net.sf.saxon.sort
Class TupleExpression
- EvaluableItem, InstructionInfoProvider, SequenceIterable, Serializable, SourceLocator
public class TupleExpression
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.
addToPathMap , adoptChildExpression , checkPermittedContents , computeCardinality , computeDependencies , computeSpecialProperties , computeStaticProperties , copy , display , doPromotion , dynamicError , effectiveBooleanValue , evaluateAsString , evaluateItem , explain , explain , findParentOf , getCardinality , getColumnNumber , getConstructType , getContainer , getDependencies , getExecutable , getHostLanguage , getImplementationMethod , getInstructionInfo , getIntrinsicDependencies , getItemType , getLineNumber , getLocationId , getLocationProvider , getPublicId , getSlotsUsed , getSpecialProperties , getSystemId , hasLoopingSubexpression , implementsStaticTypeCheck , iterate , iterateEvents , iterateSubExpressions , markTailFunctionCalls , optimize , process , promote , replaceSubExpression , resetLocalStaticProperties , setContainer , setFiltered , setFlattened , setLocationId , simplify , staticTypeCheck , suppressValidation , toString , typeCheck , typeError |
TupleExpression
public TupleExpression(int width)
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.
- computeCardinality in interface Expression
- the static cardinality - EXACTLY_ONE
copy
public Expression copy()
Copy an expression. This makes a deep copy.
- copy in interface Expression
- the copy of the original expression
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.
- evaluateItem in interface EvaluableItem
- evaluateItem in interface Expression
context
- The context in which the expression is to be evaluated
- the node or atomic value that results from evaluating the
expression; or null to indicate that the result is an empty
sequence
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.
- explain in interface Expression
getComponents
public Expression[] getComponents()
Get the component expressions
- the component expressions, as an array
getIntrinsicDependencies
public int getIntrinsicDependencies()
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".
- getIntrinsicDependencies in interface Expression
- a set of bit-significant flags identifying the "intrinsic"
dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty
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.
- getItemType in interface Expression
th
- the type hierarchy cache
- a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER,
Type.NODE, or Type.ITEM (meaning not known at compile time)
iterateSubExpressions
public Iterator 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.
- iterateSubExpressions in interface Expression
- an iterator containing the sub-expressions of this expression
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.
- optimize in interface Expression
visitor
- an expression visitorcontextItemType
- 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
- the original expression, rewritten if appropriate to optimize execution
XPathException
- if an error is discovered during this phase
(typically a type error)
promote
public Expression promote(PromotionOffer offer)
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.
- promote in interface Expression
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
- if the offer is not accepted, return this expression unchanged.
Otherwise return the result of rewriting the expression to promote
this subexpression
replaceSubExpression
public boolean replaceSubExpression(Expression original,
Expression replacement)
Replace one subexpression by a replacement subexpression
- replaceSubExpression in interface Expression
original
- the original subexpressionreplacement
- the replacement subexpression
- true if the original subexpression is found
setExpression
public void setExpression(int i,
Expression exp)
Set the i'th component expression of the tuple
i
- identifies the component to setexp
- the component 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.
- simplify in interface Expression
visitor
- an expression visitor
- the simplified expression
XPathException
- if an error is discovered during expression
rewriting
typeCheck
public Expression typeCheck(ExpressionVisitor visitor,
ItemType contextItemType)
throws XPathException
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.
- typeCheck in interface Expression
visitor
- an expression visitorcontextItemType
- 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
- the original expression, rewritten to perform necessary run-time type checks,
and to perform other type-related optimizations
XPathException
- if an error is discovered during this phase
(typically a type error)