Package net.sf.saxon.expr

Class VariableReference

java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.VariableReference
All Implemented Interfaces:
BindingReference, ExportAgent, Locatable, IdentityComparable, Traceable
Direct Known Subclasses:
GlobalVariableReference, LocalVariableReference
public abstract class VariableReference extends Expression implements BindingReference
Variable reference: a reference to a variable. This may be an XSLT-defined variable, a range variable defined within the XPath expression, or a variable defined in some other static context.

  • Field Details

  • Constructor Details

    • VariableReference

      public VariableReference(StructuredQName name)
      Create a Variable Reference
      Parameters:
      name - the name of the variable

    • VariableReference

      public VariableReference(Binding binding)
      Create a Variable Reference
      Parameters:
      binding - the variable binding to which this variable refers

  • Method Details

    • setVariableName

      public void setVariableName(StructuredQName name)
      Set the variable name
      Parameters:
      name - the name of the variable

    • getVariableName

      public StructuredQName getVariableName()
      Get the variable name
      Returns:
      the name of the variable

    • copy

      public abstract Expression copy(RebindingMap rebindings)
      Create a clone copy of this VariableReference
      Specified by:
      copy in class Expression
      Parameters:
      rebindings - variables that need to switch to new bindings
      Returns:
      the cloned copy

    • getNetCost

      public int getNetCost()
      Description copied from class: Expression
      Return the net cost of evaluating this expression, excluding the cost of evaluating its operands. We take the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one).
      Overrides:
      getNetCost in class Expression
      Returns:
      the intrinsic cost of this operation, excluding the costs of evaluating the operands

    • copyFrom

      protected void copyFrom(VariableReference ref)

    • setStaticType

      public void setStaticType(SequenceType type, GroundedValue value, int properties)
      Set static type. This is a callback from the variable declaration object. As well as supplying the static type, it may also supply a compile-time value for the variable. As well as the type information, other static properties of the value are supplied: for example, whether the value is an ordered node-set.
      Specified by:
      setStaticType in interface BindingReference
      Parameters:
      type - the static type of the variable
      value - the value of the variable if this is a compile-time constant, or null otherwise
      properties - static properties of the expression to which the variable is bound

    • setFlattened

      public void setFlattened(boolean flattened)
      Mark an expression as being "flattened". This is a collective term that includes extracting the string value or typed value, or operations such as simple value construction that concatenate text nodes before atomizing. The implication of all of these is that although the expression might return nodes, the identity of the nodes has no significance. This is called during type checking of the parent expression. At present, only variable references take any notice of this notification.
      Overrides:
      setFlattened in class Expression
      Parameters:
      flattened - set to true if the result of the expression is atomized or otherwise turned into an atomic value

    • isFlattened

      public boolean isFlattened()
      Test whether this variable reference is flattened - that is, whether it is atomized etc
      Returns:
      true if the value of the variable is atomized, or converted to a string or number

    • setFiltered

      public void setFiltered(boolean filtered)
      Mark an expression as filtered: that is, it appears as the base expression in a filter expression. This notification currently has no effect except when the expression is a variable reference.
      Overrides:
      setFiltered in class Expression
      Parameters:
      filtered - if true, marks this expression as the base of a filter expression

    • isFiltered

      public boolean isFiltered()
      Determine whether this variable reference is filtered
      Returns:
      true if the value of the variable is filtered by a predicate

    • isInLoop

      public boolean isInLoop()
      Ask whether this variable reference appears in a loop relative to its declaration. By default, when in doubt, returns true. This is calculated during type-checking.
      Returns:
      true if this variable reference occurs in a loop, where the variable declaration is outside the loop

    • setInLoop

      public void setInLoop(boolean inLoop)
      Say whether this variable reference appears in a loop relative to its declaration.
      Parameters:
      inLoop - true if this variable reference occurs in a loop, where the variable declaration is outside the loop

    • typeCheck

      public Expression typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException
      Type-check the expression. At this stage details of the static type must be known. If the variable has a compile-time value, this is substituted for the variable reference
      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)

    • recomputeInLoop

      public void recomputeInLoop()

    • optimize

      public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) throws XPathException
      Optimize the expression. At this stage details of the static type must be known. If the variable has a compile-time value, this is substituted for the variable reference
      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)

    • fixup

      public void fixup(Binding newBinding)
      Fix up this variable reference to a Binding object, which enables the value of the variable to be located at run-time.
      Specified by:
      fixup in interface BindingReference
      Parameters:
      newBinding - the Binding to which the variable refers

    • refineVariableType

      public void refineVariableType(ItemType type, int cardinality, GroundedValue constantValue, int properties)
      Provide additional information about the type of the variable, typically derived by analyzing the initializer of the variable binding
      Parameters:
      type - the item type of the variable
      cardinality - the cardinality of the variable
      constantValue - the actual value of the variable, if this is known statically, otherwise null
      properties - additional static properties of the variable's initializer

    • getItemType

      public ItemType getItemType()
      Determine the data type of the expression, if possible
      Specified by:
      getItemType in class Expression
      Returns:
      the type of the variable, if this can be determined statically; otherwise 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 context item type
      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.

    • computeCardinality

      protected int computeCardinality()
      Get the static cardinality
      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.

    • computeSpecialProperties

      protected int computeSpecialProperties()
      Determine the special properties of this expression
      Overrides:
      computeSpecialProperties in class Expression
      Returns:
      StaticProperty.NO_NODES_NEWLY_CREATED (unless the variable is assignable using saxon:assign)

    • supportsLazyEvaluation

      public boolean supportsLazyEvaluation()
      Ask whether the expression supports lazy evaluation.
      Overrides:
      supportsLazyEvaluation in class Expression
      Returns:
      false either if the expression cannot be evaluated lazily because it has dependencies that cannot be saved in the context, or because lazy evaluation is pointless (for example, for literals and variable references).

    • equals

      public boolean equals(Object other)
      Test if this expression is the same as another expression. (Note, we only compare expressions that have the same static and dynamic context).
      Overrides:
      equals in class Expression
      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

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

    • getIntrinsicDependencies

      public int getIntrinsicDependencies()
      Description copied from class: Expression
      Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions. For example, position() has an intrinsic dependency on the context position, while (position()+1) does not. The default implementation of the method returns 0, indicating "no dependencies".
      Overrides:
      getIntrinsicDependencies in class Expression
      Returns:
      an integer containing bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty

    • 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 all three 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

    • getScopingExpression

      public Expression getScopingExpression()
      Get the innermost scoping expression of this expression, for expressions that directly depend on something in the dynamic context. For example, in the case of a local variable reference this is the expression that causes the relevant variable to be bound; for a context item expression it is the innermost focus-setting container. For expressions that have no intrinsic dependency on the dynamic context, the value returned is null; the scoping container for such an expression is the innermost scoping container of its operands.
      Overrides:
      getScopingExpression in class Expression
      Returns:
      the innermost scoping container of this expression

    • 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 PathMapNodeSet to which the paths embodied in this expression should be added
      Returns:
      the pathMapNodeSet representing the points in the source document that are both reachable by this expression, and that represent possible results of this 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.

    • iterate

      public SequenceIterator iterate(XPathContext c) throws XPathException
      Get the value of this variable in a given context.
      Overrides:
      iterate in class Expression
      Parameters:
      c - the XPathContext which contains the relevant variable bindings
      Returns:
      the value of the variable, if it is defined
      Throws:
      XPathException - if the variable is undefined

    • evaluateItem

      public Item evaluateItem(XPathContext c) throws XPathException
      Description copied from class: Expression
      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:
      c - 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

    • process

      public void process(Outputter output, XPathContext c) throws XPathException
      Description copied from class: Expression
      Process the instruction
      Overrides:
      process in class Expression
      Parameters:
      output - the destination for the result
      c - The dynamic context, giving access to the current node, the current variables, etc.
      Throws:
      XPathException - if a dynamic error occurs

    • evaluateVariable

      public Sequence evaluateVariable(XPathContext c) throws XPathException
      Evaluate this variable
      Parameters:
      c - the XPath dynamic context
      Returns:
      the value of the variable
      Throws:
      XPathException - if any error occurs

    • getBinding

      public Binding getBinding()
      Get the object bound to the variable
      Returns:
      the Binding which declares this variable and associates it with a value

    • getDisplayName

      public String getDisplayName()
      Get the display name of the variable. This is taken from the variable binding if possible
      Returns:
      the display name (a lexical QName

    • getEQName

      public String getEQName()
      Get the EQName of the variable. This is taken from the variable binding if possible. The returned name is in the format Q{uri}local if in a namespace, or the local name alone if not.
      Returns:
      the EQName, or the local name if not in a namespace

    • 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()
      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 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.

    • 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
      Specified by:
      export in class Expression
      Parameters:
      destination - 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.

    • 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