Class ComputedElement

All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, TailCallReturner, 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:
  • Constructor Details

    • 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 (that is, true in XQuery, false in XSLT).
  • Method Details

    • 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, 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
    • 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
    • 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
    • outputNamespaceNodes

      protected void outputNamespaceNodes(XPathContext context, Receiver out) 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
      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