com.saxonica.expr
Class IndexedLookupExpression

java.lang.Object
  net.sf.saxon.expr.Expression
      com.saxonica.expr.IndexedLookupExpression

All Implemented Interfaces:

Serializable, SourceLocator, LocationProvider, SaxonLocator, InstructionInfo, Locator

public final class IndexedLookupExpression
extends Expression

An IndexedLookupExpression contains a base expression and a lookup expression. The base expression will always be a local variable reference. The expression returns true if the base expression (after atomization) contains the value of the lookup expression. That is, the expression is equivalent to exists(base[lookup]), except that lookup is evaluated with the same context as base.

See Also:

Serialized Form

Field Summary

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

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, WATCH_METHOD

Constructor Summary

IndexedLookupExpression(VariableReference base, Expression lookup, AtomicComparer comparer)
Constructor

Method Summary

int	computeCardinality() Get the static cardinality of this expression
int	computeDependencies() Determine which aspects of the context the expression depends on.
int	computeSpecialProperties() Get the static properties of this expression (other than its type).
Expression	copy() Copy an expression.
boolean	effectiveBooleanValue(XPathContext context) Get the effective boolean value of the expression.
boolean	equals(Object other) Is this expression the same as another expression?
Item	evaluateItem(XPathContext context) Evaluate an expression as a single item.
void	explain(ExpressionPresenter destination) Diagnostic print of expression structure.
AtomicComparer	getAtomicComparer() Get the atomic comparer used
VariableReference	getBaseExpression() Get the underlying expression
ItemType	getItemType(TypeHierarchy th) Get the data type of the items returned
Expression	getLookup() Get the lookup expression
Expression	getUseExpression() Get the expression that computes the key
int	hashCode() get HashCode for comparing two expressions
Iterator<Expression>	iterateSubExpressions() Get the immediate subexpressions of this expression
Expression	optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	promote(PromotionOffer offer, Expression parent) Promote this expression if possible
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
Expression	simplify(ExpressionVisitor visitor) Simplify an expression
Expression	typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Type-check the expression

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

addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, 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, getSystemId, getSystemId, hasLoopingSubexpression, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toString, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

IndexedLookupExpression

public IndexedLookupExpression(VariableReference base,
                               Expression lookup,
                               AtomicComparer comparer)

Constructor

Parameters:

base - A sequence expression denoting the sequence to be searched

lookup - An expression defining value to be sought

Method Detail

getItemType

public ItemType getItemType(TypeHierarchy th)

Get the data type of the items returned

Specified by:

getItemType in class Expression

Parameters:

th - the type hierarchy cache

Returns:

an integer representing the data type

getBaseExpression

public VariableReference getBaseExpression()

Get the underlying expression

Returns:

the expression being filtered

getLookup

public Expression getLookup()

Get the lookup expression

Returns:

the expression acting as the filter predicate

getUseExpression

public Expression getUseExpression()

Get the expression that computes the key

Returns:

the expression that computes the key

getAtomicComparer

public AtomicComparer getAtomicComparer()

Get the atomic comparer used

Returns:

the atomic comparer

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException

Simplify an expression

Overrides:

simplify in class Expression

Parameters:

visitor - an expression visitor

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

typeCheck

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

Type-check the expression

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 expression after type-checking (potentially modified to add run-time checks and/or conversions)

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ExpressionVisitor.ContextItemType contextItemType)

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 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

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

promote

public Expression promote(PromotionOffer offer,
                          Expression parent)
                   throws XPathException

Promote this expression if possible

Overrides:

promote in class Expression

Parameters:

offer - details of the promotion that is possible

parent -

Returns:

the promoted expression (or the original expression, unchanged)

Throws:

XPathException - if any error is detected

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()

Get the immediate subexpressions of this expression

Overrides:

iterateSubExpressions in class Expression

Returns:

the subexpressions, as an array

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)

Replace one subexpression by a replacement subexpression

Overrides:

replaceSubExpression in class Expression

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

computeCardinality

public int computeCardinality()

Get the static cardinality of this expression

Specified by:

computeCardinality in class Expression

Returns:

the cardinality. The method attempts to determine the case where the filter predicate is guaranteed to select at most one item from the sequence being filtered

computeSpecialProperties

public int computeSpecialProperties()

Get the static properties of this expression (other than its type). The result is bit-significant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

Overrides:

computeSpecialProperties in class Expression

Returns:

the static properties of the expression, as a bit-significant value

equals

public boolean equals(Object other)

Is this expression the same as another expression?

Overrides:

equals in class Object

Parameters:

other - the expression to be compared with this one

Returns:

true if the two expressions are statically equivalent

hashCode

public int hashCode()

get HashCode for comparing two expressions

Overrides:

hashCode in class Object

Returns:

the hash code

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

evaluateItem

public Item evaluateItem(XPathContext context)
                  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.

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

computeDependencies

public int computeDependencies()

Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as XPathContext.VARIABLES and XPathContext.CURRENT_NODE

Overrides:

computeDependencies in class Expression

Returns:

the dependencies

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