Package net.sf.saxon.expr

Class SlashExpression

  • All Implemented Interfaces:
    java.io.Serializable, javax.xml.transform.SourceLocator, LocationProvider, SaxonLocator, ContextMappingFunction<Item>, ContextSwitchingExpression, InstructionInfo, org.xml.sax.Locator
    Direct Known Subclasses:
    SimpleStepExpression
    public class SlashExpression
extends Expression
implements ContextSwitchingExpression, ContextMappingFunction<Item>
    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 ForEach instructions (when they return 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

        public void setStartExpression​(Expression start2)

      • setStepExpression

        public void setStepExpression​(Expression step2)

      • 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

      • getIntegerBounds

        public IntegerValue[] getIntegerBounds()
        For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis. The default implementation returns null, meaning "unknown" or "not applicable". Other implementations return an array of two IntegerValue objects, representing the lower and upper bounds respectively. The values UNBOUNDED_LOWER and UNBOUNDED_UPPER are used by convention to indicate that the value may be arbitrarily large. The values MAX_STRING_LENGTH and MAX_SEQUENCE_LENGTH are used to indicate values limited by the size of a string or the size of a sequence.
        Overrides:
        getIntegerBounds in class Expression
        Returns:
        the lower and upper bounds of integer values in the result, or null to indicate unknown or not applicable.

      • typeCheck

        public Expression typeCheck​(ExpressionVisitor visitor,
                            ExpressionVisitor.ContextItemType 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,
                           ExpressionVisitor.ContextItemType 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)

      • tryToMakeAbsolute

        public SlashExpression tryToMakeAbsolute​(TypeHierarchy th)
        Test whether a path expression is an absolute path - that is, a path whose first step selects a document node; if not, see if it can be converted to an absolute path. This is possible in cases where the path expression has the form a/b/c and it is known that the context item is a document node; in this case it is safe to change the path expression to /a/b/c
        Parameters:
        th - the type hierarchy cache
        Returns:
        the path expression if it is absolute; the converted path expression if it can be made absolute; or null if neither condition applies.

      • promoteFocusIndependentSubexpressions

        protected Expression promoteFocusIndependentSubexpressions​(ExpressionVisitor visitor,
                                                           ExpressionVisitor.ContextItemType 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 - if a static error is detected

      • promote

        public Expression promote​(PromotionOffer offer,
                          Expression parent)
                   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
        parent - the containing expression in the expression tree
        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<Expression> iterateSubExpressions()
        Get the immediate subexpressions of this expression
        Overrides:
        iterateSubExpressions in class Expression
        Returns:
        an iterator containing the sub-expressions of this expression

      • iterateSameFocusSubExpressions

        public java.util.Iterator<Expression> iterateSameFocusSubExpressions()
        Get the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression.
        Overrides:
        iterateSameFocusSubExpressions in class Expression
        Returns:
        an iterator containing those sub-expressions of this expression that are evaluated with the same focus as the parent 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

      • addToPathMap

        public PathMap.PathMapNodeSet addToPathMap​(PathMap pathMap,
                                           PathMap.PathMapNodeSet pathMapNodeSet)
        Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.
        Overrides:
        addToPathMap in class Expression
        Parameters:
        pathMap - the PathMap to which the expression should be added
        pathMapNodeSet -
        Returns:
        the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression

      • 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

      • iterate

        public SequenceIterator<? extends Item> iterate​(XPathContext context)
                                         throws XPathException
        Iterate the path-expression in a given context
        Overrides:
        iterate in class Expression
        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

      • map

        public 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<Item>
        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 - if a dynamic error is detected

      • 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

      • toString

        public java.lang.String toString()
        The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax
        Overrides:
        toString in class Expression
        Returns:
        a representation of the expression as a string

      • getFirstStep

        public Expression getFirstStep()
        Get the first step in this expression. A path expression A/B/C is represented as (A/B)/C, but the first step is A
        Returns:
        the first step in the expression, after expanding any nested path expressions

      • getStep

        public Expression getStep()
        Get step of the path expression
        Returns:
        the step expression

      • getRemainingSteps

        public Expression getRemainingSteps()
        Get all steps after the first. This is complicated by the fact that A/B/C is represented as ((A/B)/C; we are required to return B/C
        Returns:
        a path expression containing all steps in this path expression other than the first, after expanding any nested path expressions

      • getLastStep

        public Expression getLastStep()
        Get the last step of the path expression
        Returns:
        the last step in the expression, after expanding any nested path expressions

      • getLeadingSteps

        public Expression getLeadingSteps()
        Get a path expression consisting of all steps except the last
        Returns:
        a path expression containing all steps in this path expression other than the last, after expanding any nested path expressions

      • isAbsolute

        public boolean isAbsolute​(TypeHierarchy th)
        Test whether a path expression is an absolute path - that is, a path whose first step selects a document node
        Parameters:
        th - the type hierarchy cache
        Returns:
        true if the first step in this path expression selects a document node