Package net.sf.saxon.expr

Class SlashExpression

  • All Implemented Interfaces:
    ContextOriginator, ContextSwitchingExpression, ExportAgent, Locatable, IdentityComparable, Traceable
    Direct Known Subclasses:
    SimpleStepExpression
    public class SlashExpression
extends BinaryExpression
implements ContextSwitchingExpression
    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, wrapped in a documentSort() function to do the sorting and de-duplication required by the semantics of path expressions. The documentSort() is subsequently stripped off by the optimizer if sorting and deduplication is found to be unnecessary. The slash expression itself, therefore, does not perform sorting or de-duplication.

    • 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

      • getStart

        public Expression getStart()
        Get the left-hand operand
        Returns:
        the left-hand operand

      • setStart

        public void setStart​(Expression start)
        Set the left-hand operand
        Parameters:
        start - the left-hand operand

      • getStep

        public Expression getStep()
        Get the right-hand operand
        Returns:
        the right-hand operand

      • setStep

        public void setStep​(Expression step)
        Set the right-hand operand
        Parameters:
        step - the right-hand operand

      • getExpressionName

        public java.lang.String getExpressionName()
        Description copied from class: Expression
        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.

      • getItemType

        public final ItemType getItemType()
        Determine the data type of the items returned by this exprssion
        Specified by:
        getItemType in class Expression
        Returns:
        the type of the step

      • getStaticUType

        public UType getStaticUType​(UType contextItemType)
        Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.
        Overrides:
        getStaticUType in class Expression
        Parameters:
        contextItemType -
        Returns:
        the static item type of the expression according to the XSLT 3.0 defined rules

      • 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,
                            ContextItemStaticInfo contextInfo)
                     throws XPathException
        Type-check the expression
        Overrides:
        typeCheck in class BinaryExpression
        Parameters:
        visitor - an expression visitor
        contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.
        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,
                           ContextItemStaticInfo contextItemType)
                    throws XPathException
        Description copied from class: BinaryExpression
        Perform optimisation of an expression and its subexpressions.

        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 BinaryExpression
        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()
        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
        Returns:
        the path expression if it is absolute; the converted path expression if it can be made absolute; or null if neither condition applies.

      • getCost

        public double getCost()
        Return the estimated cost of evaluating an expression. This is a very crude measure based on the syntactic form of the expression (we have no knowledge of data values). We take the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one), and we assume that a sequence has length 5. The resulting estimates may be used, for example, to reorder the predicates in a filter expression so cheaper predicates are evaluated first.
        Overrides:
        getCost in class Expression
        Returns:
        the cost estimate

      • promoteFocusIndependentSubexpressions

        protected Expression promoteFocusIndependentSubexpressions​(ExpressionVisitor visitor,
                                                           ContextItemStaticInfo 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

      • 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

      • 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

      • copy

        public Expression copy​(RebindingMap rebindings)
        Copy an expression. This makes a deep copy.
        Specified by:
        copy in class Expression
        Parameters:
        rebindings -
        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 BinaryExpression
        Returns:
        StaticProperty.NO_NODES_NEWLY_CREATED. This is overridden for some subclasses.

      • isContextFree

        public boolean isContextFree()
        A SlashExpression is context free if the right-hand argument is an AxisExpression. This allows evaluation without creating a new XPathContext or FocusTrackingIterator; the expression can be evaluated as a simple flat-mapping function from nodes to nodes.
        Returns:
        true if the expression has been assessed as context-free, that is, if the right-hand operand is an AxisExpression

      • setContextFree

        public void setContextFree​(boolean free)
        Mark this expression as being context free (or not). This is done during reloading from a SEF file.
        Parameters:
        free - true if the expression has been assessed as context-free, that is, if the right-hand operand is an AxisExpression

      • equals

        public boolean equals​(java.lang.Object other)
        Is this expression the same as another expression?
        Overrides:
        equals in class BinaryExpression
        Parameters:
        other - the other operand; the result is false if this is not an Expression
        Returns:
        true if the other operand is an expression and if it can be determined that the two expressions are equivalent, in the sense that they will always return the same result.

      • computeHashCode

        public int computeHashCode()
        get HashCode for comparing two expressions
        Overrides:
        computeHashCode in class BinaryExpression
        Returns:
        a computed hash code

      • iterate

        public SequenceIterator 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

      • export

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

      • 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 BinaryExpression
        Returns:
        a representation of the expression as a string

      • toShortString

        public java.lang.String toShortString()
        Description copied from class: Expression
        Produce a short string identifying the expression for use in error messages
        Overrides:
        toShortString in class BinaryExpression
        Returns:
        a short string, sufficient to identify the expression

      • 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

      • 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()
        Test whether a path expression is an absolute path - that is, a path whose first step selects a document node
        Returns:
        true if the first step in this path expression selects a document node

      • getStreamerName

        public java.lang.String getStreamerName()
        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