net.sf.saxon.expr.instruct
Class ComputedElement

java.lang.Object
  extended by net.sf.saxon.expr.Expression
      extended by net.sf.saxon.expr.instruct.Instruction
          extended by net.sf.saxon.expr.instruct.ParentNodeConstructor
              extended by net.sf.saxon.expr.instruct.ElementCreator
                  extended by net.sf.saxon.expr.instruct.ComputedElement
All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, DivisibleInstruction, TailCallReturner, ValidatingInstruction, InstructionInfo, Locator

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.instruct.ElementCreator
inheritNamespaces
 
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, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, WATCH_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.
 NodeName getElementName(XPathContext context, NodeInfo copiedNode)
          Callback from the superclass ElementCreator to get the nameCode for the element name
 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
 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.
 Iterator<Expression> iterateSubExpressions()
          Get the immediate sub-expressions of this expression.
 Expression optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)
          Perform optimisation of an expression and its subexpressions.
protected  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 replaceSubExpression(Expression original, Expression replacement)
          Replace one subexpression by a replacement subexpression
 Expression simplify(ExpressionVisitor visitor)
          Simplify an expression.
 Expression typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)
          Perform type checking of an expression and its subexpressions.
 
Methods inherited from class net.sf.saxon.expr.instruct.ElementCreator
checkContentSequence, computeSpecialProperties, evaluateItem, getActiveNamespaces, getImplementationMethod, isInheritNamespaces, iterateEvents, iterateEvents, processLeavingTail, processLeavingTail, processLeft, processLeft, processRight, suppressValidation
 
Methods inherited from class net.sf.saxon.expr.instruct.ParentNodeConstructor
addToPathMap, computeCardinality, createsNewNodes, getBaseURI, getCardinality, getContentExpression, getSchemaType, getValidationAction, isLazyConstruction, isNamespaceSensitive, isPreservingTypes, setBaseURI, setContentExpression, setLazyConstruction, setNoNeedToStrip, setSchemaType, setValidationAction
 
Methods inherited from class net.sf.saxon.expr.instruct.Instruction
assembleParams, assembleTunnelParams, dynamicError, evaluateAsString, getConstructType, getExpressionName, getInstructionName, getIteratorFromProcessMethod, getSourceLocator, isXSLT, iterate, process, promote
 
Methods inherited from class net.sf.saxon.expr.Expression
adoptChildExpression, checkForUpdatingSubexpressions, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluatePendingUpdates, explain, getColumnNumber, getColumnNumber, getContainer, getDependencies, getEvaluationMethod, getExecutable, getHostLanguage, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateSameFocusSubExpressions, markTailFunctionCalls, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, toString, typeError
 
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: 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,
                            ExpressionVisitor.ContextItemType 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 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,
                           ExpressionVisitor.ContextItemType 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<Expression> 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

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

protected 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

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


Copyright (c) 2004-2011 Saxonica Limited. All rights reserved.