Class Instruction

    • Constructor Detail

      • Instruction

        public Instruction()
        Constructor
    • Method Detail

      • isInstruction

        public boolean isInstruction()
        Description copied from class: Expression
        Ask whether this expression is an instruction. In XSLT streamability analysis this is used to distinguish constructs corresponding to XSLT instructions from other constructs, typically XPath expressions (but also things like attribute constructors on a literal result element, references to attribute sets, etc. However, an XPath expression within a text value template in a text node of an XSLT stylesheet is treated as an instruction. In a non-XSLT environment (such as XQuery) this property has no meaning and its setting is undefined.
        Overrides:
        isInstruction in class Expression
        Returns:
        true if this construct originates as an XSLT instruction
      • getInstructionNameCode

        public int getInstructionNameCode()
        Get the namecode of the instruction for use in diagnostics
        Returns:
        a code identifying the instruction: typically but not always the fingerprint of a name in the XSLT namespace
      • getExpressionName

        public java.lang.String getExpressionName()
        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 explain() output displaying the expression.
      • getItemType

        public ItemType getItemType()
        Get the item type of the items returned by evaluating this instruction
        Specified by:
        getItemType in class Expression
        Returns:
        the static item type of the instruction
      • computeCardinality

        public int computeCardinality()
        Get the cardinality of the sequence returned by evaluating this instruction
        Specified by:
        computeCardinality in class Expression
        Returns:
        the static cardinality
      • operands

        public abstract java.lang.Iterable<Operand> operands()
        Description copied from class: Expression
        Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation works off the results of iterateSubExpressions()

        If the expression is a Callable, then it is required that the order of the operands returned by this function is the same as the order of arguments supplied to the corresponding call() method.

        Overrides:
        operands in class Expression
        Returns:
        an iterator containing the sub-expressions of this expression
      • processLeavingTail

        public abstract TailCall processLeavingTail​(Outputter output,
                                                    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:
        output - the destination for the result
        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 - if a dynamic error occurs during the evaluation of the instruction
      • process

        public void process​(Outputter output,
                            XPathContext context)
                     throws XPathException
        Process the instruction, without returning any tail calls
        Overrides:
        process in class Expression
        Parameters:
        output - the destination for the result
        context - The dynamic context, giving access to the current node,
        Throws:
        XPathException - if a dynamic error occurs
      • getSourceLocator

        public javax.xml.transform.SourceLocator getSourceLocator()
        Get a SourceLocator identifying the location of this instruction
        Returns:
        the location of this instruction in the source stylesheet or query
      • dynamicError

        protected static XPathException dynamicError​(Location loc,
                                                     XPathException error,
                                                     XPathContext context)
        Construct an exception with diagnostic information. Note that this method returns the exception, it does not throw it: that is up to the caller.
        Parameters:
        loc - the location of the error
        error - The exception containing information about the error
        context - The controller of the transformation
        Returns:
        an exception based on the supplied exception, but with location information added relating to this instruction
      • assembleParams

        public static ParameterSet assembleParams​(XPathContext context,
                                                  WithParam[] actualParams)
                                           throws XPathException
        Assemble a ParameterSet. Method used by instructions that have xsl:with-param children. This method is used for the non-tunnel parameters.
        Parameters:
        context - the XPath dynamic context
        actualParams - the set of with-param parameters that specify tunnel="no"
        Returns:
        a ParameterSet
        Throws:
        XPathException - if an error occurs evaluating one of the parameters
      • assembleTunnelParams

        public static ParameterSet assembleTunnelParams​(XPathContext context,
                                                        WithParam[] actualParams)
                                                 throws XPathException
        Assemble a ParameterSet. Method used by instructions that have xsl:with-param children. This method is used for the tunnel parameters.
        Parameters:
        context - the XPath dynamic context
        actualParams - the set of with-param parameters that specify tunnel="yes"
        Returns:
        a ParameterSet
        Throws:
        XPathException - if an error occurs evaluating one of the tunnel parameters
      • 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:
        a set of flags indicating static properties of this expression
      • getNetCost

        public int getNetCost()
        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:
        getNetCost in class Expression
        Returns:
        the intrinsic cost of this operation, excluding the costs of evaluating the operands
      • mayCreateNewNodes

        public boolean mayCreateNewNodes()
        Ask whether this instruction potentially creates and returns new nodes. Returns true if some branches or dynamic conditions result in new nodes being created. This implementation returns a default value of false
        Returns:
        true if the instruction creates new nodes under some input conditions (or if it can't be proved that it doesn't)
      • alwaysCreatesNewNodes

        public boolean alwaysCreatesNewNodes()
        Ask whether it is guaranteed that every item in the result of this instruction is a newly created node.
        Returns:
        true if result of the instruction is always either an empty sequence or a sequence consisting entirely of newly created nodes
      • someOperandCreatesNewNodes

        protected final boolean someOperandCreatesNewNodes()
        Helper method for mayCreateNewNodes() - returns true if any operand creates new nodes
        Returns:
        true if any operand creates new nodes
      • evaluateItem

        public Item evaluateItem​(XPathContext context)
                          throws XPathException
        Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.
        Overrides:
        evaluateItem in class Expression
        Parameters:
        context - The context in which the expression is to be evaluated
        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
        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 default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.
        Overrides:
        iterate in class Expression
        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
      • evaluateAsString

        public final java.lang.CharSequence evaluateAsString​(XPathContext context)
                                                      throws XPathException
        Evaluate an expression as a String. This function must only be called in contexts where it is known that the expression will return a single string (or where an empty sequence is to be treated as a zero-length string). Implementations should not attempt to convert the result to a string, other than converting () to "". This method is used mainly to evaluate expressions produced by compiling an attribute value template.
        Overrides:
        evaluateAsString in class Expression
        Parameters:
        context - The context in which the expression is to be evaluated
        Returns:
        the value of the expression, evaluated in the current context. The expression must return a string or (); if the value of the expression is (), this method returns "".
        Throws:
        XPathException - if any dynamic error occurs evaluating the expression
        java.lang.ClassCastException - if the result type of the expression is not xs:string?
      • isXSLT

        public boolean isXSLT()
        Establish whether this is an XSLT instruction or an XQuery instruction (used to produce appropriate diagnostics)
        Returns:
        true for XSLT, false for XQuery