net.sf.saxon.expr

Class IdentityComparison

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.BinaryExpression

net.sf.saxon.expr.IdentityComparison

All Implemented Interfaces:

Serializable, SourceLocator, LocationProvider, SaxonLocator, InstructionInfo, Locator

public final class IdentityComparison
extends BinaryExpression

IdentityComparison: a boolean expression that compares two nodes for equals, not-equals, greater-than or less-than based on identity and document ordering

See Also:

Serialized Form

Field Summary

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

operand0, operand1, operator

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

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, INHERITED_CONTEXT, INSPECTION_CONTEXT, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, NAVIGATION_CONTEXT, NODE_VALUE_CONTEXT, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, W3C_CONSUMING, W3C_FREE_RANGING, W3C_GROUP_CONSUMING, W3C_MOTIONLESS, WATCH_METHOD

Constructor Summary

Constructors

Constructor and Description
IdentityComparison(Expression p1, int op, Expression p2) Create an identity comparison identifying the two operands and the operator

Method Summary

Methods

Modifier and Type	Method and Description
Expression	copy() Copy an expression.
boolean	effectiveBooleanValue(XPathContext context) Get the effective boolean value of the expression.
BooleanValue	evaluateItem(XPathContext context) Evaluate the expression
ExpressionCompiler	getExpressionCompiler() Return the compiler of the IdentityComparison expression
ItemType	getItemType(TypeHierarchy th) Determine the data type of the expression
int	getStreamability(int syntacticContext, boolean allowExtensions, List<String> reasons) Get the "sweep" of this expression as defined in the W3C streamability specifications.
boolean	isGenerateIdEmulation() Test the flag that indicates different empty-sequence behavior when emulating comparison of two generate-id's
Expression	optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Perform optimisation of an expression and its subexpressions.
void	setGenerateIdEmulation(boolean flag) Set flag to indicate different empty-sequence behavior when emulating comparison of two generate-id's.
Expression	typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Type-check the expression

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

computeCardinality, computeSpecialProperties, displayOperator, equals, explain, explainExtraAttributes, getArguments, getOperands, getOperator, hashCode, isAssociative, isCommutative, isInverse, iterateSubExpressionInfo, iterateSubExpressions, promote, replaceSubExpression, setFlattened, simplify, toString

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

addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExecutable, getExpressionName, getHostLanguage, getImplementationMethod, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getStreamingAdjunct, getSystemId, getSystemId, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, iterateEvents, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setLocationId, staticTypeCheck, suppressValidation, toPattern, toStreamingPattern, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

IdentityComparison

public IdentityComparison(Expression p1,
                  int op,
                  Expression p2)

Create an identity comparison identifying the two operands and the operator

Parameters:

p1 - the left-hand operand

op - the operator, as a token returned by the Tokenizer (e.g. Token.LT)

p2 - the right-hand operand

Method Detail

setGenerateIdEmulation

public void setGenerateIdEmulation(boolean flag)

Set flag to indicate different empty-sequence behavior when emulating comparison of two generate-id's. This is relevant when operands evaluate to an empty sequence; if both are empty, the "is" operator returns (), while the generate-id() comparison compares two empty strings, which returns true; if one is empty, the "is" operator returns (), while the generate-id() comparison returns false.

Parameters:

flag - true if this function is being used to compare generate-id() output

isGenerateIdEmulation

public boolean isGenerateIdEmulation()

Test the flag that indicates different empty-sequence behavior when emulating comparison of two generate-id's

Returns:

true if this function is being used to compare generate-id() output

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                   ExpressionVisitor.ContextItemType contextItemType)
                     throws XPathException

Type-check the expression

Overrides:

typeCheck in class BinaryExpression

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,
                  ExpressionVisitor.ContextItemType contextItemType)
                    throws XPathException

Perform optimisation of an expression and its subexpressions.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

Overrides:

optimize in class BinaryExpression

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)

copy

public Expression copy()

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Returns:

the copy of the original expression

getStreamability

public int getStreamability(int syntacticContext,
                   boolean allowExtensions,
                   List<String> reasons)

Get the "sweep" of this expression as defined in the W3C streamability specifications. This provides an assessment of stylesheet code against the W3C criteria for guaranteed streamability, and is implemented to allow these criteria to be tested. It is not the case that all expression that emerge as streamable from this analysis are currently capable of being streamed by Saxon

Overrides:

getStreamability in class Expression

Parameters:

syntacticContext - one of the values Expression.NAVIGATION_CONTEXT, Expression.NODE_VALUE_CONTEXT, Expression.INHERITED_CONTEXT, Expression.INSPECTION_CONTEXT

allowExtensions - if false, the definition of "guaranteed streamability" in the W3C specification is used. If true, Saxon extensions are permitted, which make some

reasons - the caller may supply a list, in which case the implementation may add to this list a message explaining why the construct is not streamable, suitable for inclusion in an error message.

Returns:

one of the values Expression.W3C_MOTIONLESS, Expression.W3C_CONSUMING, Expression.W3C_GROUP_CONSUMING, Expression.W3C_FREE_RANGING

evaluateItem

public BooleanValue evaluateItem(XPathContext context)
                          throws XPathException

Evaluate the expression

Overrides:

evaluateItem in class Expression

Parameters:

context - 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

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
                              throws XPathException

Description copied from class: Expression

Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.

Overrides:

effectiveBooleanValue in class Expression

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the effective boolean value

Throws:

XPathException - if any dynamic error occurs evaluating the expression

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the data type of the expression

Specified by:

getItemType in class Expression

Parameters:

th - the type hierarchy cache

Returns:

Type.BOOLEAN

getExpressionCompiler

public ExpressionCompiler getExpressionCompiler()

Return the compiler of the IdentityComparison expression

Overrides:

getExpressionCompiler in class Expression

Returns:

the relevant ExpressionCompiler