net.sf.saxon.expr
public final class FirstItemExpression extends UnaryExpression
Constructor Summary | |
---|---|
FirstItemExpression(Expression base)
Constructor |
Method Summary | |
---|---|
int | computeCardinality()
Get the static cardinality |
String | displayOperator(NamePool pool)
Diagnostic print of expression structure |
Item | evaluateItem(XPathContext context)
Evaluate the expression |
Expression | optimize(Optimizer opt, StaticContext env, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
|
Expression | promote(PromotionOffer offer)
Promote this expression if possible |
Parameters: base A sequence expression denoting sequence whose first item is to be returned
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)