net.sf.saxon.instruct

Class ComputedAttribute

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

public final class ComputedAttribute
extends SimpleNodeConstructor

An instruction derived from an xsl:attribute element in stylesheet, or from an attribute constructor in XQuery, in cases where the attribute name is not known statically

Field Summary

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

select

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD, locationId, staticProperties

Constructor Summary

ComputedAttribute(Expression attributeName, Expression namespace, NamespaceResolver nsContext, int validationAction, SimpleType schemaType, int annotation, boolean allowNameAsQName)
Construct an Attribute instruction

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.
int
computeSpecialProperties()
Get the static properties of this expression (other than its type).
Expression
copy()
Copy an expression.
int
evaluateNameCode(XPathContext context)
Determine the name to be used for the attribute, as an integer name code
void
explain(ExpressionPresenter out)
Diagnostic print of expression structure.
int
getCardinality()
Get the static cardinality of this expression
int
getInstructionNameCode()
Get the name of this instruction
ItemType
getItemType(TypeHierarchy th)
Get the static type of this expression
Expression
getNameExpression()
Get the expression used to compute the name of the attribute
Expression
getNamespaceExpression()
Get the expression used to compute the namespace part of the name of the attribute
NamespaceResolver
getNamespaceResolver()
Get the namespace resolver used to resolve any prefix in the name of the attribute
Iterator
iterateSubExpressions()
Get the subexpressions of this expression
void
localTypeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Method to perform type-checking specific to the kind of instruction
Expression
optimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
TailCall
processLeavingTail(XPathContext context)
Process this instruction
protected void
promoteInst(PromotionOffer offer)
Offer promotion for subexpressions.
boolean
replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression
void
setRejectDuplicates()
Indicate that two attributes with the same name are not acceptable.
Expression
simplify(ExpressionVisitor visitor)
Simplify an expression.

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

checkContent, computeCardinality, computeSpecialProperties, createsNewNodes, evaluateItem, evaluateNameCode, expandChildren, getSelect, iterate, iterateSubExpressions, localTypeCheck, optimize, promoteInst, replaceSubExpression, setSelect, 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

ComputedAttribute

public ComputedAttribute(Expression attributeName,
                         Expression namespace,
                         NamespaceResolver nsContext,
                         int validationAction,
                         SimpleType schemaType,
                         int annotation,
                         boolean allowNameAsQName)
Construct an Attribute instruction
Parameters:
attributeName - An expression to calculate the attribute name
namespace - An expression to calculate the attribute namespace
nsContext - a NamespaceContext object containing the static namespace context of the stylesheet instruction
validationAction - e.g. validation=strict, lax, strip, preserve
schemaType - Type against which the attribute must be validated. This must not be a namespace-sensitive type; it is the caller's responsibility to check this.
annotation - Integer code identifying the type named in the type attribute
allowNameAsQName - true if the attributeName expression is allowed to evaluate to a value of type xs:QName (true in XQuery, false in XSLT)

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

computeSpecialProperties

public int computeSpecialProperties()
Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.
Overrides:
computeSpecialProperties in interface SimpleNodeConstructor
Returns:
a set of flags indicating static properties of this 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

evaluateNameCode

public int evaluateNameCode(XPathContext context)
            throws XPathException
Determine the name to be used for the attribute, as an integer name code
Overrides:
evaluateNameCode in interface SimpleNodeConstructor
Parameters:
context - Dynamic evaluation context
Returns:
the integer name code for the attribute name
Throws:
XPathException -

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

getCardinality

public int getCardinality()
Get the static cardinality of this expression
Overrides:
getCardinality in interface Expression
Returns:
the static cardinality (exactly one)

getInstructionNameCode

public int getInstructionNameCode()
Get the name of this instruction
Overrides:
getInstructionNameCode in interface Instruction

getItemType

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

getNameExpression

public Expression getNameExpression()
Get the expression used to compute the name of the attribute
Returns:
the expression used to compute the name of the attribute

getNamespaceExpression

public Expression getNamespaceExpression()
Get the expression used to compute the namespace part of the name of the attribute
Returns:
the expression used to compute the namespace part of the name of the attribute

getNamespaceResolver

public NamespaceResolver getNamespaceResolver()
Get the namespace resolver used to resolve any prefix in the name of the attribute
Returns:
the namespace resolver if one has been saved; or null otherwise

iterateSubExpressions

public Iterator iterateSubExpressions()
Get the subexpressions of this expression
Overrides:
iterateSubExpressions in interface SimpleNodeConstructor
Returns:
an iterator over the subexpressions

localTypeCheck

public void localTypeCheck(ExpressionVisitor visitor,
                           ItemType contextItemType)
            throws XPathException
Method to perform type-checking specific to the kind of instruction
Overrides:
localTypeCheck in interface SimpleNodeConstructor
Parameters:
visitor - an expression visitor
contextItemType - the static type of the context item
Throws:
XPathException -

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 SimpleNodeConstructor
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)

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
            throws XPathException
Process this instruction
Specified by:
processLeavingTail in interface TailCallReturner
Overrides:
processLeavingTail in interface Instruction
Parameters:
context - the dynamic context of the transformation
Returns:
a TailCall to be executed by the caller, always null for this instruction

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 SimpleNodeConstructor
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 SimpleNodeConstructor
Parameters:
original - the original subexpression
replacement - the replacement subexpression
Returns:
true if the original subexpression is found

setRejectDuplicates

public void setRejectDuplicates()
Indicate that two attributes with the same name are not acceptable. (This option is set in XQuery, but not in XSLT)

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 SimpleNodeConstructor
Parameters:
visitor - an expression visitor
Returns:
the simplified expression
Throws:
XPathException - if an error is discovered during expression rewriting