruction for diagnostic and tracing purposes
Overrides:
getInstructionNameCode in interface Instruction

getItemType

public ItemType getItemType(TypeHierarchy th)
Get the item type of the value returned by this instruction
Overrides:
getItemType in interface ElementCreator
Parameters:
th - the type hierarchy cache
Returns:
the item type

getNameCode

public int getNameCode(XPathContext context)
            throws XPathException
Callback from the superclass ElementCreator to get the nameCode for the element name
Overrides:
getNameCode in interface ElementCreator
Parameters:
context - The evaluation context (not used)
Returns:
the name code for the element name

getNameExpression

public Expression getNameExpression()

getNamespaceExpression

public Expression getNamespaceExpression()

getNamespaceResolver

public NamespaceResolver getNamespaceResolver()

getNewBaseURI

public String getNewBaseURI(XPathContext context)
Overrides:
getNewBaseURI in interface ElementCreator

iterateSubExpressions

public Iterator iterateSubExpressions()
Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.
Overrides:
iterateSubExpressions in interface ParentNodeConstructor
Returns:
an iterator containing the sub-expressions of this expression

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ItemType contextItemType)
            throws XPathException
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 interface ParentNodeConstructor
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)

outputNamespaceNodes

protected void outputNamespaceNodes(XPathContext context,
                                    Receiver out)
            throws XPathException
Callback to output namespace nodes for the new element.
Overrides:
outputNamespaceNodes in interface ElementCreator
Parameters:
context - The execution context
out - the Receiver where the namespace nodes are to be written
Throws:
XPathException -

promoteInst

protected void promoteInst(PromotionOffer offer)
            throws XPathException
Offer promotion for subexpressions. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is not accepted - this is appropriate in the case of simple expressions such as constant values and variable references where promotion would give no performance advantage. This method is always called at compile time.
Overrides:
promoteInst in interface ParentNodeConstructor
Parameters:
offer - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression
Throws:
XPathException - if any error is detected

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)
Replace one subexpression by a replacement subexpression
Overrides:
replaceSubExpression in interface ParentNodeConstructor
Parameters:
original - the original subexpression
replacement - the replacement subexpression
Returns:
true if the original subexpression is found

simplify

public Expression simplify(ExpressionVisitor visitor)
            throws XPathException
Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.
Overrides:
simplify in interface ParentNodeConstructor
Parameters:
visitor - an 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
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 parent pointer and 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 interface ParentNodeConstructor
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)