net.sf.saxon.expr

Class IfExpression

java.lang.Object

net.sf.saxon.expr.ComputedExpression

net.sf.saxon.expr.IfExpression

All Implemented Interfaces:

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

public class IfExpression
extends ComputedExpression
implements TailCallReturner

An IfExpression returns the value of either the "then" part or the "else" part, depending on the value of the condition

See Also:

Serialized Form

Field Summary

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
IfExpression(Expression condition, Expression thenExp, Expression elseExp) Constructor

Method Summary

Modifier and Type	Method and Description
void	checkPermittedContents(SchemaType parentType, StaticContext env, boolean whole) Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type.
int	computeCardinality() Determine the static cardinality of the result
int	computeSpecialProperties() Get the static properties of this expression (other than its type).
void	display(int level, java.io.PrintStream out, Configuration config) Diagnostic print of expression structure
Item	evaluateItem(XPathContext context) Evaluate the conditional expression in a given context
Expression	getCondition()
Expression	getElseExpression()
ItemType	getItemType(TypeHierarchy th) Get data type of items in sequence returned by expression
Expression	getThenExpression()
SequenceIterator	iterate(XPathContext context) Iterate the path-expression in a given context
java.util.Iterator	iterateSubExpressions() Get the immediate subexpressions of this expression
boolean	markTailFunctionCalls(int nameCode, int arity) Mark tail calls on used-defined functions.
Expression	optimize(Optimizer opt, StaticContext env, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
void	process(XPathContext context) Process this expression as an instruction, writing results to the current receiver
TailCall	processLeavingTail(XPathContext context) ProcessLeavingTail: called to do the real work of this instruction.
Expression	promote(PromotionOffer offer) Promote this expression if possible
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
void	setCondition(Expression exp)
void	setThenExpression(Expression exp)
Expression	simplify(StaticContext env) Simplify an expression
void	suppressValidation(int validationMode) Suppress validation on contained element constructors, on the grounds that the parent element is already performing validation.
Expression	typeCheck(StaticContext env, ItemType contextItemType) Type-check the expression

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

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

Methods inherited from class java.lang.Object

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

Constructor Detail

IfExpression

public IfExpression(Expression condition,
                    Expression thenExp,
                    Expression elseExp)

Constructor

Method Detail

getCondition

public Expression getCondition()

getThenExpression

public Expression getThenExpression()

getElseExpression

public Expression getElseExpression()

setCondition

public void setCondition(Expression exp)

setThenExpression

public void setThenExpression(Expression exp)

simplify

public Expression simplify(StaticContext env)
                    throws XPathException

Simplify an expression

Specified by:

simplify in interface Expression

Overrides:

simplify in class ComputedExpression

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

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

optimize

public Expression optimize(Optimizer opt,
                           StaticContext env,
                           ItemType contextItemType)
                    throws XPathException

Description copied from interface: Expression

Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.

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.

Specified by:

optimize in interface Expression

Parameters:

opt - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.

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 if appropriate to optimize execution

Throws:

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

XPathException

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException

Promote this expression if possible

Specified by:

promote in interface Expression

Overrides:

promote in class ComputedExpression

Parameters:

offer - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression

Returns:

if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression

Throws:

XPathException - if any error is detected

iterateSubExpressions

public java.util.Iterator iterateSubExpressions()

Get the immediate subexpressions of this expression

Specified by:

iterateSubExpressions in interface Expression

Overrides:

iterateSubExpressions in class ComputedExpression

Returns:

an iterator containing the sub-expressions of this expression

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)

Replace one subexpression by a replacement subexpression

Specified by:

replaceSubExpression in interface Container

Overrides:

replaceSubExpression in class ComputedExpression

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

suppressValidation

public void suppressValidation(int validationMode)

Suppress validation on contained element constructors, on the grounds that the parent element is already performing validation. The default implementation does nothing.

Overrides:

suppressValidation in class ComputedExpression

markTailFunctionCalls

public boolean markTailFunctionCalls(int nameCode,
                                     int arity)

Mark tail calls on used-defined functions. For most expressions, this does nothing.

Overrides:

markTailFunctionCalls in class ComputedExpression

Returns:

true if a tail recursive call was found and if this call accounts for the whole of the value.

checkPermittedContents

public void checkPermittedContents(SchemaType parentType,
                                   StaticContext env,
                                   boolean whole)
                            throws XPathException

Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type. It's always OK to say yes, since the check will be repeated at run-time. The process of checking element and attribute constructors against the content model of a complex type also registers the type of content expected of those constructors, so the static validation can continue recursively.

Specified by:

checkPermittedContents in interface Expression

Overrides:

checkPermittedContents in class ComputedExpression

Parameters:

parentType - The schema type

env - the static context

whole - true if this expression is expected to make the whole content of the type, false if it is expected to make up only a part

Throws:

XPathException - if the expression doesn't match the required content type

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate the conditional expression in a given context

Specified by:

evaluateItem in interface Expression

Overrides:

evaluateItem in class ComputedExpression

Parameters:

context - the evaluation context

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

Iterate the path-expression in a given context

Specified by:

iterate in interface Expression

Overrides:

iterate in class ComputedExpression

Parameters:

context - the evaluation context

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 this expression as an instruction, writing results to the current receiver

Specified by:

process in interface Expression

Overrides:

process in class ComputedExpression

Parameters:

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

Throws:

XPathException

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
                            throws XPathException

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

getItemType

public ItemType getItemType(TypeHierarchy th)

Get data type of items in sequence returned by expression

Specified by:

getItemType in interface Expression

Parameters:

th -

Returns:

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

computeCardinality

public int computeCardinality()

Determine the static cardinality of the result

Specified by:

computeCardinality in class ComputedExpression

computeSpecialProperties

public int computeSpecialProperties()

Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

Overrides:

computeSpecialProperties in class ComputedExpression

display

public void display(int level,
                    java.io.PrintStream out,
                    Configuration config)

Diagnostic print of expression structure

Specified by:

display in interface Expression

Parameters:

level - indentation level for this expression

out - Output destination