net.sf.saxon.sort
Class TupleSorter

java.lang.Object
  extended bynet.sf.saxon.expr.ComputedExpression
      extended bynet.sf.saxon.sort.TupleSorter
All Implemented Interfaces:
Container, Expression, InstructionInfoProvider, MappingFunction, java.io.Serializable, javax.xml.transform.SourceLocator

public class TupleSorter
extends ComputedExpression
implements MappingFunction

A TupleSorter is an expression that sorts a stream of tuples. It is used to implement XQuery FLWR expressions.

See Also:
Serialized Form

Field Summary
 
Fields inherited from class net.sf.saxon.expr.ComputedExpression
locationId, staticProperties
 
Fields inherited from interface net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
 
Constructor Summary
TupleSorter(Expression base, FixedSortKeyDefinition[] keys)
           
 
Method Summary
 Expression analyze(StaticContext env, ItemType contextItemType)
          Perform static analysis and optimisation of an expression and its subexpressions.
 int computeCardinality()
           
 void display(int level, NamePool pool, java.io.PrintStream out)
          Diagnostic print of expression structure.
 boolean effectiveBooleanValue(XPathContext context)
          Get the effective boolean value of the expression.
 ItemType getItemType()
          Determine the data type of the expression, if possible.
 boolean isSortKey(Expression child)
          Test whether a given expression is one of the sort keys
 SequenceIterator iterate(XPathContext context)
          Return an Iterator to iterate over the values of a sequence.
 java.util.Iterator iterateSubExpressions()
          Get the immediate sub-expressions of this expression.
 java.lang.Object map(Item item, XPathContext context, java.lang.Object info)
          Mapping function to map the wrapped objects returned by the SortedTupleIterator into real items.
 Expression promote(PromotionOffer offer)
          Promote this expression if possible
 Expression simplify(StaticContext env)
          Simplify an expression.
 
Methods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, checkPermittedContents, computeDependencies, computeSpecialProperties, computeStaticProperties, dynamicError, dynamicError, evaluateAsString, evaluateItem, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getParentExpression, getPublicId, getSpecialProperties, getSystemId, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, typeError, typeError
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

TupleSorter

public TupleSorter(Expression base,
                   FixedSortKeyDefinition[] keys)
Method Detail

simplify

public Expression simplify(StaticContext env)
                    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

analyze

public Expression analyze(StaticContext env,
                          ItemType contextItemType)
                   throws XPathException
Description copied from interface: Expression
Perform static analysis and optimisation 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 may not be accurately known if they have not been explicitly declared.

Specified by:
analyze in interface Expression
Parameters:
env - the static context of the expression
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

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.

Specified by:
getItemType in interface Expression
Returns:
a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)

computeCardinality

public int computeCardinality()
Specified by:
computeCardinality in class ComputedExpression

iterateSubExpressions

public java.util.Iterator iterateSubExpressions()
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:
iterateSubExpressions in interface Expression
Overrides:
iterateSubExpressions in class ComputedExpression
Returns:
an iterator containing the sub-expressions of this expression

isSortKey

public boolean isSortKey(Expression child)
Test whether a given expression is one of the sort keys


promote

public Expression promote(PromotionOffer offer)
                   throws XPathException
Promote this expression if possible

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

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

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
                              throws XPathException
Description copied from class: ComputedExpression
Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.

Specified by:
effectiveBooleanValue in interface Expression
Overrides:
effectiveBooleanValue in class ComputedExpression
Parameters:
context - The context in which the expression is to be evaluated
Returns:
the effective boolean value
Throws:
XPathException - if any dynamic error occurs evaluating the expression

display

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

Specified by:
display in interface Expression
Parameters:
level - indentation level for this expression
pool - NamePool used to expand any names appearing in the expression
out - Output destination

map

public java.lang.Object map(Item item,
                            XPathContext context,
                            java.lang.Object info)
                     throws XPathException
Mapping function to map the wrapped objects returned by the SortedTupleIterator into real items. This is done because each tuple may actually represent a sequence of underlying values that share the same sort key.

Specified by:
map in interface MappingFunction
Parameters:
item - The item to be mapped. If context is supplied, this must be the same as context.currentItem().
context - The processing context. This is supplied only for mapping constructs that set the context node, position, and size. Otherwise it is null.
info - Arbitrary information supplied by the creator of the MappingIterator. It must be read-only and immutable for the duration of the iteration.
Returns:
either (a) a SequenceIterator over the sequence of items that the supplied input item maps to, or (b) an Item if it maps to a single item, or (c) null if it maps to an empty sequence.
Throws:
XPathException