net.sf.saxon.sort
Class TupleExpression

java.lang.Object
  extended bynet.sf.saxon.expr.ComputedExpression
      extended bynet.sf.saxon.sort.TupleExpression
All Implemented Interfaces:
Expression, Serializable

public class TupleExpression
extends ComputedExpression

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
(package private)  Expression[] components
           
 
Fields inherited from class net.sf.saxon.expr.ComputedExpression
lineNumber, NO_ARGUMENTS, staticProperties
 
Constructor Summary
TupleExpression(int width)
           
 
Method Summary
 Expression analyze(StaticContext env)
          Perform static analysis of an expression and its subexpressions.
 int computeCardinality()
          Get the cardinality of the expression.
 void display(int level, NamePool pool)
          Diagnostic print of expression structure.
 Item evaluateItem(XPathContext context)
          Evaluate an expression as a single item.
 int getIntrinsicDependencies()
          Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions.
 ItemType getItemType()
          Determine the data type of the expression, if possible.
 Expression[] getSubExpressions()
          Get the immediate sub-expressions of this expression.
 SequenceIterator iterate(XPathContext context)
          Return an Iterator to iterate over the values of a sequence.
 Expression promote(PromotionOffer offer)
          Offer promotion for this subexpression.
 void setExpression(int i, Expression exp)
           
 Expression simplify()
          Simplify an expression.
 
Methods inherited from class net.sf.saxon.expr.ComputedExpression
computeDependencies, computeSpecialProperties, computeStaticProperties, dynamicError, effectiveBooleanValue, evaluateAsString, getCardinality, getDependencies, getLineNumber, getSpecialProperties, markTailFunctionCalls, setLineNumber, typeError
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

components

Expression[] components
Constructor Detail

TupleExpression

public TupleExpression(int width)
Method Detail

setExpression

public void setExpression(int i,
                          Expression exp)

simplify

public Expression simplify()
                    throws XPathException
Description copied from class: ComputedExpression
Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.

Specified by:
simplify in interface Expression
Overrides:
simplify in class ComputedExpression
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: ComputedExpression
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.

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

getItemType

public ItemType getItemType()
Description copied from interface: 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.

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

analyze

public Expression analyze(StaticContext env)
                   throws XPathException
Description copied from interface: Expression
Perform static analysis of an expression and its subexpressions.

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 will only be accurately known if they have been explicitly declared.

Parameters:
env - the static context of the expression
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)

display

public void display(int level,
                    NamePool pool)
Description copied from interface: Expression
Diagnostic print of expression structure. The expression is written to the System.err output stream

Parameters:
level - indentation level for this expression

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException
Description copied from class: ComputedExpression
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 Expression
Overrides:
evaluateItem in class ComputedExpression
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.

Specified by:
computeCardinality in class ComputedExpression
Returns:
the static cardinality - EXACTLY_ONE

getIntrinsicDependencies

public int getIntrinsicDependencies()
Description copied from class: ComputedExpression
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 ComputedExpression
Returns:
a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty

getSubExpressions

public Expression[] getSubExpressions()
Description copied from class: ComputedExpression
Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

Specified by:
getSubExpressions in interface Expression
Overrides:
getSubExpressions in class ComputedExpression
Returns:
an array containing the sub-expressions of this expression

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException
Description copied from class: ComputedExpression
Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.

Specified by:
iterate in interface Expression
Overrides:
iterate in class ComputedExpression
Parameters:
context - supplies the context for evaluation
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