com.saxonica.deploy
Class CompiledClosure

java.lang.Object
  net.sf.saxon.value.Value
      com.saxonica.deploy.CompiledClosure

All Implemented Interfaces:

Serializable, SequenceIterable, ValueRepresentation

Direct Known Subclasses:

CompiledMemoClosure

public class CompiledClosure
extends Value

A Closure represents a value that has not yet been evaluated: the value is represented by an expression, together with saved values of all the context variables that the expression depends on.

This Closure is designed for use when the value is only read once. If the value is read more than once, a new iterator over the underlying expression is obtained each time: this may (for example in the case of a filter expression) involve significant re-calculation.

The CompiledClosure class is similar to Closure, but is used only at run-time by queries that have been compiled into Java. It relies on the fact that Java provides a limited facility supporting closures: an anonymous inner class is allowed to reference local variables declared as "final", and these are automatically saved with the class instance so they are still available when the original stackframe disappears or changes. The code generator takes care to ensure that all variables that can be referenced from the inner class (specifically, those representing XPath variables as well as the context item) are held in variables that are declared final.

See Also:

Serialized Form

Field Summary

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

EMPTY_CLASS_ARRAY, INDETERMINATE_ORDERING

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

EMPTY_VALUE_ARRAY

Constructor Summary

CompiledClosure(SequenceIterator inputIterator, int primitiveType, int cardinality)
Create a compiled closure

Method Summary

int	getCardinality() Get the cardinality.
ItemType	getItemType(TypeHierarchy th) Get the static item type
int	getLength() Get the length of the value.
Comparable	getSchemaComparable() Get a Comparable value that implements the XML Schema ordering comparison semantics for this value.
SequenceIterator	iterate() Evaluate the expression in a given context to return an iterator over a sequence
Value	reduce() Reduce a value to its simplest form.

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

asItem, asItem, asIterator, asValue, checkPermittedContents, convertJavaObjectToXPath, convertToJava, convertToJava, effectiveBooleanValue, equals, fromItem, getCanonicalLexicalRepresentation, getIterator, getStringValue, getStringValueCS, itemAt, iterate, makeQNameValue, process, stringToNumber, toString

Methods inherited from class java.lang.Object

getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

CompiledClosure

public CompiledClosure(SequenceIterator inputIterator,
                       int primitiveType,
                       int cardinality)

Create a compiled closure

Parameters:

inputIterator - iterator over the values delivered by the expression

primitiveType - lowest-common primitive type of the items delivered by the iterator

cardinality - cardinality of the expression

Method Detail

getItemType

public ItemType getItemType(TypeHierarchy th)

Get the static item type

Overrides:

getItemType in class Value

Parameters:

th - the type hierarchy cache

Returns:

for the default implementation: AnyItemType (not known)

getCardinality

public int getCardinality()

Get the cardinality. This method is intended to be implemented in a subclass, but if it is not implemented, the fallback implementation simply returns StaticProperty.ALLOWS_ZERO_OR_MORE

Overrides:

getCardinality in class Value

Returns:

the cardinality

iterate

public SequenceIterator iterate()
                         throws XPathException

Evaluate the expression in a given context to return an iterator over a sequence

Specified by:

iterate in class Value

Returns:

an iterator over the sequence of items

Throws:

XPathException - if a dynamic error occurs. This is possible only in the case of values that are materialized lazily, that is, where the iterate() method leads to computation of an expression that delivers the values.

reduce

public Value reduce()
             throws XPathException

Reduce a value to its simplest form. If the value is a closure or some other form of deferred value such as a FunctionCallPackage, then it is reduced to a SequenceExtent. If it is a SequenceExtent containing a single item, then it is reduced to that item. One consequence that is exploited by class FilterExpression is that if the value is a singleton numeric value, then the result will be an instance of NumericValue

Overrides:

reduce in class Value

Returns:

the value in simplified form

Throws:

XPathException

getLength

public int getLength()
              throws XPathException

Get the length of the value. Note: this consumes the iterator!

Overrides:

getLength in class Value

Returns:

the number of items in the sequence

Throws:

XPathException

getSchemaComparable

public Comparable getSchemaComparable()

Get a Comparable value that implements the XML Schema ordering comparison semantics for this value. The default implementation returns "this", which ensures that comparisons between list values are handled by the equals() and compareTo() methods on this class itself. This is overridden for atomic values.

In the case of data types that are partially ordered, the returned Comparable extends the standard semantics of the compareTo() method by returning the value Value.INDETERMINATE_ORDERING when there is no defined order relationship between two given values.

Overrides:

getSchemaComparable in class Value

Returns:

a Comparable that follows XML Schema comparison rules