net.sf.saxon.expr

Class Atomizer

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.UnaryExpression

net.sf.saxon.expr.Atomizer

All Implemented Interfaces:

SourceLocator, IdentityComparable, InstructionInfo

public final class Atomizer
extends UnaryExpression

An Atomizer is an expression corresponding essentially to the fn:data() function: it maps a sequence by replacing nodes with their typed values

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Atomizer.AtomizingFunction Implement the mapping function.

Field Summary

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

operand

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
Atomizer(Expression sequence) Constructor

Method Summary

Methods

Modifier and Type	Method and Description
PathMap.PathMapNodeSet	addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet) Add a representation of this expression to a PathMap.
int	computeCardinality() Determine the static cardinality of the expression
int	computeSpecialProperties() Determine the special properties of this expression
Expression	copy() Copy an expression.
AtomicValue	evaluateItem(XPathContext context) Evaluate as an Item.
static ItemType	getAtomizedItemType(Expression operand, boolean alwaysUntyped, TypeHierarchy th) Compute the type that will result from atomizing the result of a given expression
static SequenceIterator	getAtomizingIterator(SequenceIterator base, boolean untyped) Get an iterator that returns the result of atomizing the sequence delivered by the supplied iterator
ExpressionCompiler	getExpressionCompiler() Return the compiler of the Atomizer expression
String	getExpressionName() Diagnostic print of expression structure.
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
ItemType	getItemType() Determine the data type of the items returned by the expression, if possible
ItemType	getOperandItemType(TypeHierarchy th)
protected OperandRole	getOperandRole() Get the usage (in terms of streamability analysis) of the single operand
AtomizerAdjunct	getStreamingAdjunct() Get a class that supports streamed evaluation of this expression
boolean	isUntyped() Ask whether it is known that any nodes in the input will always be untyped
SequenceIterator	iterate(XPathContext context) Iterate over the sequence of values
static Expression	makeAtomizer(Expression sequence) Make an atomizer with a given operand
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.
void	process(XPathContext context) Process the instruction, without returning any tail calls
Expression	simplify(ExpressionVisitor visitor) Simplify an expression
String	toShortString() Produce a short string identifying the expression for use in error messages
String	toString() The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.
Expression	typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Type-check the expression

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

displayOperator, equals, explain, getBaseExpression, hashCode, promote, replaceOperand

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

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

Methods inherited from class java.lang.Object

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

Constructor Detail

Atomizer

public Atomizer(Expression sequence)

Constructor

Parameters:

sequence - the sequence to be atomized

Method Detail

makeAtomizer

public static Expression makeAtomizer(Expression sequence)

Make an atomizer with a given operand

Parameters:

sequence - the operand

Returns:

an Atomizer that atomizes the given operand, or another expression that returns the same result

getOperandRole

protected OperandRole getOperandRole()

Description copied from class: UnaryExpression

Get the usage (in terms of streamability analysis) of the single operand

Specified by:

getOperandRole in class UnaryExpression

Returns:

the operand usage

getImplementationMethod

public int getImplementationMethod()

An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.

Overrides:

getImplementationMethod in class Expression

Returns:

the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

getOperandItemType

public ItemType getOperandItemType(TypeHierarchy th)

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException

Simplify an expression

Overrides:

simplify in class Expression

Parameters:

visitor - an expression visitor

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                   ContextItemStaticInfo contextInfo)
                     throws XPathException

Type-check the expression

Overrides:

typeCheck in class UnaryExpression

Parameters:

visitor - an expression visitor

contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.

Returns:

the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations

Throws:

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

optimize

public Expression optimize(ExpressionVisitor visitor,
                  ContextItemStaticInfo contextItemType)
                    throws XPathException

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 UnaryExpression

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

Throws:

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

isUntyped

public boolean isUntyped()

Ask whether it is known that any nodes in the input will always be untyped

Returns:

true if it is known that all nodes in the input will be untyped

computeSpecialProperties

public int computeSpecialProperties()

Determine the special properties of this expression

Overrides:

computeSpecialProperties in class UnaryExpression

Returns:

StaticProperty.NON_CREATIVE.

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

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 UnaryExpression

Returns:

an iterator containing the sub-expressions of this expression

getStreamingAdjunct

public AtomizerAdjunct getStreamingAdjunct()

Get a class that supports streamed evaluation of this expression

Overrides:

getStreamingAdjunct in class Expression

Returns:

the relevant StreamingAdjunct, or null if none is available

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Iterate over the sequence of values

Overrides:

iterate in class Expression

Parameters:

context - supplies the context for evaluation

Returns:

a SequenceIterator that can be used to iterate over the result of the expression

Throws:

XPathException - if any dynamic error occurs evaluating the expression

evaluateItem

public AtomicValue 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.

Overrides:

evaluateItem in class Expression

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

process

public void process(XPathContext context)
             throws XPathException

Process the instruction, without returning any tail calls

Overrides:

process in class Expression

Parameters:

context - The dynamic context, giving access to the current node, the current variables, etc.

Throws:

XPathException - if a dynamic error occurs

getItemType

public ItemType getItemType()

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

Overrides:

getItemType in class UnaryExpression

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.

getAtomizedItemType

public static ItemType getAtomizedItemType(Expression operand,
                           boolean alwaysUntyped,
                           TypeHierarchy th)

Compute the type that will result from atomizing the result of a given expression

Parameters:

operand - the given expression

alwaysUntyped - true if it is known that nodes will always be untyped

th - the type hierarchy cache

Returns:

the item type of the result of evaluating the operand expression, after atomization, or null if it is known that atomization will return an error

computeCardinality

public int computeCardinality()

Determine the static cardinality of the expression

Overrides:

computeCardinality in class UnaryExpression

Returns:

the computed cardinality, as one of the values StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.EXACTLY_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_MORE

addToPathMap

public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap,
                                  PathMap.PathMapNodeSet pathMapNodeSet)

Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.

The default implementation of this method assumes that an expression does no navigation other than the navigation done by evaluating its subexpressions, and that the subexpressions are evaluated in the same context as the containing expression. The method must be overridden for any expression where these assumptions do not hold. For example, implementations exist for AxisExpression, ParentExpression, and RootExpression (because they perform navigation), and for the doc(), document(), and collection() functions because they create a new navigation root. Implementations also exist for PathExpression and FilterExpression because they have subexpressions that are evaluated in a different context from the calling expression.

Overrides:

addToPathMap in class Expression

Parameters:

pathMap - the PathMap to which the expression should be added

pathMapNodeSet - the PathMapNodeSet to which the paths embodied in this expression should be added

Returns:

the pathMapNodeSet representing the points in the source document that are both reachable by this expression, and that represent possible results of this expression. For an expression that does navigation, it represents the end of the arc in the path map that describes the navigation route. For other expressions, it is the same as the input pathMapNode.

getAtomizingIterator

public static SequenceIterator getAtomizingIterator(SequenceIterator base,
                                    boolean untyped)
                                             throws XPathException

Get an iterator that returns the result of atomizing the sequence delivered by the supplied iterator

Parameters:

base - the supplied iterator, the input to atomization

untyped - this can safely be set to true if it is known that all nodes in the base sequence will be untyped; but it is always OK to set it to false.

Returns:

an iterator that returns atomic values, the result of the atomization

Throws:

XPathException - if a dynamic evaluation error occurs

getExpressionCompiler

public ExpressionCompiler getExpressionCompiler()

Return the compiler of the Atomizer expression

Overrides:

getExpressionCompiler in class Expression

Returns:

the relevant ExpressionCompiler

getExpressionName

public String getExpressionName()

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Overrides:

getExpressionName in class Expression

Returns:

a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.

toString

public String toString()

The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax

Overrides:

toString in class UnaryExpression

Returns:

a representation of the expression as a string

toShortString

public String toShortString()

Description copied from class: Expression

Produce a short string identifying the expression for use in error messages

Overrides:

toShortString in class UnaryExpression

Returns:

a short string, sufficient to identify the expression