com.saxonica.ee.optim

Class SwitchExpression

java.lang.Object

net.sf.saxon.expr.Expression

com.saxonica.ee.optim.SwitchExpression

All Implemented Interfaces:

ExportAgent, ConditionalInstruction, TailCallReturner, Locatable, IdentityComparable

public class SwitchExpression
extends Expression
implements TailCallReturner, ConditionalInstruction

An optimized Choose expression in which all the branches are tests of the same expression for equality with some value. Note this is not quite the same as the XQuery 3.1 switch expression; this switch expression is usually generated as the result of optimizing an xsl:choose or extended if/then/else expression.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	SwitchExpression.SwitchCaseInfo Data structure used for holding details of a switch expression

Field Summary

Fields

Modifier and Type	Field and Description
static OperandRole	SUBJECT

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

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_COST, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD

Constructor Summary

Constructors

Constructor and Description
SwitchExpression(SwitchExpression.SwitchCaseInfo switchCaseInfo) Create a switch expression

Method Summary

Modifier and Type	Method and Description
boolean	allowExtractingCommonSubexpressions() Ask whether common subexpressions found in the operands of this expression can be extracted and evaluated outside the expression itself.
protected int	computeCardinality() Compute the static cardinality of this expression
Expression	copy(RebindingMap rebindings) Copy an expression.
Item	evaluateItem(XPathContext context) Evaluate an expression as a single item.
void	export(ExpressionPresenter out) Diagnostic print of expression structure.
Operand	getAction(int index)
java.util.List<Operand>	getActions()
java.util.Map<AtomicMatchKey,java.lang.Integer>	getCaseMap() Get the map from XPathComparable objects representing the values to the expressions to be executed for each of these values
StringCollator	getCollation() Get the collation used
java.lang.String	getExpressionName() Get a name identifying the kind of expression, in terms meaningful to a user.
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 expression, if possible.
Expression	getOtherwiseExpression() Get the default ("otherwise") expression
Operand	getOtherwiseOperand()
java.lang.String	getStreamerName() Get the (partial) name of a class that supports streaming of this kind of expression
Expression	getSubjectExpression() Get the subject expression (the expression that computes the switch value)
boolean	isInstruction() Ask whether this expression is an instruction.
SequenceIterator<?>	iterate(XPathContext context) Return an Iterator to iterate over the values of a sequence.
java.lang.Iterable<Operand>	operands() Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.
void	process(XPathContext context) Process the instruction, without returning any tail calls
TailCall	processLeavingTail(XPathContext context) ProcessLeavingTail: called to do the real work of this instruction.
void	setInstruction(boolean inst) Say whether this switch expression originates as an XSLT instruction
Expression	unordered(boolean retainAllNodes, boolean forStreaming) Replace this expression by a simpler expression that delivers the results without regard to order.

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

addToPathMap, adoptChildExpression, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeHashCode, computeSpecialProperties, computeStaticProperties, dynamicError, effectiveBooleanValue, equals, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getConstructType, getCost, getDependencies, getEvaluationMethod, getExtraProperty, getIntegerBounds, getInterpretedExpression, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getStaticUType, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, markTailFunctionCalls, operandList, operandSparseList, optimize, optimizeChildren, prepareForStreaming, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, suppressValidation, toPattern, toShortString, toString, typeCheck, typeCheckChildren, typeError, verifyParentPointers

Methods inherited from class java.lang.Object

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

Field Detail

SUBJECT

public static final OperandRole SUBJECT

Constructor Detail

SwitchExpression

public SwitchExpression(SwitchExpression.SwitchCaseInfo switchCaseInfo)

Create a switch expression

Parameters:

switchCaseInfo - details of the expression to be constructed

Method Detail

setInstruction

public void setInstruction(boolean inst)

Say whether this switch expression originates as an XSLT instruction

Parameters:

inst - true if this started life as an xsl:choose instruction

isInstruction

public boolean isInstruction()

Ask whether this expression is an instruction. In XSLT streamability analysis this is used to distinguish constructs corresponding to XSLT instructions from other constructs.

Overrides:

isInstruction in class Expression

Returns:

true if this construct originates as an XSLT instruction

getSubjectExpression

public Expression getSubjectExpression()

Get the subject expression (the expression that computes the switch value)

Returns:

the expression that computes the switch value

getCaseMap

public java.util.Map<AtomicMatchKey,java.lang.Integer> getCaseMap()

Get the map from XPathComparable objects representing the values to the expressions to be executed for each of these values

Returns:

the map of case clauses

getOtherwiseExpression

public Expression getOtherwiseExpression()

Get the default ("otherwise") expression

Returns:

the "otherwise" expression giving the value to be returned if none of the cases match

getAction

public Operand getAction(int index)

getActions

public java.util.List<Operand> getActions()

getOtherwiseOperand

public Operand getOtherwiseOperand()

operands

public java.lang.Iterable<Operand> operands()

Description copied from class: Expression

Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation works off the results of iterateSubExpressions()

If the expression is a Callable, then it is required that the order of the operands returned by this function is the same as the order of arguments supplied to the corresponding call() method.

Overrides:

operands in class Expression

Returns:

an iterator containing the sub-expressions of this expression

getCollation

public StringCollator getCollation()

Get the collation used

Returns:

the collation

computeCardinality

protected int computeCardinality()

Compute the static cardinality of this expression

Specified by:

computeCardinality in class Expression

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

allowExtractingCommonSubexpressions

public boolean allowExtractingCommonSubexpressions()

Ask whether common subexpressions found in the operands of this expression can be extracted and evaluated outside the expression itself. The result is irrelevant in the case of operands evaluated with a different focus, which will never be extracted in this way, even if they have no focus dependency.

Overrides:

allowExtractingCommonSubexpressions in class Expression

Returns:

false for this kind of expression

copy

public Expression copy(RebindingMap rebindings)

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Parameters:

rebindings - variables that need to be re-bound

Returns:

the copy of the original expression

export

public void export(ExpressionPresenter out)
            throws XPathException

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

Specified by:

export in interface ExportAgent

Specified by:

export in class Expression

Parameters:

out - the expression presenter used to display the structure

Throws:

XPathException - if the export fails, for example if an expression is found that won't work in the target environment.

getItemType

public ItemType getItemType()

Determine the data type of the expression, if possible. All expression return sequences, in general; this method determines the type of the items within the sequence, assuming that (a) this is known in advance, and (b) it is the same for all items in the sequence.

This method should always return a result, though it may be the best approximation that is available at the time.

Specified by:

getItemType in class Expression

Returns:

a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)

unordered

public Expression unordered(boolean retainAllNodes,
                            boolean forStreaming)
                     throws XPathException

Replace this expression by a simpler expression that delivers the results without regard to order.

Overrides:

unordered in class Expression

Parameters:

retainAllNodes - set to true if the result must contain exactly the same nodes as the original; set to false if the result can eliminate (or introduce) duplicates.

forStreaming - set to true if optimizing for streaming

Returns:

an expression that delivers the same nodes in a more convenient order

Throws:

XPathException - if the rewrite fails

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.

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

iterate

public SequenceIterator<?> iterate(XPathContext context)
                            throws XPathException

Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.

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

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

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
                            throws XPathException

Description copied from interface: TailCallReturner

ProcessLeavingTail: called to do the real work of this instruction. This method must be implemented in each subclass. The results of the instruction are written to the current Receiver, which can be obtained via the Controller.

Specified by:

processLeavingTail in interface TailCallReturner

Parameters:

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

Returns:

null if the instruction has completed execution; or a TailCall indicating a function call or template call that is delegated to the caller, to be made after the stack has been unwound so as to save stack space.

Throws:

XPathException - if a dynamic error occurs during the evaluation of the instruction

getImplementationMethod

public int getImplementationMethod()

Description copied from class: Expression

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.

Specified by:

getImplementationMethod in class Expression

Returns:

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

getExpressionName

public java.lang.String getExpressionName()

Get a name identifying the kind of expression, in terms meaningful to a user.

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 export() output displaying the expression.

getStreamerName

public java.lang.String getStreamerName()

Description copied from class: Expression

Get the (partial) name of a class that supports streaming of this kind of expression

Overrides:

getStreamerName in class Expression

Returns:

the partial name of a class that can be instantiated to provide streaming support in Saxon-EE, or null if there is no such class