Package net.sf.saxon.expr.instruct

Class ForEach

java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.instruct.Instruction
net.sf.saxon.expr.instruct.ForEach
All Implemented Interfaces:
ContextOriginator, ContextSwitchingExpression, ExportAgent, Locatable, IdentityComparable, Traceable
Direct Known Subclasses:
MultithreadedForEach
public class ForEach extends Instruction implements ContextSwitchingExpression
Handler for xsl:for-each elements in a stylesheet. The same class handles the "!" operator in XPath 3.0, which has identical semantics to xsl:for-each, and it is used to support the "/" operator in cases where it is known that the rhs delivers atomic values.

  • Field Details

    • containsTailCall

      protected boolean containsTailCall

    • selectOp

      protected Operand selectOp

    • actionOp

      protected Operand actionOp

    • separatorOp

      protected Operand separatorOp

    • threadsOp

      protected Operand threadsOp

    • _isInstruction

      protected boolean _isInstruction

  • Constructor Details

    • ForEach

      public ForEach(Expression select, Expression action)
      Create an xsl:for-each instruction
      Parameters:
      select - the select expression
      action - the body of the xsl:for-each loop

    • ForEach

      public ForEach(Expression select, Expression action, boolean containsTailCall, Expression threads)
      Create an xsl:for-each instruction
      Parameters:
      select - the select expression
      action - the body of the xsl:for-each loop
      containsTailCall - true if the body of the loop contains a tail call on the containing function
      threads - if >1 causes multithreaded execution (Saxon-EE only)

  • Method Details

    • setSeparatorExpression

      public void setSeparatorExpression(Expression separator)
      Set the separator expression (Saxon extension)
      Parameters:
      separator - the separator expression

    • getSeparatorExpression

      public Expression getSeparatorExpression()

    • setInstruction

      public void setInstruction(boolean inst)
      Say whether this ForEach expression originates as an XSLT instruction
      Parameters:
      inst - true if this is an xsl:for-each instruction; false if it is the XPath "!" operator

    • isInstruction

      public boolean isInstruction()
      Ask whether this expression is an instruction. In XSLT streamability analysis this is used to distinguish constructs corresponding to XSLT instructions from other constructs.
      Overrides:
      isInstruction in class Instruction
      Returns:
      true if this construct originates as an XSLT instruction

    • setContainsTailCall

      public void setContainsTailCall(boolean tc)
      Set whether this expression contains a call (on call-template or apply-templates) that is treated as a tail call because the select expression is known to be a singleton
      Parameters:
      tc - true if the action expression is to be treated as a tail call

    • isContainsTailCall

      public boolean isContainsTailCall()
      Ask whether this expression contains a call (on call-template or apply-templates) that is treated as a tail call because the select expression is known to be a singleton
      Returns:
      true if the action expression is to be treated as a tail call

    • getSelect

      public Expression getSelect()
      Get the select expression
      Returns:
      the select expression. Note this will have been wrapped in a sort expression if sorting was requested.

    • setSelect

      public void setSelect(Expression select)
      Set the select expression
      Parameters:
      select - the select expression of the for-each

    • getAction

      public Expression getAction()
      Get the action expression (in XSLT, the body of the xsl:for-each instruction
      Returns:
      the action expression

    • setAction

      public void setAction(Expression action)
      Set the action expression (in XSLT, the body of the xsl:for-each instruction)
      Parameters:
      action - the action expression

    • getThreads

      public Expression getThreads()
      Get the expression used to determine how many threads to use when multi-threading
      Returns:
      the saxon:threads expression if present, or null otherwise

    • setThreads

      public void setThreads(Expression threads)
      Set the expression used to determine how many threads to use when multi-threading
      Parameters:
      threads - the saxon:threads expression if present, or null otherwise

    • operands

      public Iterable<Operand> operands()
      Get the operands of this expression
      Specified by:
      operands in class Instruction
      Returns:
      the operands

    • getInstructionNameCode

      public int getInstructionNameCode()
      Get the name of this instruction for diagnostic and tracing purposes
      Overrides:
      getInstructionNameCode in class Instruction
      Returns:
      the code for name xsl:for-each

    • getSelectExpression

      public Expression getSelectExpression()
      Get the select expression
      Specified by:
      getSelectExpression in interface ContextSwitchingExpression
      Returns:
      the select expression. Note this will have been wrapped in a sort expression if sorting was requested.

    • setSelectExpression

      public void setSelectExpression(Expression select)
      Set the select expression
      Parameters:
      select - the select expression

    • setActionExpression

      public void setActionExpression(Expression action)
      Set the action expression
      Parameters:
      action - the select expression

    • getActionExpression

      public Expression getActionExpression()
      Get the subexpression that is evaluated in the new context
      Specified by:
      getActionExpression in interface ContextSwitchingExpression
      Returns:
      the subexpression evaluated in the context set by the controlling expression

    • getNumberOfThreadsExpression

      public Expression getNumberOfThreadsExpression()
      Get the number of threads requested
      Returns:
      the value of the saxon:threads attribute

    • getItemType

      public final ItemType getItemType()
      Determine the data type of the items returned by this expression
      Overrides:
      getItemType in class Instruction
      Returns:
      the data type

    • 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 - static type of the context item
      Returns:
      the static item type of the expression according to the XSLT 3.0 defined rules

    • mayCreateNewNodes

      public final boolean mayCreateNewNodes()
      Determine whether this instruction creates new nodes. This implementation returns true if the "action" creates new nodes. (Nodes created by the condition can't contribute to the result).
      Overrides:
      mayCreateNewNodes in class Instruction
      Returns:
      true if the instruction creates new nodes under some input conditions (or if it can't be proved that it doesn't)

    • typeCheck

      public Expression typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException
      Description copied from class: Expression
      Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

      This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

      This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.

      Overrides:
      typeCheck in class Expression
      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 contextInfo) 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
      contextInfo - 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)

    • 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.

      The default implementation of this method assumes that an expression does no navigation other than the navigation done by evaluating its subexpressions, and that the subexpressions are evaluated in the same context as the containing expression. The method must be overridden for any expression where these assumptions do not hold. For example, implementations exist for AxisExpression, ParentExpression, and RootExpression (because they perform navigation), and for the doc(), document(), and collection() functions because they create a new navigation root. Implementations also exist for PathExpression and FilterExpression because they have subexpressions that are evaluated in a different context from the calling expression.

      Overrides:
      addToPathMap in class Expression
      Parameters:
      pathMap - the PathMap to which the expression should be added
      pathMapNodeSet - the set of nodes in the path map that are affected
      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. For an expression that does navigation, it represents the end of the arc in the path map that describes the navigation route. For other expressions, it is the same as the input pathMapNode.

    • copy

      public Expression copy(RebindingMap rebindings)
      Copy an expression. This makes a deep copy.
      Specified by:
      copy in class Expression
      Parameters:
      rebindings - variables that need to be re-bound
      Returns:
      the copy of the original expression

    • computeSpecialProperties

      protected 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 Instruction
      Returns:
      a set of flags indicating static properties of this expression

    • alwaysCreatesNewNodes

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

    • isUpdatingExpression

      public boolean isUpdatingExpression()
      Determine whether this is an updating expression as defined in the XQuery update specification
      Overrides:
      isUpdatingExpression in class Expression
      Returns:
      true if this is an updating expression

    • checkForUpdatingSubexpressions

      public void checkForUpdatingSubexpressions() throws XPathException
      Check to ensure that this expression does not contain any inappropriate updating subexpressions. This check is overridden for those expressions that permit updating subexpressions.
      Overrides:
      checkForUpdatingSubexpressions in class Expression
      Throws:
      XPathException - if the expression has a non-permitted updating subexpression

    • 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 provided. This implementation provides both iterate() and process() methods natively.
      Overrides:
      getImplementationMethod in class Instruction
      Returns:
      the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

    • checkPermittedContents

      public void checkPermittedContents(SchemaType parentType, boolean whole) throws XPathException
      Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type. It's always OK to say yes, since the check will be repeated at run-time. The process of checking element and attribute constructors against the content model of a complex type also registers the type of content expected of those constructors, so the static validation can continue recursively.
      Overrides:
      checkPermittedContents in class Expression
      Parameters:
      parentType - the "given complex type": the method is checking that the nodes returned by this expression are acceptable members of the content model of this type
      whole - if true, we want to check that the value of this expression satisfies the content model as a whole; if false we want to check that the value of the expression is acceptable as one part of the content
      Throws:
      XPathException - if the value delivered by this expression cannot be part of the content model of the given type

    • makeSeparator

      protected NodeInfo makeSeparator(XPathContext context) throws XPathException
      Throws:
      XPathException

    • iterate

      public SequenceIterator iterate(XPathContext context) throws XPathException
      Return an Iterator to iterate over the values of the sequence.
      Overrides:
      iterate in class Instruction
      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

    • export

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

    • explainThreads

      protected void explainThreads(ExpressionPresenter out) throws XPathException
      Throws:
      XPathException

    • toString

      public String toString()

      The toString() method for an expression attempts to give a representation of the expression in an XPath-like form.

      For subclasses of Expression that represent XPath expressions, the result should always be a string that parses as an XPath 3.0 expression

      Overrides:
      toString in class Expression
      Returns:
      a representation of the expression as a string

    • toShortString

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

    • getExpressionName

      public String getExpressionName()
      Get a name identifying the kind of expression, in terms meaningful to a user.
      Overrides:
      getExpressionName in class Instruction
      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.

    • getStreamerName

      public 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

    • getElaborator

      public Elaborator getElaborator()
      Make an elaborator for this expression
      Overrides:
      getElaborator in class Expression
      Returns:
      a suitable elaborator