com.saxonica.extra
Class IndexedFilterExpression

java.lang.Object
  net.sf.saxon.expr.Expression
      com.saxonica.extra.IndexedFilterExpression

All Implemented Interfaces:

Serializable, SourceLocator, EvaluableItem, SequenceIterable, InstructionInfoProvider

public final class IndexedFilterExpression
extends Expression

An IndexedFilterExpression contains a base expression and a filter predicate. The base expression will always be a local variable reference. The filter will always be a Comparison, and it will have no positional dependencies

See Also:

Serialized Form

Field Summary

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

IndexedFilterExpression(VariableReference start, ComparisonExpression filter, boolean indexFirstOperand)
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	equals(Object other) Is this expression the same as another expression?
void	explain(ExpressionPresenter out) Diagnostic print of expression structure.
VariableReference	getBaseExpression() Get the underlying expression
ComparisonExpression	getFilter() Get the filter expression
ItemType	getItemType(TypeHierarchy th) Get the data type of the items returned
Expression	getSearchExpression() Get the expression whose value we will be searching for
Expression	getUseExpression() Get the expression to be indexed
int	hashCode() get HashCode for comparing two expressions
SequenceIterator	iterate(XPathContext context) Iterate over the results, returning them in the correct order
Iterator	iterateSubExpressions() Get the immediate subexpressions of this expression
Expression	optimize(ExpressionVisitor visitor, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	promote(PromotionOffer offer) Promote this expression if possible
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
Expression	typeCheck(ExpressionVisitor visitor, ItemType contextItemType) Type-check the expression

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

addToPathMap, adoptChildExpression, checkPermittedContents, computeStaticProperties, display, doPromotion, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, findParentOf, getCardinality, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterateEvents, markTailFunctionCalls, process, setContainer, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toString

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

IndexedFilterExpression

public IndexedFilterExpression(VariableReference start,
                               ComparisonExpression filter,
                               boolean indexFirstOperand)

Constructor

Parameters:

start - Variable containing the sequence of items from which the selection will take place.

filter - An expression defining the filter predicate

indexFirstOperand - true if the first operand of the filter comparison is to be indexed, false if the second operand is to be indexed

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

getFilter

public ComparisonExpression getFilter()

Get the filter expression

Returns:

the expression acting as the filter predicate

getUseExpression

public Expression getUseExpression()

Get the expression to be indexed

Returns:

the "use" expression, the expression that computes the index key for each item in the population

getSearchExpression

public Expression getSearchExpression()

Get the expression whose value we will be searching for

Returns:

the search expression

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType 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,
                           ItemType 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)
                   throws XPathException

Promote this expression if possible

Overrides:

promote in class Expression

Parameters:

offer - details of the promotion that is possible

Returns:

the promoted expression (or the original expression, unchanged)

Throws:

XPathException - if any error is detected

iterateSubExpressions

public Iterator 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

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.

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

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Iterate over the results, returning them in the correct order

Specified by:

iterate in interface SequenceIterable

Overrides:

iterate in class Expression

Parameters:

context - the dynamic context for the evaluation

Returns:

an iterator over the expression results

Throws:

XPathException - if any dynamic error occurs

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 out)

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

explain in class Expression

Parameters:

out - the expression presenter used to display the structure