net.sf.saxon.expr
Class VariableReference

java.lang.Object
  net.sf.saxon.expr.Expression
      net.sf.saxon.expr.VariableReference

All Implemented Interfaces:

Serializable, SourceLocator, BindingReference, EvaluableItem, SequenceIterable, InstructionInfoProvider

Direct Known Subclasses:

LocalVariableReference

public 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.

See Also:

Serialized Form

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

VariableReference()
Create a Variable Reference

VariableReference(Binding binding)
Create a Variable Reference

Method Summary

PathMap.PathMapNodeSet	addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet) Add a representation of this expression to a PathMap.
int	computeCardinality() Get the static cardinality
int	computeSpecialProperties() Determine the special properties of this expression
Expression	copy() Create a clone copy of this VariableReference
boolean	equals(Object other) Test if this expression is the same as another expression.
Item	evaluateItem(XPathContext c) Evaluate an expression as a single item.
ValueRepresentation	evaluateVariable(XPathContext c) Evaluate this variable
void	explain(ExpressionPresenter destination) Diagnostic print of expression structure.
void	fixup(Binding binding) Fix up this variable reference to a Binding object, which enables the value of the variable to be located at run-time.
Binding	getBinding() Get the object bound to the variable
String	getDisplayName() Get the display name of the variable.
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
int	getIntrinsicDependencies() Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions.
ItemType	getItemType(TypeHierarchy th) Determine the data type of the expression, if possible
int	hashCode() get HashCode for comparing two expressions
boolean	isFiltered() Determine whether this variable reference is filtered
boolean	isFlattened() Test whether this variable reference is flattened - that is, whether it is atomized etc
boolean	isInLoop() Determine whether this variable reference appears in a loop relative to its declaration.
SequenceIterator	iterate(XPathContext c) Get the value of this variable in a given context.
Expression	optimize(ExpressionVisitor visitor, ItemType contextItemType) Type-check the expression.
void	process(XPathContext c) Process the instruction, without returning any tail calls
Expression	promote(PromotionOffer offer) Promote this expression if possible
void	refineVariableReference(Expression parent) Replace this VariableReference where appropriate by a more efficient implementation.
void	refineVariableType(ItemType type, int cardinality, Value constantValue, int properties, ExpressionVisitor visitor)
void	setFiltered(boolean filtered) Mark an expression as filtered: that is, it appears as the base expression in a filter expression.
void	setFlattened(boolean flattened) Mark an expression as being "flattened".
void	setStaticType(SequenceType type, Value value, int properties) Set static type.
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.
Expression	typeCheck(ExpressionVisitor visitor, ItemType contextItemType) Type-check the expression.

Methods inherited from class net.sf.saxon.expr.Expression

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, effectiveBooleanValue, evaluateAsString, explain, findParentOf, getCardinality, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getInstructionInfo, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterateEvents, iterateSubExpressions, markTailFunctionCalls, replaceSubExpression, setContainer, setLocationId, simplify, staticTypeCheck, suppressValidation

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

VariableReference

public VariableReference()

Create a Variable Reference

VariableReference

public VariableReference(Binding binding)

Create a Variable Reference

Parameters:

binding - the variable binding to which this variable refers

Method Detail

copy

public Expression copy()

Create a clone copy of this VariableReference

Specified by:

copy in class Expression

Returns:

the cloned copy

setStaticType

public void setStaticType(SequenceType type,
                          Value 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

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()

Determine 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

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
                     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

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 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,
                           ItemType contextItemType)
                    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:

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 binding)

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

refineVariableType

public void refineVariableType(ItemType type,
                               int cardinality,
                               Value constantValue,
                               int properties,
                               ExpressionVisitor visitor)

refineVariableReference

public void refineVariableReference(Expression parent)

Replace this VariableReference where appropriate by a more efficient implementation. This can only be done after all slot numbers are allocated. The efficiency is gained by binding the VariableReference directly to a local or global slot, rather than going via the Binding object

Parameters:

parent - the parent expression of this variable reference

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the data type of the expression, if possible

Specified by:

getItemType in class Expression

Parameters:

th - the type hierarchy cache

Returns:

the type of the variable, if this can be determined statically; otherwise Type.ITEM (meaning not known in advance)

computeCardinality

public int computeCardinality()

Get the static cardinality

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

computeSpecialProperties

public int computeSpecialProperties()

Determine the special properties of this expression

Returns:

StaticProperty.NON_CREATIVE (unless the variable is assignable using saxon:assign)

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 Object

hashCode

public int hashCode()

get HashCode for comparing two expressions

Overrides:

hashCode in class Object

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:

a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException

Promote this expression if possible

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

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

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.

Overrides:

getImplementationMethod in class Expression

Returns:

the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

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.

Specified by:

iterate in interface SequenceIterable

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.

Specified by:

evaluateItem in interface EvaluableItem

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(XPathContext c)
             throws XPathException

Description copied from class: Expression

Process the instruction, without returning any tail calls

Overrides:

process in class Expression

Parameters:

c - The dynamic context, giving access to the current node, the current variables, etc.

Throws:

XPathException

evaluateVariable

public ValueRepresentation 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

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

explain

public void explain(ExpressionPresenter destination)

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

explain in class Expression

Parameters:

destination - the expression presenter used to display the structure