net.sf.saxon.instruct

Class SimpleContentConstructor

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.
Field Summary
booleanisAtomic
booleanisSingleton
Expressionselect
Expressionseparator
Constructor Summary
SimpleContentConstructor(Expression select, Expression separator)
Create a SimpleContentConstructor
Method Summary
protected intcomputeCardinality()
Compute the cardinality of the result of the expression.
Expressioncopy()
Copy an expression.
ItemevaluateItem(XPathContext context)
Evaluate an expression as a single item.
voidexplain(ExpressionPresenter out)
Diagnostic print of expression structure.
intgetImplementationMethod()
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
ItemTypegetItemType(TypeHierarchy th)
Determine the data type of the expression, if possible.
ExpressiongetSelectExpression()
Get the select expression
ExpressiongetSeparatorExpression()
Get the separator expression
booleanisAtomic()
Determine if the select expression is atomic
booleanisSingleton()
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.
Expressionoptimize(ExpressionVisitor visitor, ItemType contextItemType)
voidprocess(XPathContext context, int locationId, int options)
Process the instruction, without returning any tail calls
voidprocessLeft(Stack<XPathContext> contextStack, Stack state)
In streaming mode, process the first half of the instruction (for example, to start a new document or element)
voidprocessRight(Stack<XPathContext> contextStack, Stack state)
In streaming mode, process the right half of the instruction (for example, to end a new document or element)
Expressionpromote(PromotionOffer offer, Expression parent)
Offer promotion for this subexpression.
booleanreplaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression
Expressionsimplify(ExpressionVisitor visitor)
Simplify an expression.
ExpressiontypeCheck(ExpressionVisitor visitor, ItemType contextItemType)

Field Detail

isAtomic

boolean isAtomic

isSingleton

boolean isSingleton

select

Expression select

separator

Expression separator

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

computeCardinality

protected int computeCardinality()
Compute the cardinality of the result of the expression.

Returns: the cardinality, @link {StaticProperty.EXACTLY_ONE}

copy

public Expression copy()
Copy an expression. This makes a deep copy.

Returns: the copy of the original expression

evaluateItem

public Item evaluateItem(XPathContext context)
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.

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: net.sf.saxon.trans.XPathException if any dynamic error occurs evaluating the expression

explain

public void explain(ExpressionPresenter out)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

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.

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.

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)

getSelectExpression

public Expression getSelectExpression()
Get the select expression

Returns: the select expression

getSeparatorExpression

public Expression getSeparatorExpression()
Get the separator expression

Returns: the separator expression

isAtomic

public boolean isAtomic()
Determine if the select expression is atomic

Returns: true if the select expression always returns atomic values

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

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.

Returns: an iterator containing the sub-expressions of this expression

optimize

public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)

process

public void process(XPathContext context, int locationId, int options)
Process the instruction, without returning any tail calls

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

processLeft

public 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)

Parameters: contextStack state a stack on which the instruction can save state information during the call on processLeft()

processRight

public 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)

Parameters: contextStack state a stack on which the instruction can save state information during the call on processLeft()

promote

public Expression promote(PromotionOffer offer, Expression parent)
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.

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: net.sf.saxon.trans.XPathException if any error is detected

replaceSubExpression

public boolean replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression

Parameters: original the original subexpression replacement the replacement subexpression

Returns: true if the original subexpression is found

simplify

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

Parameters: visitor an expression visitor

Returns: the simplified expression

Throws: net.sf.saxon.trans.XPathException if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)