net.sf.saxon.sort
Class TupleExpression

java.lang.Object
  net.sf.saxon.expr.Expression
      net.sf.saxon.sort.TupleExpression

All Implemented Interfaces:

Serializable, SourceLocator, EvaluableItem, SequenceIterable, InstructionInfoProvider

public class TupleExpression
extends Expression

A tuple expression is an expression that returns a tuple. Specifically, it is a list of n expressions, which are evaluated to create a list of n items. Tuple expressions are used during the evaluation of a FLWR expression. A tuple is not a value within the XPath/XQuery type system, so it is represented as an external object, specifically as a Java array wrapped inside an ObjectValue.

See Also:

Serialized Form

Field Summary

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

TupleExpression(int width)

Method Summary

int	computeCardinality() Get the cardinality 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.
Expression[]	getComponents() Get the component expressions
int	getIntrinsicDependencies() Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions.
ItemType	getItemType(TypeHierarchy th) Determine the data type of the expression, if possible.
Iterator	iterateSubExpressions() Get the immediate sub-expressions of this expression.
Expression	optimize(ExpressionVisitor visitor, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	promote(PromotionOffer offer) Offer promotion for this subexpression.
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
void	setExpression(int i, Expression exp) Set the i'th component expression of the tuple
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, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, effectiveBooleanValue, evaluateAsString, explain, findParentOf, getCardinality, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterate, iterateEvents, markTailFunctionCalls, process, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toString

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

TupleExpression

public TupleExpression(int width)

Method Detail

setExpression

public void setExpression(int i,
                          Expression exp)

Set the i'th component expression of the tuple

Parameters:

i - identifies the component to set

exp - the component expression

getComponents

public Expression[] getComponents()

Get the component expressions

Returns:

the component expressions, as an array

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException

Description copied from class: Expression

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

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException

Description copied from class: Expression

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

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

getItemType

public ItemType getItemType(TypeHierarchy th)

Description copied from class: Expression

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)

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 parent pointer and 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

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 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)

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

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

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Description copied from class: Expression

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

computeCardinality

public int computeCardinality()

Get the cardinality of the expression. This is exactly one, in the sense that evaluating the TupleExpression returns a single tuple.

Returns:

the static cardinality - EXACTLY_ONE

getIntrinsicDependencies

public int getIntrinsicDependencies()

Description copied from class: Expression

Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions. For example, position() has an intrinsic dependency on the context position, while (position()+1) does not. The default implementation of the method returns 0, indicating "no dependencies".

Overrides:

getIntrinsicDependencies in class Expression

Returns:

a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty

iterateSubExpressions

public Iterator iterateSubExpressions()

Description copied from class: Expression

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