net.sf.saxon.instruct
Class SimpleContentConstructor

java.lang.Object
  net.sf.saxon.expr.Expression
      net.sf.saxon.instruct.SimpleContentConstructor

All Implemented Interfaces:

Serializable, SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, DivisibleInstruction, InstructionInfo, Locator

Direct Known Subclasses:

QuerySimpleContentConstructor

public class SimpleContentConstructor
extends Expression
implements DivisibleInstruction

This class implements the rules for an XSLT (or XQuery) simple content constructor, which are used in constructing the string value of an attribute node, text node, comment node, etc, from the value of the select expression or the contained sequence constructor.

See Also:

Serialized Form

Field Summary

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

EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties

Constructor Summary

SimpleContentConstructor(Expression select, Expression separator)
Create a SimpleContentConstructor

Method Summary

protected int	computeCardinality() Compute the cardinality of the result of the expression.
Expression	copy() Copy an expression.
Item	evaluateItem(XPathContext context) Evaluate an expression as a single item.
void	explain(ExpressionPresenter out) 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(TypeHierarchy th) Determine the data type of the expression, if possible.
Expression	getSelectExpression() Get the select expression
Expression	getSeparatorExpression() Get the separator expression
boolean	isAtomic() Determine if the select expression is atomic
boolean	isSingleton() Determine whether the select expression is a singleton (an expression returning zero or one items)
Iterator<Expression>	iterateSubExpressions() Get the immediate sub-expressions of this expression.
Expression	optimize(ExpressionVisitor visitor, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
void	process(XPathContext context, int locationId, int options) Process the instruction, without returning any tail calls
void	processLeft(Stack<XPathContext> contextStack, Stack state) In streaming mode, process the first half of the instruction (for example, to start a new document or element)
void	processRight(Stack<XPathContext> contextStack, Stack state) In streaming mode, process the right half of the instruction (for example, to end a new document or element)
Expression	promote(PromotionOffer offer, Expression parent) Offer promotion for this subexpression.
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
Expression	simplify(ExpressionVisitor visitor) Simplify an expression.
Expression	typeCheck(ExpressionVisitor visitor, ItemType contextItemType) Perform type checking of an expression and its subexpressions.

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

addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeSpecialProperties, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toString, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

SimpleContentConstructor

public SimpleContentConstructor(Expression select,
                                Expression separator)

Create a SimpleContentConstructor

Parameters:

select - the select expression (which computes a sequence of strings)

separator - the separator expression (which computes a value to separate adjacent strings)

Method Detail

getSelectExpression

public Expression getSelectExpression()

Get the select expression

Returns:

the select expression

getSeparatorExpression

public Expression getSeparatorExpression()

Get the separator expression

Returns:

the separator expression

isSingleton

public boolean isSingleton()

Determine whether the select expression is a singleton (an expression returning zero or one items)

Returns:

true if the select expression will always be of length zero or one

isAtomic

public boolean isAtomic()

Determine if the select expression is atomic

Returns:

true if the select expression always returns atomic values

computeCardinality

protected int computeCardinality()

Compute the cardinality of the result of the expression.

Specified by:

computeCardinality in class Expression

Returns:

the cardinality, @link {StaticProperty.EXACTLY_ONE}

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

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException

Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.

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,
                            ItemType contextItemType)
                     throws XPathException

Description copied from class: Expression

Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.

If the implementation returns a value other than "this", then it is required to ensure that the location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.

Overrides:

typeCheck in class Expression

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 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,
                           ItemType contextItemType)
                    throws XPathException

Description copied from class: 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.

Overrides:

optimize in class Expression

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)

getItemType

public ItemType getItemType(TypeHierarchy th)

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

Parameters:

th - the type hierarchy cache

Returns:

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

explain

public void explain(ExpressionPresenter out)

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

Specified by:

explain in class Expression

Parameters:

out - the expression presenter used to display the structure

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()

Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

Overrides:

iterateSubExpressions in class Expression

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

Overrides:

replaceSubExpression in class Expression

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

promote

public Expression promote(PromotionOffer offer,
                          Expression parent)
                   throws XPathException

Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is not accepted - this is appropriate in the case of simple expressions such as constant values and variable references where promotion would give no performance advantage. This method is always called at compile time.

Overrides:

promote in class Expression

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

parent -

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

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.

Specified by:

evaluateItem in interface EvaluableItem

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,
                    int locationId,
                    int options)
             throws XPathException

Process the instruction, without returning any tail calls

Parameters:

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

Throws:

XPathException

processLeft

public void processLeft(Stack<XPathContext> contextStack,
                        Stack state)
                 throws XPathException

In streaming mode, process the first half of the instruction (for example, to start a new document or element)

Specified by:

processLeft in interface DivisibleInstruction

Parameters:

contextStack -

state - a stack on which the instruction can save state information during the call on processLeft()

Throws:

XPathException

processRight

public void processRight(Stack<XPathContext> contextStack,
                         Stack state)
                  throws XPathException

In streaming mode, process the right half of the instruction (for example, to end a new document or element)

Specified by:

processRight in interface DivisibleInstruction

Parameters:

contextStack -

state - a stack on which the instruction can save state information during the call on processLeft()

Throws:

XPathException

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 prefered.

Overrides:

getImplementationMethod in class Expression

Returns:

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