Class Choose

All Implemented Interfaces:
Serializable, SourceLocator, Container, Expression, TailCallReturner, InstructionInfoProvider

public class Choose extends Instruction
Compiled representation of an xsl:choose or xsl:if element in the stylesheet. Also used for typeswitch in XQuery.
See Also:
  • Constructor Details

    • Choose

      public Choose(Expression[] conditions, Expression[] actions)
      Construct an xsl:choose instruction
      Parameters:
      conditions - the conditions to be tested, in order
      actions - the actions to be taken when the corresponding condition is true
  • Method Details

    • getInstructionNameCode

      public int getInstructionNameCode()
      Get the name of this instruction for diagnostic and tracing purposes We assume that if there was only one condition then it was an xsl:if; this is not necessarily so, but it's adequate for tracing purposes.
      Overrides:
      getInstructionNameCode in class Instruction
    • simplify

      public Expression simplify(StaticContext env) throws XPathException
      Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression).
      Specified by:
      simplify in interface Expression
      Specified by:
      simplify in class Instruction
      Parameters:
      env - the static context
      Returns:
      the simplified expression
      Throws:
      XPathException - if an error is discovered during expression rewriting
    • typeCheck

      public Expression typeCheck(StaticContext env, ItemType contextItemType) throws XPathException
      Description copied from interface: 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.

      Parameters:
      env - the static context of the expression
      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
    • optimize

      public Expression optimize(Optimizer opt, StaticContext env, ItemType contextItemType) throws XPathException
      Description copied from interface: 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.

      Parameters:
      opt - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.
      env - the static context of the expression
      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
    • getImplementationMethod

      public int getImplementationMethod()
      An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is prefered. For instructions this is the process() method.
      Specified by:
      getImplementationMethod in interface Expression
      Overrides:
      getImplementationMethod in class Instruction
    • markTailFunctionCalls

      public boolean markTailFunctionCalls(int nameCode, int arity)
      Mark tail calls on used-defined functions. For most expressions, this does nothing.
      Overrides:
      markTailFunctionCalls in class ComputedExpression
      Returns:
      true if a tail recursive call was found and if this call accounts for the whole of the value.
    • getItemType

      public ItemType getItemType(TypeHierarchy th)
      Get the item type of the items returned by evaluating this instruction
      Specified by:
      getItemType in interface Expression
      Overrides:
      getItemType in class Instruction
      Parameters:
      th -
      Returns:
      the static item type of the instruction
    • createsNewNodes

      public final boolean createsNewNodes()
      Determine whether this instruction creates new nodes. This implementation returns true if any of the "actions" creates new nodes. (Nodes created by the conditions can't contribute to the result).
      Overrides:
      createsNewNodes in class Instruction
    • iterateSubExpressions

      public Iterator iterateSubExpressions()
      Get all the XPath expressions associated with this instruction (in XSLT terms, the expression present on attributes of the instruction, as distinct from the child instructions in a sequence construction)
      Specified by:
      iterateSubExpressions in interface Expression
      Overrides:
      iterateSubExpressions in class ComputedExpression
      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
      Specified by:
      replaceSubExpression in interface Container
      Overrides:
      replaceSubExpression in class ComputedExpression
      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
      Handle promotion offers, that is, non-local tree rewrites.
      Overrides:
      promoteInst in class Instruction
      Parameters:
      offer - The type of rewrite being offered
      Throws:
      XPathException
    • 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.
      Specified by:
      checkPermittedContents in interface Expression
      Overrides:
      checkPermittedContents in class ComputedExpression
      Parameters:
      parentType - The schema type
      env - the static context
      whole - true if this expression is expected to make the whole content of the type, false if it is expected to make up only a part
      Throws:
      XPathException - if the expression doesn't match the required content type
    • display

      public void display(int level, PrintStream out, Configuration config)
      Diagnostic print of expression structure. The expression is written to the System.err output stream
      Parameters:
      level - indentation level for this expression
      out -
      config -
    • processLeavingTail

      public TailCall processLeavingTail(XPathContext context) throws XPathException
      Process this instruction, that is, choose an xsl:when or xsl:otherwise child and process it.
      Specified by:
      processLeavingTail in interface TailCallReturner
      Specified by:
      processLeavingTail in class Instruction
      Parameters:
      context - the dynamic context of this transformation
      Returns:
      a TailCall, if the chosen branch ends with a call of call-template or apply-templates. It is the caller's responsibility to execute such a TailCall. If there is no TailCall, returns null.
      Throws:
      XPathException - if any non-recoverable dynamic error occurs
    • evaluateItem

      public Item evaluateItem(XPathContext context) throws XPathException
      Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.
      Specified by:
      evaluateItem in interface Expression
      Overrides:
      evaluateItem in class Instruction
      Parameters:
      context - The context in which the expression is to be evaluated
      Returns:
      the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
      Throws:
      XPathException - if any dynamic error occurs evaluating the expression
    • iterate

      public SequenceIterator iterate(XPathContext context) throws XPathException
      Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation relies on the process() method: it "pushes" the results of the instruction to a sequence in memory, and then iterates over this in-memory sequence. In principle instructions should implement a pipelined iterate() method that avoids the overhead of intermediate storage.
      Specified by:
      iterate in interface Expression
      Overrides:
      iterate in class Instruction
      Parameters:
      context - supplies the context for evaluation
      Returns:
      a SequenceIterator that can be used to iterate over the result of the expression
      Throws:
      XPathException - if any dynamic error occurs evaluating the expression