net.sf.saxon.expr

Class SingletonAtomizer

java.lang.Object

net.sf.saxon.expr.ComputedExpression

net.sf.saxon.expr.UnaryExpression

net.sf.saxon.expr.SingletonAtomizer

All Implemented Interfaces:

java.io.Serializable, javax.xml.transform.SourceLocator, Container, Expression, InstructionInfoProvider

public final class SingletonAtomizer
extends UnaryExpression

A SingletonAtomizer combines the functions of an Atomizer and a CardinalityChecker: it is used to atomize a sequence of nodes, checking that the result of the atomization contains zero or one atomic values. Note that the input may be a sequence of nodes or atomic values, even though the result must contain at most one atomic value.

See Also:

Serialized Form

Field Summary

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

operand

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

locationId, staticProperties

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

Constructors

Constructor and Description
SingletonAtomizer(Expression sequence, RoleLocator role, boolean allowEmpty) Constructor

Method Summary

Modifier and Type	Method and Description
int	computeCardinality() Determine the static cardinality of the expression
int	computeSpecialProperties() Determine the special properties of this expression
protected java.lang.String	displayOperator(Configuration config) Give a string representation of the operator for use in diagnostics
Item	evaluateItem(XPathContext context) Evaluate as an Item.
ItemType	getItemType(TypeHierarchy th) Determine the data type of the items returned by the expression, if possible
RoleLocator	getRole() Get the RoleLocator (used to construct error messages)
Expression	simplify(StaticContext env) Simplify an expression
Expression	typeCheck(StaticContext env, ItemType contextItemType) Type-check the expression

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

display, equals, getBaseExpression, hashCode, iterateSubExpressions, optimize, promote, replaceSubExpression

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

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterate, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

SingletonAtomizer

public SingletonAtomizer(Expression sequence,
                         RoleLocator role,
                         boolean allowEmpty)

Constructor

Parameters:

sequence - the sequence to be atomized

allowEmpty - true if the result sequence is allowed to be empty.

Method Detail

simplify

public Expression simplify(StaticContext env)
                    throws XPathException

Simplify an expression

Specified by:

simplify in interface Expression

Overrides:

simplify in class UnaryExpression

Parameters:

env - the static context

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(StaticContext env,
                            ItemType contextItemType)
                     throws XPathException

Type-check the expression

Specified by:

typeCheck in interface Expression

Overrides:

typeCheck in class UnaryExpression

Parameters:

env - the static context of the expression

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 to perform necessary run-time type checks, and to perform other type-related optimizations

Throws:

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

XPathException

computeSpecialProperties

public int computeSpecialProperties()

Determine the special properties of this expression

Overrides:

computeSpecialProperties in class UnaryExpression

Returns:

StaticProperty.NON_CREATIVE.

getRole

public RoleLocator getRole()

Get the RoleLocator (used to construct error messages)

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate as an Item. This should only be called if the Atomizer has cardinality zero-or-one, which will only be the case if the underlying expression has cardinality zero-or-one.

Specified by:

evaluateItem in interface Expression

Overrides:

evaluateItem in class ComputedExpression

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence

Throws:

XPathException - if any dynamic error occurs evaluating the expression

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the data type of the items returned by the expression, if possible

Specified by:

getItemType in interface Expression

Overrides:

getItemType in class UnaryExpression

Parameters:

th -

Returns:

a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER. For this class, the result is always an atomic type, but it might be more specific.

computeCardinality

public int computeCardinality()

Determine the static cardinality of the expression

Overrides:

computeCardinality in class UnaryExpression

displayOperator

protected java.lang.String displayOperator(Configuration config)

Give a string representation of the operator for use in diagnostics

Specified by:

displayOperator in class UnaryExpression

Parameters:

config -

Returns:

the operator, as a string