com.saxonica.extra
Class IndexedClosure

java.lang.Object
  net.sf.saxon.value.Value
      net.sf.saxon.value.Closure
          net.sf.saxon.value.MemoClosure
              com.saxonica.extra.IndexedClosure

All Implemented Interfaces:

Expression, java.io.Serializable, ValueRepresentation

public class IndexedClosure

extends MemoClosure

A subclass of MemoClosure that allows the construction of one or more indexes to provide rapid access to the items in the sequence.

There can be multiple indexes (a) because different expressions are used in filter predicates on this value, and (b) because of the problems of matching untyped atomic values. In an expression such as $seq[./A = $B], one index is built for each primitive type that occurs in the sequence $B. In this index, any untyped atomic values in ./A are converted to that primitive type. For an expression such as $seq[./A eq $B], a single index is built, in which untyped atomic values in ./A are converted to strings.

A particular difficulty arises where $B (in the expression $seq[./A eq $B]) is untypedAtomic. In this situation an index is built in which any untypedAtomic values in ./A are indexed as strings. While building the index, we note all the primitive types that occur in ./A, and then we convert the search term $B to each of these types in turn before doing the index lookup. In practice, of course, it is very rare for the index to be heterogeneous.

See Also:

Serialized Form

Nested Class Summary

Nested classes inherited from class net.sf.saxon.value.MemoClosure

MemoClosure.ProgressiveIterator

Field Summary

Fields inherited from class net.sf.saxon.value.MemoClosure

EMPTY, state

Fields inherited from class net.sf.saxon.value.Closure

depth, expression, inputIterator, savedXPathContext

Fields inherited from class net.sf.saxon.value.Value

EMPTY_CLASS_ARRAY

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Fields inherited from interface net.sf.saxon.om.ValueRepresentation

EMPTY_VALUE_ARRAY

Constructor Summary

IndexedClosure()

Method Summary

SequenceIterator	findItems(Expression use, SequenceIterator values, boolean convertUntypedToOther, AtomicComparer comparer, XPathContext context) Retrieve items that match a given index value
boolean	isIndexable() Determine wither this Closure is indexable
Value	materialize() Return a value containing all the items in the sequence returned by this SequenceIterator

Methods inherited from class net.sf.saxon.value.MemoClosure

getLength, isFullyRead, itemAt, iterate, process

Methods inherited from class net.sf.saxon.value.Closure

display, getCardinality, getImplementationMethod, getItemType, getSpecialProperties, make, makeIteratorClosure, reduce

Methods inherited from class net.sf.saxon.value.Value

asItem, asIterator, asValue, checkPermittedContents, convert, convertJavaObjectToXPath, convertToJava, effectiveBooleanValue, equals, evaluateAsString, evaluateItem, getDependencies, getIterator, getParentExpression, getStringValue, getStringValueCS, hashCode, iterateSubExpressions, makeQNameValue, optimize, promote, simplify, stringToNumber, toString, typeCheck

Methods inherited from class java.lang.Object

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

Constructor Detail

IndexedClosure

public IndexedClosure()

Method Detail

isIndexable

public boolean isIndexable()

Determine wither this Closure is indexable

Overrides:

isIndexable in class Closure

findItems

public SequenceIterator findItems(Expression use,
                                  SequenceIterator values,
                                  boolean convertUntypedToOther,
                                  AtomicComparer comparer,
                                  XPathContext context)
                           throws XPathException

Retrieve items that match a given index value

Parameters:

use - the expression whose value is to be matched

values - the set of values to be found

convertUntypedToOther - true if untypedAtomic values are to be converted to the type of the other operand

comparer - AtomicComparer used to compare values for equality (encapsulates a collation if necessary)

context - the dynamic evaluation context

Returns:

an iterator over the items that match the specified values

Throws:

XPathException

materialize

public Value materialize()
                  throws XPathException

Return a value containing all the items in the sequence returned by this SequenceIterator

Overrides:

materialize in class MemoClosure

Returns:

the corresponding value

Throws:

XPathException