## net.sf.saxon.instruct
Class ComputedAttribute

    java.lang.Object
      net.sf.saxon.expr.Expression
          net.sf.saxon.instruct.Instruction
              net.sf.saxon.instruct.SimpleNodeConstructor
                  net.sf.saxon.instruct.AttributeCreator
                      net.sf.saxon.instruct.ComputedAttribute

All Implemented Interfaces:
  java.io.Serializable, javax.xml.transform.SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, TailCallReturner, InstructionInfo, org.xml.sax.Locator

    public final class ComputedAttribute

extends AttributeCreator

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

See Also:
  Serialized Form

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, locationId, PROCESS_METHOD, 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
`java.util.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.AttributeCreator
`getAnnotation, getOptions, getSchemaType, getValidationAction, setAnnotation, setNoSpecialChars, setOptions, setSchemaType, setValidationAction`

Methods inherited from class net.sf.saxon.instruct.SimpleNodeConstructor
`checkContent, computeCardinality, createsNewNodes, evaluateItem, expandChildren, getSelect, iterate, setSelect, typeCheck`

Methods inherited from class net.sf.saxon.instruct.Instruction
`assembleParams, assembleTunnelParams, dynamicError, evaluateAsString, getConstructType, getImplementationMethod, getSourceLocator, isXSLT, process, promote`

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

`addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, computeDependencies, computeStaticProperties, display, doPromotion, dynamicError, effectiveBooleanValue, evaluatePendingUpdates, explain, findParentOf, getColumnNumber, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, isUpdatingExpression, iterateEvents, markTailFunctionCalls, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, 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

### 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 Detail

### 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)

  Overrides:
    `setRejectDuplicates` in class `AttributeCreator`

### getInstructionNameCode

    public int getInstructionNameCode()

  Get the name of this instruction

  Overrides:
    `getInstructionNameCode` in class `Instruction`
  Returns:
    a code identifying the instruction: typically but not always the fingerprint of a name in the XSLT namespace

### 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

### getItemType

    public ItemType getItemType(TypeHierarchy th)

  Get the static type of this expression

  Overrides:
    `getItemType` in class `Instruction`
  Parameters:
    `th` - the type hierarchy cache
  Returns:
    the static type of the item returned by this expression

### getCardinality

    public int getCardinality()

  Get the static cardinality of this expression

  Overrides:
    `getCardinality` in class `Expression`
  Returns:
    the static cardinality (exactly one)

### 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 class `SimpleNodeConstructor`
  Returns:
    a set of flags indicating static properties of this expression

### simplify

    public Expression simplify(ExpressionVisitor visitor)
                        throws XPathException

  Description copied from class: `Instruction`
  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 `SimpleNodeConstructor`
  Parameters:
    `visitor` - an expression visitor
  Returns:
    the simplified expression
  Throws:
    `XPathException` - if an error is discovered during expression rewriting

### localTypeCheck

    public void localTypeCheck(ExpressionVisitor visitor,
                               ItemType contextItemType)
                        throws XPathException

  Description copied from class: `SimpleNodeConstructor`
  Method to perform type-checking specific to the kind of instruction

  Specified by:
    `localTypeCheck` in class `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

  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 `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)

### 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

### iterateSubExpressions

    public java.util.Iterator iterateSubExpressions()

  Get the subexpressions of this expression

  Overrides:
    `iterateSubExpressions` in class `SimpleNodeConstructor`
  Returns:
    an iterator over the subexpressions

### replaceSubExpression

    public boolean replaceSubExpression(Expression original,
                                        Expression replacement)

  Replace one subexpression by a replacement subexpression

  Overrides:
    `replaceSubExpression` in class `SimpleNodeConstructor`
  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 `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

### 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

### processLeavingTail

    public TailCall processLeavingTail(XPathContext context)
                                throws XPathException

  Process this instruction

  Specified by:
    `processLeavingTail` in interface `TailCallReturner`
  Specified by:
    `processLeavingTail` in class `Instruction`
  Parameters:
    `context` - the dynamic context of the transformation
  Returns:
    a TailCall to be executed by the caller, always null for this instruction
  Throws:
    `XPathException`

### 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 class `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.

  Specified by:
    `explain` in class `Expression`
  Parameters:
    `out` - the expression presenter used to display the structure

Copyright (c) Saxonica Limited. All rights reserved.