net.sf.saxon.expr.instruct

Class ComputedElement

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.instruct.Instruction

net.sf.saxon.expr.instruct.ParentNodeConstructor

net.sf.saxon.expr.instruct.ElementCreator

net.sf.saxon.expr.instruct.ComputedElement

All Implemented Interfaces:

SourceLocator, TailCallReturner, ValidatingInstruction, IdentityComparable, InstructionInfo

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.expr.instruct.ElementCreator

inheritNamespacesFromParent, inheritNamespacesToChildren, onEmpty

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

content, preservingTypes

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

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.
Expression	copy() Copy an expression.
void	explain(ExpressionPresenter out) Diagnostic print of expression structure.
NodeName	getElementName(XPathContext context, NodeInfo copiedNode) Callback from the superclass ElementCreator to get the nameCode for the element name
ExpressionCompiler	getExpressionCompiler() Return the compiler of the ComputedElement expression
int	getInstructionNameCode() Get the name of this instruction for diagnostic and tracing purposes
ItemType	getItemType() Get the item type of the value returned by this instruction
Expression	getNameExpression() Get the expression used to compute the element name
Expression	getNamespaceExpression() Get the expression used to compute the namespace URI
NamespaceResolver	getNamespaceResolver() Get the namespace resolver that provides the namespace bindings defined in the static context
String	getNewBaseURI(XPathContext context, NodeInfo copiedNode) Get the base URI for the element being constructed
boolean	isAllowNameAsQName() Ask whether the name can be supplied as a QName.
Iterable<Operand>	operands() Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.
Expression	optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) Perform optimisation of an expression and its subexpressions.
void	outputNamespaceNodes(XPathContext context, Receiver out, NodeName nameCode, NodeInfo copiedNode) Callback to output namespace nodes for the new element.
protected void	promoteInst(PromotionOffer offer) Offer promotion for subexpressions.
boolean	replaceOperand(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
Expression	simplify(ExpressionVisitor visitor) Simplify an expression.
Expression	typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Perform type checking of an expression and its subexpressions.

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

checkContentSequence, computeSpecialProperties, evaluateItem, getActiveNamespaces, getCardinality, getImplementationMethod, getOnEmpty, getStreamingAdjunct, isInheritNamespacesFromParent, isInheritNamespacesToChildren, iterateEvents, iterateEvents, processLeavingTail, processLeavingTail, setOnEmpty, suppressValidation

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

addToPathMap, computeCardinality, createsNewNodes, getBaseURI, getContentExpression, getSchemaType, getValidationAction, getValidationOptions, isLazyConstruction, isPreservingTypes, setBaseURI, setContentExpression, setLazyConstruction, setNoNeedToStrip, setValidationAction

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

assembleParams, assembleTunnelParams, dynamicError, evaluateAsString, getConstructType, getExpressionName, getInstructionName, getIteratorFromProcessMethod, getSourceLocator, isXSLT, iterate, process, promote, toStreamingPattern

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

adoptChildExpression, checkForUpdatingSubexpressions, clearStreamabilityData, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluatePendingUpdates, explain, getColumnNumber, getConfiguration, getContainer, getDependencies, getEvaluationMethod, getHostLanguage, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLocationId, getObjectName, getPosture, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getStreamability, getSweep, getSystemId, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isIdentical, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, makeStreamingAdjunct, markTailFunctionCalls, operandList, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, setPostureAndSweep, staticTypeCheck, toPattern, toShortString, toString, typeError, unordered

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

Constructor Detail

ComputedElement

public ComputedElement(Expression elementName,
               Expression namespace,
               NamespaceResolver nsContext,
               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. This namespace context must resolve the null prefix correctly, based on the different rules for XSLT and XQuery. //* @param defaultNamespace Default namespace to be used if no namespace is supplied and the //* computed element is a string with no prefix.

validation - Required validation mode (e.g. STRICT, LAX, SKIP)

inheritNamespaces - true if child elements automatically inherit the namespaces of their parent

schemaType - The required schema type for the content

allowQName - True if the elementName expression is allowed to return a QNameValue; false if it must return a string, and is cast to a string if necessary (that is, true in XQuery, false in XSLT).

Method Detail

getNameExpression

public Expression getNameExpression()

Get the expression used to compute the element name

Returns:

the expression used to compute the element name

getNamespaceExpression

public Expression getNamespaceExpression()

Get the expression used to compute the namespace URI

Returns:

the expression used to compute the namespace URI

getNamespaceResolver

public NamespaceResolver getNamespaceResolver()

Get the namespace resolver that provides the namespace bindings defined in the static context

Returns:

the namespace resolver

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException

Description copied from class: Expression

Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation simplifies its operands.

Overrides:

simplify in class ElementCreator

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,
                   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.

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 ElementCreator

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 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 ElementCreator

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)

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

getItemType

public ItemType getItemType()

Get the item type of the value returned by this instruction

Overrides:

getItemType in class ElementCreator

Returns:

the item type

operands

public Iterable<Operand> operands()

Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

Overrides:

operands in class ElementCreator

Returns:

an iterator containing the sub-expressions of this expression

replaceOperand

public boolean replaceOperand(Expression original,
                     Expression replacement)

Replace one subexpression by a replacement subexpression

Overrides:

replaceOperand in class ElementCreator

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

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 class 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

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

getElementName

public NodeName getElementName(XPathContext context,
                      NodeInfo copiedNode)
                        throws XPathException

Callback from the superclass ElementCreator to get the nameCode for the element name

Specified by:

getElementName in class ElementCreator

Parameters:

context - The evaluation context (not used)

copiedNode - Not applicable to this overload

Returns:

the name code for the element name

Throws:

XPathException - if a failure occurs

isAllowNameAsQName

public boolean isAllowNameAsQName()

Ask whether the name can be supplied as a QName. In practice this is true for XQuery, false for XSLT

Returns:

true if the name can be supplied as a QName

getNewBaseURI

public String getNewBaseURI(XPathContext context,
                   NodeInfo copiedNode)

Description copied from class: ElementCreator

Get the base URI for the element being constructed

Specified by:

getNewBaseURI in class ElementCreator

Parameters:

context - the XPath dynamic evaluation context

copiedNode - the node being copied (for xsl:copy), otherwise null

Returns:

the base URI of the constructed element

outputNamespaceNodes

public void outputNamespaceNodes(XPathContext context,
                        Receiver out,
                        NodeName nameCode,
                        NodeInfo copiedNode)
                          throws XPathException

Callback to output namespace nodes for the new element.

Specified by:

outputNamespaceNodes in class ElementCreator

Parameters:

context - The execution context

out - the Receiver where the namespace nodes are to be written

nameCode - The name of the element node being output

copiedNode - Where this is a copied node, the node being copied

Throws:

XPathException

getInstructionNameCode

public int getInstructionNameCode()

Get the name of this instruction for diagnostic and tracing purposes

Overrides:

getInstructionNameCode in class Instruction

Returns:

a code identifying the instruction: typically but not always the fingerprint of a name in the XSLT namespace

getExpressionCompiler

public ExpressionCompiler getExpressionCompiler()

Return the compiler of the ComputedElement expression

Overrides:

getExpressionCompiler in class Expression

Returns:

the relevant ExpressionCompiler

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