net.sf.saxon.expr

Class VariableReference

java.lang.Object

net.sf.saxon.expr.ComputedExpression

net.sf.saxon.expr.VariableReference

All Implemented Interfaces:

java.io.Serializable, javax.xml.transform.SourceLocator, BindingReference, Container, Expression, InstructionInfoProvider

Direct Known Subclasses:

LocalVariableReference

public class VariableReference
extends ComputedExpression
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

Modifier and Type	Field and Description
(package private) Binding	binding
(package private) Value	constantValue
(package private) java.lang.String	displayName
(package private) SequenceType	staticType

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

locationId, staticProperties

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

Constructors

Constructor and Description
VariableReference()
VariableReference(VariableDeclaration declaration) Constructor

Method Summary

Modifier and Type	Method and Description
int	computeCardinality() Get the static cardinality
int	computeSpecialProperties() Determine the special properties of this expression
VariableReference	copy() Create a clone copy of this VariableReference
void	display(int level, java.io.PrintStream out, Configuration config) Diagnostic print of expression structure
boolean	equals(java.lang.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)
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
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
SequenceIterator	iterate(XPathContext c) Get the value of this variable in a given context.
Expression	optimize(Optimizer opt, StaticContext env, 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() Replace this VariableReference where appropriate by a more efficient implementation.
void	setStaticType(SequenceType type, Value value, int properties) Set static type.
Expression	typeCheck(StaticContext env, ItemType contextItemType) Type-check the expression.

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

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getInstructionInfo, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterateSubExpressions, markTailFunctionCalls, replaceSubExpression, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, simplify, suppressValidation, typeError

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Field Detail

binding

Binding binding

staticType

SequenceType staticType

constantValue

Value constantValue

displayName

transient java.lang.String displayName

Constructor Detail

VariableReference

public VariableReference()

VariableReference

public VariableReference(VariableDeclaration declaration)

Constructor

Parameters:

declaration - the variable declaration to which this variable refers

Method Detail

copy

public VariableReference copy()

Create a clone copy of this VariableReference

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

typeCheck

public Expression typeCheck(StaticContext env,
                            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

Specified by:

typeCheck in interface Expression

Parameters:

env - the static context of the expression

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:

StaticError - if an error is discovered during this phase (typically a type error)

XPathException

optimize

public Expression optimize(Optimizer opt,
                           StaticContext env,
                           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

Specified by:

optimize in interface Expression

Parameters:

opt - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.

env - the static context of the expression

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:

StaticError - if an error is discovered during this phase (typically a type error)

XPathException

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

refineVariableReference

public void refineVariableReference()

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

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the data type of the expression, if possible

Specified by:

getItemType in interface Expression

Parameters:

th -

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

Specified by:

computeCardinality in class ComputedExpression

computeSpecialProperties

public int computeSpecialProperties()

Determine the special properties of this expression

Overrides:

computeSpecialProperties in class ComputedExpression

Returns:

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

equals

public boolean equals(java.lang.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 java.lang.Object

hashCode

public int hashCode()

get HashCode for comparing two expressions

Overrides:

hashCode in class java.lang.Object

getIntrinsicDependencies

public int getIntrinsicDependencies()

Description copied from class: ComputedExpression

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 ComputedExpression

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

Specified by:

promote in interface Expression

Overrides:

promote in class ComputedExpression

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.

Specified by:

getImplementationMethod in interface Expression

Overrides:

getImplementationMethod in class ComputedExpression

iterate

public SequenceIterator iterate(XPathContext c)
                         throws XPathException

Get the value of this variable in a given context.

Specified by:

iterate in interface Expression

Overrides:

iterate in class ComputedExpression

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: ComputedExpression

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 Expression

Overrides:

evaluateItem in class ComputedExpression

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: ComputedExpression

Process the instruction, without returning any tail calls

Specified by:

process in interface Expression

Overrides:

process in class ComputedExpression

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

Throws:

XPathException

getBinding

public Binding getBinding()

Get the object bound to the variable

display

public void display(int level,
                    java.io.PrintStream out,
                    Configuration config)

Diagnostic print of expression structure

Specified by:

display in interface Expression

Parameters:

level - indentation level for this expression

out - Output destination