Class IfExpression

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

public class IfExpression extends ComputedExpression implements TailCallReturner
An IfExpression returns the value of either the "then" part or the "else" part, depending on the value of the condition
See Also:
  • Constructor Details

  • Method Details

    • getCondition

      public Expression getCondition()
    • getThenExpression

      public Expression getThenExpression()
    • getElseExpression

      public Expression getElseExpression()
    • setCondition

      public void setCondition(Expression exp)
    • setThenExpression

      public void setThenExpression(Expression exp)
    • simplify

      public Expression simplify(StaticContext env) throws XPathException
      Simplify an expression
      Specified by:
      simplify in interface Expression
      Overrides:
      simplify in class ComputedExpression
      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
      Type-check the expression
      Specified by:
      typeCheck in interface Expression
      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.

      Specified by:
      optimize in interface Expression
      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
    • promote

      public Expression promote(PromotionOffer offer) throws XPathException
      Promote this expression if possible
      Specified by:
      promote in interface Expression
      Overrides:
      promote in class ComputedExpression
      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
      Returns:
      if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
      Throws:
      XPathException - if any error is detected
    • iterateSubExpressions

      public Iterator iterateSubExpressions()
      Get the immediate subexpressions of this expression
      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
    • suppressValidation

      public void suppressValidation(int validationMode)
      Suppress validation on contained element constructors, on the grounds that the parent element is already performing validation. The default implementation does nothing.
      Overrides:
      suppressValidation in class ComputedExpression
    • 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.
    • 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
    • evaluateItem

      public Item evaluateItem(XPathContext context) throws XPathException
      Evaluate the conditional expression in a given context
      Specified by:
      evaluateItem in interface Expression
      Overrides:
      evaluateItem in class ComputedExpression
      Parameters:
      context - the evaluation context
      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
      Iterate the path-expression in a given context
      Specified by:
      iterate in interface Expression
      Overrides:
      iterate in class ComputedExpression
      Parameters:
      context - the evaluation context
      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(XPathContext context) throws XPathException
      Process this expression as an instruction, writing results to the current receiver
      Specified by:
      process in interface Expression
      Overrides:
      process in class ComputedExpression
      Parameters:
      context - The dynamic context, giving access to the current node, the current variables, etc.
      Throws:
      XPathException
    • processLeavingTail

      public TailCall processLeavingTail(XPathContext context) throws XPathException
      ProcessLeavingTail: called to do the real work of this instruction. This method must be implemented in each subclass. The results of the instruction are written to the current Receiver, which can be obtained via the Controller.
      Specified by:
      processLeavingTail in interface TailCallReturner
      Parameters:
      context - The dynamic context of the transformation, giving access to the current node, the current variables, etc.
      Returns:
      null if the instruction has completed execution; or a TailCall indicating a function call or template call that is delegated to the caller, to be made after the stack has been unwound so as to save stack space.
      Throws:
      XPathException
    • getItemType

      public ItemType getItemType(TypeHierarchy th)
      Get data type of items in sequence returned by expression
      Specified by:
      getItemType in interface Expression
      Parameters:
      th -
      Returns:
      a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)
    • computeCardinality

      public int computeCardinality()
      Determine the static cardinality of the result
      Specified by:
      computeCardinality in class ComputedExpression
    • 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 ComputedExpression
    • display

      public void display(int level, PrintStream out, Configuration config)
      Diagnostic print of expression structure
      Specified by:
      display in interface Expression
      Parameters:
      level - indentation level for this expression
      out - Output destination
      config -