net.sf.saxon.expr

Class VariableReference

Implemented Interfaces:
BindingReference, EvaluableItem, InstructionInfoProvider, SequenceIterable, Serializable, SourceLocator
Known Direct 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.

Field Summary

protected Binding
binding
protected SequenceType
staticType

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD, locationId, staticProperties

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

addToPathMap, adoptChildExpression, checkPermittedContents, computeCardinality, computeDependencies, computeSpecialProperties, computeStaticProperties, copy, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, explain, findParentOf, getCardinality, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getItemType, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterate, iterateEvents, iterateSubExpressions, markTailFunctionCalls, optimize, process, promote, replaceSubExpression, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toString, typeCheck, typeError

Field Details

binding

protected Binding binding

staticType

protected SequenceType staticType

Constructor Details

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 Details

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 interface 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.

computeCardinality

public int computeCardinality()
Get the static cardinality
Overrides:
computeCardinality in interface Expression

computeSpecialProperties

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

copy

public Expression copy()
Create a clone copy of this VariableReference
Overrides:
copy in interface Expression
Returns:
the cloned copy

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).

evaluateItem

public Item evaluateItem(XPathContext c)
            throws XPathException
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 interface Expression
Parameters:
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

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

explain

public void explain(ExpressionPresenter destination)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
Overrides:
explain in interface Expression

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

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

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 interface Expression

getIntrinsicDependencies

public int getIntrinsicDependencies()
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 interface Expression
Returns:
a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty

getItemType

public ItemType getItemType(TypeHierarchy th)
Determine the data type of the expression, if possible
Overrides:
getItemType in interface 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)

hashCode

public int hashCode()
get HashCode for comparing two expressions

isFiltered

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

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

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

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 interface 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

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 interface Expression

process

public void process(XPathContext c)
            throws XPathException
Process the instruction, without returning any tail calls
Overrides:
process in interface Expression
Parameters:

promote

public Expression promote(PromotionOffer offer)
            throws XPathException
Promote this expression if possible
Overrides:
promote in interface Expression

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

refineVariableType

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

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 interface Expression

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 interface Expression

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

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 interface Expression

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 interface Expression