Package net.sf.saxon.expr

Class ForExpression

java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.Assignation
net.sf.saxon.expr.ForExpression
All Implemented Interfaces:
Binding, ExportAgent, LocalBinding, Locatable, IdentityComparable, Traceable
Direct Known Subclasses:
OuterForExpression
public class ForExpression extends Assignation
A ForExpression maps an expression over a sequence. We use a ForExpression in preference to a FLWORExpression to handle simple cases (roughly, the XPath subset). In 9.6, we no longer convert a FLWORExpression to a ForExpression if there is a position variable, which simplifies the cases this class has to handle.

  • Constructor Details

    • ForExpression

      public ForExpression()
      Create a "for" expression (for $x at $p in SEQUENCE return ACTION)

  • Method Details

    • 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.

    • typeCheck

      public Expression typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException
      Type-check the expression
      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)

    • getRangeVariableCardinality

      protected int getRangeVariableCardinality()
      Get the cardinality of the range variable
      Returns:
      the cardinality of the range variable (StaticProperty.EXACTLY_ONE). Can be overridden in a subclass

    • optimize

      public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) throws XPathException
      Optimize the expression
      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)

    • 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 Assignation
      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

    • 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.

    • 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

    • markTailFunctionCalls

      public int markTailFunctionCalls(StructuredQName qName, int arity)
      Mark tail function calls: only possible if the for expression iterates zero or one times. (This arises in XSLT/XPath, which does not have a LET expression, so FOR gets used instead)
      Overrides:
      markTailFunctionCalls in class Expression
      Parameters:
      qName - the name of the function
      arity - the arity (number of parameters) of the function
      Returns:
      UserFunctionCall.NOT_TAIL_CALL if no tail call was found; UserFunctionCall.FOREIGN_TAIL_CALL if a tail call on a different function was found; UserFunctionCall.SELF_TAIL_CALL if a tail recursive call was found and if this call accounts for the whole of the value.

    • isVacuousExpression

      public boolean isVacuousExpression()
      Determine whether this is a vacuous expression as defined in the XQuery update specification
      Overrides:
      isVacuousExpression in class Expression
      Returns:
      true if this expression is vacuous

    • 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.
      Specified by:
      getImplementationMethod in class Expression
      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

    • iterate

      public SequenceIterator iterate(XPathContext context) throws XPathException
      Iterate over the sequence of values
      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

    • process

      public void process(Outputter output, XPathContext context) throws XPathException
      Process this expression as an instruction, writing results to the current outputter
      Overrides:
      process in class Expression
      Parameters:
      output - the destination for the result
      context - The dynamic context, giving access to the current node, the current variables, etc.
      Throws:
      XPathException - if a dynamic error occurs

    • getItemType

      public ItemType getItemType()
      Determine the data type of the items returned by the expression, if possible
      Specified by:
      getItemType in class Expression
      Returns:
      one of the values Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known in advance)

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

    • computeCardinality

      protected int computeCardinality()
      Determine the static cardinality of the expression
      Specified by:
      computeCardinality in class Expression
      Returns:
      the computed cardinality, as one of the values StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.EXACTLY_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_MORE. May also return StaticProperty.ALLOWS_ZERO if the result is known to be an empty sequence, or StaticProperty.ALLOWS_MANY if if is known to return a sequence of length two or more.

    • toString

      public 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

    • 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

    • allowingEmptyString

      protected String allowingEmptyString()

    • 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.

    • explainSpecializedAttributes

      protected void explainSpecializedAttributes(ExpressionPresenter out)

    • getStreamerName

      public String getStreamerName()
      Description copied from class: Expression
      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