Package com.saxonica.ee.optim

Class SwitchExpression

java.lang.Object
net.sf.saxon.expr.Expression
com.saxonica.ee.optim.SwitchExpression
All Implemented Interfaces:
ExportAgent, ConditionalInstruction, Locatable, IdentityComparable, Traceable
public class SwitchExpression extends Expression implements ConditionalInstruction
An optimized Choose expression in which all the branches are tests of the same expression for equality with some value. Note this is not quite the same as the XQuery 3.1 switch expression; this switch expression is usually generated as the result of optimizing an xsl:choose or extended if/then/else expression.

  • Field Details

  • Constructor Details

    • SwitchExpression

      public SwitchExpression(SwitchExpression.SwitchCaseInfo switchCaseInfo)
      Create a switch expression
      Parameters:
      switchCaseInfo - details of the expression to be constructed

  • Method Details

    • setInstruction

      public void setInstruction(boolean inst)
      Say whether this switch expression originates as an XSLT instruction
      Parameters:
      inst - true if this started life as an xsl:choose instruction

    • isInstruction

      public boolean isInstruction()
      Ask whether this expression is an instruction. In XSLT streamability analysis this is used to distinguish constructs corresponding to XSLT instructions from other constructs.
      Overrides:
      isInstruction in class Expression
      Returns:
      true if this construct originates as an XSLT instruction

    • getSubjectExpression

      public Expression getSubjectExpression()
      Get the subject expression (the expression that computes the switch value)
      Returns:
      the expression that computes the switch value

    • getCaseMap

      public Map<AtomicMatchKey,Integer> getCaseMap()
      Get the map from XPathComparable objects representing the values to the expressions to be executed for each of these values
      Returns:
      the map of case clauses

    • getOtherwiseExpression

      public Expression getOtherwiseExpression()
      Get the default ("otherwise") expression
      Returns:
      the "otherwise" expression giving the value to be returned if none of the cases match

    • getAction

      public Operand getAction(int index)

    • getActions

      public List<Operand> getActions()

    • getOtherwiseOperand

      public Operand getOtherwiseOperand()

    • operands

      public Iterable<Operand> operands()
      Description copied from class: Expression
      Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.

      If the expression is a Callable, then it is required that the order of the operands returned by this function is the same as the order of arguments supplied to the corresponding call() method.

      Overrides:
      operands in class Expression
      Returns:
      an iterator containing the sub-expressions of this expression

    • getCollation

      public StringCollator getCollation()
      Get the collation used
      Returns:
      the collation

    • computeCardinality

      protected int computeCardinality()
      Compute the static cardinality of this expression
      Specified by:
      computeCardinality in class Expression
      Returns:
      the computed cardinality, as one of the values StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.EXACTLY_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_MORE

    • allowExtractingCommonSubexpressions

      public boolean allowExtractingCommonSubexpressions()
      Ask whether common subexpressions found in the operands of this expression can be extracted and evaluated outside the expression itself. The result is irrelevant in the case of operands evaluated with a different focus, which will never be extracted in this way, even if they have no focus dependency.
      Overrides:
      allowExtractingCommonSubexpressions in class Expression
      Returns:
      false for this kind of expression

    • copy

      public Expression copy(RebindingMap rebindings)
      Copy an expression. This makes a deep copy.
      Specified by:
      copy in class Expression
      Parameters:
      rebindings - variables that need to be re-bound
      Returns:
      the copy of the original expression

    • export

      public void export(ExpressionPresenter out) throws XPathException
      Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
      Specified by:
      export in interface ExportAgent
      Specified by:
      export in class Expression
      Parameters:
      out - the expression presenter used to display the structure
      Throws:
      XPathException - if the export fails, for example if an expression is found that won't work in the target environment.

    • getItemType

      public ItemType getItemType()
      Determine the data type of the expression, if possible. All expression return sequences, in general; this method determines the type of the items within the sequence, assuming that (a) this is known in advance, and (b) it is the same for all items in the sequence.

      This method should always return a result, though it may be the best approximation that is available at the time.

      Specified by:
      getItemType in class Expression
      Returns:
      a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)

    • unordered

      public Expression unordered(boolean retainAllNodes, boolean forStreaming) throws XPathException
      Replace this expression by a simpler expression that delivers the results without regard to order.
      Overrides:
      unordered in class Expression
      Parameters:
      retainAllNodes - set to true if the result must contain exactly the same nodes as the original; set to false if the result can eliminate (or introduce) duplicates.
      forStreaming - set to true if optimizing for streaming
      Returns:
      an expression that delivers the same nodes in a more convenient order
      Throws:
      XPathException - if the rewrite fails

    • 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.
      Overrides:
      evaluateItem in class Expression
      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

    • getIndex

      public int getIndex(AtomicMatchKey key)

    • 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 handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.
      Overrides:
      iterate in class Expression
      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

    • process

      public void process(Outputter output, XPathContext context) throws XPathException
      Process the instruction, without returning any tail calls
      Overrides:
      process in class Expression
      Parameters:
      output - the destination for the result
      context - The dynamic context, giving access to the current node,
      Throws:
      XPathException - if a dynamic error occurs

    • getImplementationMethod

      public int getImplementationMethod()
      Description copied from class: Expression
      An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.
      Specified by:
      getImplementationMethod in class Expression
      Returns:
      the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

    • getExpressionName

      public String getExpressionName()
      Get a name identifying the kind of expression, in terms meaningful to a user.
      Overrides:
      getExpressionName in class Expression
      Returns:
      a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in export() output displaying the expression.

    • getStreamerName

      public String getStreamerName()
      Description copied from class: Expression
      Get the (partial) name of a class that supports streaming of this kind of expression
      Overrides:
      getStreamerName in class Expression
      Returns:
      the partial name of a class that can be instantiated to provide streaming support in Saxon-EE, or null if there is no such class

    • getElaborator

      public Elaborator getElaborator()
      Make an elaborator for this expression
      Overrides:
      getElaborator in class Expression
      Returns:
      a suitable elaborator