com.saxonica.extra
Class IndexedFilterExpression

java.lang.Object
  extended by net.sf.saxon.expr.Expression
      extended by com.saxonica.extra.IndexedFilterExpression
All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, ContextSwitchingExpression, EvaluableItem, SequenceIterable, InstructionInfo, Locator

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

See Also:
Serialized Form

Field Summary
 
Fields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties
 
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
 Expression getControlledExpression()
          Get the subexpression that is evaluated in the new context
 Expression getControllingExpression()
          Get the subexpression that sets the context item
 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
 boolean hasLoopingSubexpression(Expression child)
          Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
 SequenceIterator iterate(XPathContext context)
          Iterate over the results, returning them in the correct order
 Iterator<Expression> iterateSameFocusSubExpressions()
          Get the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression.
 Iterator<Expression> 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, Expression parent)
          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, checkForUpdatingSubexpressions, checkPermittedContents, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateEvents, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toString, typeError
 
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(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

getControllingExpression

public Expression getControllingExpression()
Get the subexpression that sets the context item

Specified by:
getControllingExpression in interface ContextSwitchingExpression
Returns:
the subexpression that sets the context item, position, and size to each of its items in turn

getControlledExpression

public Expression getControlledExpression()
Get the subexpression that is evaluated in the new context

Specified by:
getControlledExpression 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,
                            ItemType contextItemType)
                     throws XPathException
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)
Throws:
XPathException - if an error is discovered during this phase (typically a type error)

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,
                          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

iterateSameFocusSubExpressions

public Iterator<Expression> iterateSameFocusSubExpressions()
Get the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression.

Overrides:
iterateSameFocusSubExpressions in class Expression
Returns:
an iterator containing those sub-expressions of this expression that are evaluated with the same focus as the parent expression

hasLoopingSubexpression

public boolean hasLoopingSubexpression(Expression child)
Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly

Overrides:
hasLoopingSubexpression in class Expression
Parameters:
child - the immediate subexpression
Returns:
true if the child expression is evaluated repeatedly

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

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


Copyright (c) Saxonica Limited. All rights reserved.