net.sf.saxon.sort

Class SortExpression

public class SortExpression extends ComputedExpression

Expression equivalent to the imaginary syntax expr sortby (sort-key)+
Constructor Summary
SortExpression(Expression select, SortKeyDefinition[] sortKeys)
Method Summary
intcomputeCardinality()
Determine the static cardinality
intcomputeSpecialProperties()
Get the static properties of this expression (other than its type).
voiddisplay(int level, NamePool pool, PrintStream out)
ItemTypegetItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possible
booleanisSortKey(Expression child)
Test whether a given expression is one of the sort keys
SequenceIteratoriterate(XPathContext context)
Enumerate the results of the expression
IteratoriterateSubExpressions()
Get the immediate sub-expressions of this expression.
Expressionoptimize(Optimizer opt, StaticContext env, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
Expressionpromote(PromotionOffer offer)
Offer promotion for this subexpression.
Expressionsimplify(StaticContext env)
Simplify an expression
ExpressiontypeCheck(StaticContext env, ItemType contextItemType)
Type-check the expression

Constructor Detail

SortExpression

public SortExpression(Expression select, SortKeyDefinition[] sortKeys)

Method Detail

computeCardinality

public int computeCardinality()
Determine the static cardinality

computeSpecialProperties

public int computeSpecialProperties()
Get the static properties of this expression (other than its type). The result is bit-significant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

display

public void display(int level, NamePool pool, PrintStream out)

getItemType

public ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possible

Parameters: th

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

isSortKey

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

iterate

public SequenceIterator iterate(XPathContext context)
Enumerate the results of the expression

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.

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

optimize

public Expression optimize(Optimizer opt, StaticContext env, ItemType contextItemType)
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.

Parameters: opt the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances. 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 ITEM_TYPE

Returns: the original expression, rewritten if appropriate to optimize execution

Throws: net.sf.saxon.trans.StaticError if an error is discovered during this phase (typically a type error)

promote

public Expression promote(PromotionOffer offer)
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

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

simplify

public Expression simplify(StaticContext env)
Simplify an expression

typeCheck

public Expression typeCheck(StaticContext env, ItemType contextItemType)
Type-check the expression