Package net.sf.saxon.expr
Class VariableReference
java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.VariableReference
- All Implemented Interfaces:
Serializable
,SourceLocator
,LocationProvider
,SaxonLocator
,BindingReference
,EvaluableItem
,SequenceIterable
,InstructionInfo
,Locator
- Direct Known Subclasses:
LocalVariableReference
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:
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Field Summary
FieldsFields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties
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Constructor Summary
ConstructorsConstructorDescriptionCreate a Variable ReferenceVariableReference
(Binding binding) Create a Variable Reference -
Method Summary
Modifier and TypeMethodDescriptionaddToPathMap
(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet) Add a representation of this expression to a PathMap.int
Get the static cardinalityint
Determine the special properties of this expressioncopy()
Create a clone copy of this VariableReferenceboolean
Test if this expression is the same as another expression.Evaluate an expression as a single item.Evaluate this variablevoid
explain
(ExpressionPresenter destination) Diagnostic print of expression structure.void
Fix up this variable reference to a Binding object, which enables the value of the variable to be located at run-time.Get the object bound to the variableGet the display name of the variable.int
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().int
Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions.Determine the data type of the expression, if possibleint
hashCode()
get HashCode for comparing two expressionsboolean
Determine whether this variable reference is filteredboolean
Test whether this variable reference is flattened - that is, whether it is atomized etcboolean
isInLoop()
Determine whether this variable reference appears in a loop relative to its declaration.Get the value of this variable in a given context.optimize
(ExpressionVisitor visitor, ItemType contextItemType) Type-check the expression.void
Process the instruction, without returning any tail callspromote
(PromotionOffer offer) Promote this expression if possiblevoid
refineVariableType
(ItemType type, int cardinality, Value constantValue, int properties, ExpressionVisitor visitor) Provide additional information about the type of the variable, typically derived by analyzing the initializer of the variable bindingvoid
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.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.typeCheck
(ExpressionVisitor visitor, ItemType contextItemType) Type-check the expression.Methods inherited from class net.sf.saxon.expr.Expression
adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, findParentOf, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, isUpdatingExpression, iterateEvents, iterateSubExpressions, markTailFunctionCalls, replaceSubExpression, resetLocalStaticProperties, setContainer, setLocationId, simplify, staticTypeCheck, suppressValidation, typeError
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Field Details
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binding
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staticType
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constantValue
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Constructor Details
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VariableReference
public VariableReference()Create a Variable Reference -
VariableReference
Create a Variable Reference- Parameters:
binding
- the variable binding to which this variable refers
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Method Details
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copy
Create a clone copy of this VariableReference- Specified by:
copy
in classExpression
- Returns:
- the cloned copy
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setStaticType
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 interfaceBindingReference
- Parameters:
type
- the static type of the variablevalue
- the value of the variable if this is a compile-time constantproperties
- static properties of the expression to which the variable is bound
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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 classExpression
- Parameters:
flattened
- set to true if the result of the expression is atomized or otherwise turned into an atomic value
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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
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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 classExpression
- Parameters:
filtered
- if true, marks this expression as the base of a filter expression
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isFiltered
public boolean isFiltered()Determine whether this variable reference is filtered- Returns:
- true if the value of the variable is filtered by a predicate
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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
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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 classExpression
- Parameters:
visitor
- an expression visitorcontextItemType
- 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 toType.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)
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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 classExpression
- Parameters:
visitor
- an expression visitorcontextItemType
- 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 toType.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)
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fixup
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 interfaceBindingReference
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refineVariableType
public void refineVariableType(ItemType type, int cardinality, Value constantValue, int properties, ExpressionVisitor visitor) 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 variablecardinality
- the cardinality of the variableconstantValue
- the actual value of the variable, if this is known statically, otherwise nullproperties
- additional static properties of the variable's initializervisitor
- an ExpressionVisitor
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getItemType
Determine the data type of the expression, if possible- Specified by:
getItemType
in classExpression
- 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)
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computeCardinality
public int computeCardinality()Get the static cardinality- Specified by:
computeCardinality
in classExpression
- 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
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computeSpecialProperties
public int computeSpecialProperties()Determine the special properties of this expression- Overrides:
computeSpecialProperties
in classExpression
- Returns:
StaticProperty.NON_CREATIVE
(unless the variable is assignable using saxon:assign)
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equals
Test if this expression is the same as another expression. (Note, we only compare expressions that have the same static and dynamic context). -
hashCode
public int hashCode()get HashCode for comparing two expressions -
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 classExpression
- Returns:
- a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty
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promote
Promote this expression if possible- Overrides:
promote
in classExpression
- 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
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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 classExpression
- Returns:
- the implementation method, for example
Expression.ITERATE_METHOD
orExpression.EVALUATE_METHOD
orExpression.PROCESS_METHOD
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addToPathMap
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 classExpression
- Parameters:
pathMap
- the PathMap to which the expression should be addedpathMapNodeSet
- 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.
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iterate
Get the value of this variable in a given context.- Specified by:
iterate
in interfaceSequenceIterable
- Overrides:
iterate
in classExpression
- 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
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evaluateItem
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 interfaceEvaluableItem
- Overrides:
evaluateItem
in classExpression
- 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
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process
Description copied from class:Expression
Process the instruction, without returning any tail calls- Overrides:
process
in classExpression
- Parameters:
c
- The dynamic context, giving access to the current node, the current variables, etc.- Throws:
XPathException
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evaluateVariable
Evaluate this variable- Parameters:
c
- the XPath dynamic context- Returns:
- the value of the variable
- Throws:
XPathException
- if any error occurs
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getBinding
Get the object bound to the variable- Returns:
- the Binding which declares this variable and associates it with a value
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getDisplayName
Get the display name of the variable. This is taken from the variable binding if possible- Returns:
- the display name (a lexical QName
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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 classExpression
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explain
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.- Specified by:
explain
in classExpression
- Parameters:
destination
- the expression presenter used to display the structure
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