net.sf.saxon.instruct
Class ComputedElement

java.lang.Object
  net.sf.saxon.expr.Expression
      net.sf.saxon.instruct.Instruction
          net.sf.saxon.instruct.ParentNodeConstructor
              net.sf.saxon.instruct.ElementCreator
                  net.sf.saxon.instruct.ComputedElement

All Implemented Interfaces:

Serializable, SourceLocator, EvaluableItem, SequenceIterable, TailCallReturner, InstructionInfoProvider

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, Serialized Form

Field Summary

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

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

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) Get the base URI for the element being constructed
Iterator	iterateSubExpressions() Get the immediate sub-expressions of this expression.
Expression	optimize(ExpressionVisitor visitor, ItemType contextItemType) Perform optimisation of an expression and its 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

computeSpecialProperties, evaluateItem, getActiveNamespaces, getImplementationMethod, isInheritNamespaces, isPreservingTypes, iterateEvents, processLeavingTail, setValidationMode, suppressValidation

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

addToPathMap, computeCardinality, createsNewNodes, getBaseURI, getCardinality, getContentExpression, getSchemaType, getValidationMode, isLazyConstruction, isNamespaceSensitive, setBaseURI, setContentExpression, setLazyConstruction, setSchemaType

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

evaluateAsString, getInstructionInfo, getSourceLocator, isXSLT, iterate, process, promote

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

adoptChildExpression, computeDependencies, computeStaticProperties, display, doPromotion, effectiveBooleanValue, explain, findParentOf, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, markTailFunctionCalls, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, toString

Methods inherited from class java.lang.Object

equals, 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.

schemaType - The required schema type for the content

allowQName -

Method Detail

getNameExpression

public Expression getNameExpression()

getNamespaceExpression

public Expression getNamespaceExpression()

getNamespaceResolver

public NamespaceResolver getNamespaceResolver()

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException

Description copied from class: ParentNodeConstructor

Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.

Overrides:

simplify in class 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

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 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 class 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)

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 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)

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(TypeHierarchy th)

Get the item type of the value returned by this instruction

Overrides:

getItemType in class ElementCreator

Parameters:

th - the type hierarchy cache

Returns:

the item type

iterateSubExpressions

public Iterator iterateSubExpressions()

Description copied from class: ParentNodeConstructor

Get the immediate sub-expressions of this expression.

Overrides:

iterateSubExpressions in class ParentNodeConstructor

Returns:

an iterator containing the sub-expressions of this expression

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)

Replace one subexpression by a replacement subexpression

Overrides:

replaceSubExpression in class ParentNodeConstructor

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

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

getNameCode

public int getNameCode(XPathContext context)
                throws XPathException

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

Specified by:

getNameCode in class ElementCreator

Parameters:

context - The evaluation context (not used)

Returns:

the name code for the element name

Throws:

XPathException - if a failure occurs

getNewBaseURI

public String getNewBaseURI(XPathContext context)

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

Returns:

the base URI of the constructed element

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

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