Class SlashExpression

  • All Implemented Interfaces:
    java.io.Serializable, javax.xml.transform.SourceLocator, LocationProvider, SaxonLocator, ContextMappingFunction, EvaluableItem, SequenceIterable, InstructionInfo, org.xml.sax.Locator
    Direct Known Subclasses:
    AtomicMappingExpression, PathExpression

    public class SlashExpression
    extends Expression
    implements ContextMappingFunction
    A slash expression is any expression using the binary slash operator "/". The parser initially generates a slash expression for all occurrences of the binary "/" operator. Subsequently, as a result of type inferencing, the majority of slash expressions will be rewritten as instances of PathExpression (returning nodes) or AtomicMappingExpressions (returning atomic values). However, in the rare case where it is not possible to determine statically whether the rh operand returns nodes or atomic values, instances of this class may need to be interpreted directly at run time.
    See Also:
    Serialized Form
    • Constructor Detail

      • SlashExpression

        public SlashExpression​(Expression start,
                               Expression step)
        Constructor
        Parameters:
        start - The left hand operand (which must always select a sequence of nodes).
        step - The step to be followed from each node in the start expression to yield a new sequence; this may return either nodes or atomic values (but not a mixture of the two)
    • Method Detail

      • setStartExpression

        protected void setStartExpression​(Expression start2)
      • setStepExpression

        protected void setStepExpression​(Expression step2)
      • makeSlashExpression

        public static SlashExpression makeSlashExpression​(Expression start,
                                                          Expression step,
                                                          TypeHierarchy th)
        Static factory method, allowing early instantiation of a subclass if the type of the step expression is already known
      • getStartExpression

        public Expression getStartExpression()
        Get the start expression (the left-hand operand)
        Returns:
        the first operand
      • getStepExpression

        public Expression getStepExpression()
        Get the step expression (the right-hand operand)
        Returns:
        the second operand
      • isHybrid

        public boolean isHybrid()
        Determine whether this expression is capable (as far as static analysis is concerned) of returning a mixture of nodes and atomic values. If so, this needs to be prevented at run time
        Returns:
        true if the static type allows both nodes and atomic values
      • getItemType

        public final ItemType getItemType​(TypeHierarchy th)
        Determine the data type of the items returned by this exprssion
        Specified by:
        getItemType in class Expression
        Parameters:
        th - the type hierarchy cache
        Returns:
        the type of the step
      • typeCheck

        public Expression typeCheck​(ExpressionVisitor visitor,
                                    ItemType contextItemType)
                             throws XPathException
        Type-check the expression
        Overrides:
        typeCheck in class Expression
        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 Expression
        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)
      • promoteFocusIndependentSubexpressions

        protected Expression promoteFocusIndependentSubexpressions​(ExpressionVisitor visitor,
                                                                   ItemType contextItemType)
                                                            throws XPathException
        If any subexpressions within the step are not dependent on the focus, and if they are not "creative" expressions (expressions that can create new nodes), then promote them: this causes them to be evaluated once, outside the path expression
        Parameters:
        visitor - the expression visitor
        contextItemType - the type of the context item for evaluating the start expression
        Returns:
        the rewritten expression, or the original expression if no rewrite was possible
        Throws:
        XPathException
      • promote

        public Expression promote​(PromotionOffer offer)
                           throws XPathException
        Promote this expression if possible
        Overrides:
        promote in class Expression
        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 java.util.Iterator iterateSubExpressions()
        Get the immediate subexpressions of this expression
        Overrides:
        iterateSubExpressions in class Expression
        Returns:
        an iterator containing the sub-expressions of this expression
      • hasLoopingSubexpression

        public boolean hasLoopingSubexpression​(Expression child)
        Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
        Overrides:
        hasLoopingSubexpression in class Expression
        Parameters:
        child - the immediate subexpression
        Returns:
        true if the child expression is evaluated repeatedly
      • replaceSubExpression

        public boolean replaceSubExpression​(Expression original,
                                            Expression replacement)
        Replace one subexpression by a replacement subexpression
        Overrides:
        replaceSubExpression in class Expression
        Parameters:
        original - the original subexpression
        replacement - the replacement subexpression
        Returns:
        true if the original subexpression is found
      • computeDependencies

        public int computeDependencies()
        Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as XPathContext.VARIABLES and XPathContext.CURRENT_NODE
        Overrides:
        computeDependencies in class Expression
        Returns:
        the depencies, as a bit-mask
      • 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
      • 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 Expression
        Returns:
        the special properties, as a bit-significant integer
      • equals

        public boolean equals​(java.lang.Object other)
        Is this expression the same as another expression?
        Overrides:
        equals in class java.lang.Object
      • hashCode

        public int hashCode()
        get HashCode for comparing two expressions
        Overrides:
        hashCode in class java.lang.Object
      • map

        public final SequenceIterator map​(XPathContext context)
                                   throws XPathException
        Mapping function, from a node returned by the start iteration, to a sequence returned by the child.
        Specified by:
        map in interface ContextMappingFunction
        Parameters:
        context - The processing context. The item to be mapped is the context item identified from this context: the values of position() and last() also relate to the set of items being mapped
        Returns:
        a SequenceIterator over the sequence of items that the supplied input item maps to
        Throws:
        XPathException
      • explain

        public void explain​(ExpressionPresenter destination)
        Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
        Specified by:
        explain in class Expression
        Parameters:
        destination - the expression presenter used to display the structure