com.saxonica.ee.optim

Class IndexedFilterExpression

java.lang.Object

net.sf.saxon.expr.Expression

com.saxonica.ee.optim.IndexedFilterExpression

All Implemented Interfaces:

SourceLocator, ContextSwitchingExpression, IdentityComparable, InstructionInfo

public final class IndexedFilterExpression
extends Expression
implements ContextSwitchingExpression

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

Field Summary

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

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

Constructor Summary

Constructors

Constructor and Description
IndexedFilterExpression(VariableReference start, ComparisonExpression filter, boolean indexFirstOperand) Constructor

Method Summary

Methods

Modifier and Type	Method and Description
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.
Expression	getActionExpression() Get the subexpression that is evaluated in the new context
VariableReference	getBaseExpression() Get the underlying expression
ExpressionCompiler	getExpressionCompiler() Return the compiler of the IndexedFilter expression
ComparisonExpression	getFilter() Get the filter expression
ItemType	getItemType() Get the data type of the items returned
Expression	getSearchExpression() Get the expression whose value we will be searching for
Expression	getSelectExpression() Get the subexpression that sets the context item
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
Iterable<Operand>	operands() Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.
Expression	optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	promote(PromotionOffer offer, Expression parent) Promote this expression if possible
boolean	replaceOperand(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
Expression	typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Type-check the expression

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

addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, clearStreamabilityData, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getConfiguration, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExpressionName, getHostLanguage, getImplementationMethod, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLocationId, getObjectName, getPosture, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getStreamability, getStreamingAdjunct, getSweep, getSystemId, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isIdentical, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateEvents, makeStreamingAdjunct, markTailFunctionCalls, operandList, process, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, setPostureAndSweep, simplify, staticTypeCheck, suppressValidation, toPattern, toShortString, toStreamingPattern, toString, typeError, unordered

Methods inherited from class java.lang.Object

clone, finalize, 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()

Get the data type of the items returned

Specified by:

getItemType in class Expression

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

getSelectExpression

public Expression getSelectExpression()

Get the subexpression that sets the context item

Specified by:

getSelectExpression in interface ContextSwitchingExpression

Returns:

the subexpression that sets the context item, position, and size to each of its items in turn

getActionExpression

public Expression getActionExpression()

Get the subexpression that is evaluated in the new context

Specified by:

getActionExpression in interface ContextSwitchingExpression

Returns:

the subexpression evaluated in the context set by the controlling expression

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,
                   ContextItemStaticInfo contextInfo)
                     throws XPathException

Type-check the expression

Overrides:

typeCheck in class Expression

Parameters:

visitor - an expression visitor

contextInfo - information about the static type of the context item

Returns:

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

Throws:

XPathException - if an error is discovered during this phase (typically a type error)

optimize

public Expression optimize(ExpressionVisitor visitor,
                  ContextItemStaticInfo 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 - the parent expression

Returns:

the promoted expression (or the original expression, unchanged)

Throws:

XPathException - if any error is detected

operands

public Iterable<Operand> operands()

Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

Overrides:

operands in class Expression

Returns:

an iterator containing the sub-expressions of this expression

replaceOperand

public boolean replaceOperand(Expression original,
                     Expression replacement)

Replace one subexpression by a replacement subexpression

Overrides:

replaceOperand 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

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Iterate over the results, returning them in the correct order

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

getExpressionCompiler

public ExpressionCompiler getExpressionCompiler()

Return the compiler of the IndexedFilter expression

Overrides:

getExpressionCompiler in class Expression

Returns:

the relevant ExpressionCompiler

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