Package com.saxonica.ee.stream

Class StreamInstr

    • Method Detail

      • optimize

        public Expression optimize​(ExpressionVisitor visitor,
                           ContextItemStaticInfo contextItemType)
                    throws XPathException
        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 SourceDocument
        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)

      • mayCreateNewNodes

        public boolean mayCreateNewNodes()
        Determine whether this instruction creates new nodes. This implementation returns a default value of false
        Overrides:
        mayCreateNewNodes in class SourceDocument
        Returns:
        true if the instruction creates new nodes (or if it can't be proved that it doesn't)

      • computeDependencies

        public int computeDependencies()
        Compute the dependencies of an expression, as the union of the dependencies of its subexpressions. (This is overridden for path expressions and filter expressions, where the dependencies of a subexpression are not all propogated). This method should be called only once, to compute the dependencies; after that, getDependencies should be used.
        Overrides:
        computeDependencies in class SourceDocument
        Returns:
        the depencies, as a bit-mask

      • computeSpecialProperties

        protected 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 SourceDocument
        Returns:
        a set of flags indicating static properties of this expression

      • copy

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

      • push

        public void push​(Outputter output,
                 XPathContext context)
          throws XPathException
        Evaluate the instruction in push mode
        Specified by:
        push in interface Pusher
        Overrides:
        push in class SourceDocument
        Parameters:
        output - the final destination for the output of the instruction
        context - the evaluation context
        Throws:
        XPathException - in the event of a failure
        QuitParsingException - if there was an early exit, that is, if the instruction was evaluated without reading the input to completion

      • 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 implementation uses two threads: the instruction is evaluated in push mode in a child thread (using the process() method), putting its results on a queue, from which this method reads them.
        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