net.sf.saxon.functions
public class Existence extends SystemFunction implements Negatable
Field Summary | |
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static int | EMPTY |
static int | EXISTS |
Method Summary | |
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void | checkArguments(ExpressionVisitor visitor)
Static analysis: prevent sorting of the argument |
boolean | effectiveBooleanValue(XPathContext c)
Evaluate the function in a boolean context |
Item | evaluateItem(XPathContext c)
Evaluate in a general context |
boolean | isNegatable(ExpressionVisitor visitor)
Check whether this specific instance of the expression is negatable
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Expression | negate()
Return the negation of the expression |
Expression | optimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
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Returns: true if it is
Returns: the negation 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, and after all type checking has been done.
Parameters: visitor an expression visitor 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.XPathException if an error is discovered during this phase (typically a type error)