Class Instruction

java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.instruct.Instruction
All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, TailCallReturner, InstructionInfo, Locator
Direct Known Subclasses:
AnalyzeString, ApplyImports, ApplyTemplates, Block, CallTemplate, Choose, CopyOf, Doctype, ForEach, ForEachGroup, LocalParamBlock, LocalParamSetter, Message, ParentNodeConstructor, ProcessRegexMatchInstruction, ResultDocument, SimpleNodeConstructor, TraceExpression, UseAttributeSets
public abstract class Instruction extends Expression implements SourceLocator, TailCallReturner
Abstract superclass for all instructions in the compiled stylesheet. This represents a compiled instruction, and as such, the minimum information is retained from the original stylesheet.
Note: this class implements SourceLocator: that is, it can identify where in the stylesheet the source instruction was located.
See Also:

  • Constructor Details

    • Instruction

      public Instruction()
      Constructor

  • Method Details

    • getImplementationMethod

      public int getImplementationMethod()
      An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is prefered. For instructions this is the process() method.
      Overrides:
      getImplementationMethod in class Expression
      Returns:
      the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

    • 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

    • getInstructionName

      public String getInstructionName()
      Get a name identifying the kind of instruction, in terms meaningful to a user. This method is not used in the case where the instruction name code is a standard name (invalid input: '<'1024).
      Returns:
      a name identifying the kind of instruction, 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 instruction.

    • getExpressionName

      public 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(TypeHierarchy th)
      Get the item type of the items returned by evaluating this instruction
      Specified by:
      getItemType in class Expression
      Parameters:
      th - the type hierarchy cache
      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

    • processLeavingTail

      public abstract TailCall processLeavingTail(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:
      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(XPathContext context) throws XPathException
      Process the instruction, without returning any tail calls
      Overrides:
      process in class Expression
      Parameters:
      context - The dynamic context, giving access to the current node, the current variables, etc.
      Throws:
      XPathException - if a dynamic error occurs

    • getSourceLocator

      public 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(SourceLocator 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

    • simplify

      public abstract Expression simplify(ExpressionVisitor visitor) throws XPathException
      Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.
      Overrides:
      simplify in class Expression
      Parameters:
      visitor - an expression visitor
      Returns:
      the simplified expression
      Throws:
      XPathException - if an error is discovered during expression rewriting

    • 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

    • createsNewNodes

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

    • promoteInst

      protected void promoteInst(PromotionOffer offer) throws XPathException
      Handle promotion offers, that is, non-local tree rewrites.
      Parameters:
      offer - The type of rewrite being offered
      Throws:
      XPathException - if an error occurs

    • promote

      public Expression promote(PromotionOffer offer, Expression parent) throws XPathException
      Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. This method is always called at compile time.
      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 parent of the subexpression
      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

    • 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<? extends Item> 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

    • getIteratorFromProcessMethod

      protected final SequenceIterator<? extends Item> getIteratorFromProcessMethod(XPathContext context) throws XPathException
      Helper method to construct an iterator over the results of the expression when all that the expression itself offers is a process() method. This builds the entire results of the expression as a sequence in memory and then iterates over it.
      Parameters:
      context - the dynamic evaluation context
      Returns:
      an iterator over the results of the expression
      Throws:
      XPathException - if a dynamic error occurs

    • evaluateAsString

      public final 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
      ClassCastException - if the result type of the expression is not xs:string?

    • getConstructType

      public int getConstructType()
      Get the type of this expression for use in tracing and diagnostics
      Specified by:
      getConstructType in interface InstructionInfo
      Overrides:
      getConstructType in class Expression
      Returns:
      the type of expression, as enumerated in class Location

    • 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