net.sf.saxon.functions
Class ItemAt
- EvaluableItem, InstructionInfoProvider, SequenceIterable, Serializable, SourceLocator
Implements the saxon:item-at() function. This is handled specially because it is generated
by the optimizer.
The function takes two arguments: the first is an arbitrary sequence, the second is optional numeric.
The function returns the same result as let $N := NUMBER return SEQUENCE[$N], including cases where the
numeric argument is not a whole number.
addContextDocumentArgument , addDocToPathMap , checkArguments , computeCardinality , computeSpecialProperties , copy , getDetails , getErrorCodeForTypeErrors , getItemType , getRequiredType , makeSystemFunction , optimize , setDetails , useContextItemAsDefault |
addExternalFunctionCallToPathMap , checkArgumentCount , checkArguments , equals , explain , getArguments , getDisplayName , getFunctionName , getNumberOfArguments , hashCode , iterateSubExpressions , optimize , preEvaluate , promote , replaceSubExpression , setArguments , setFunctionName , simplify , simplifyArguments , toString , typeCheck |
addToPathMap , adoptChildExpression , checkPermittedContents , computeCardinality , computeDependencies , computeSpecialProperties , computeStaticProperties , copy , display , doPromotion , dynamicError , effectiveBooleanValue , evaluateAsString , evaluateItem , explain , explain , findParentOf , getCardinality , getColumnNumber , getConstructType , getContainer , getDependencies , getExecutable , getHostLanguage , getImplementationMethod , getInstructionInfo , getIntrinsicDependencies , getItemType , getLineNumber , getLocationId , getLocationProvider , getPublicId , getSlotsUsed , getSpecialProperties , getSystemId , hasLoopingSubexpression , implementsStaticTypeCheck , iterate , iterateEvents , iterateSubExpressions , markTailFunctionCalls , optimize , process , promote , replaceSubExpression , resetLocalStaticProperties , setContainer , setFiltered , setFlattened , setLocationId , simplify , staticTypeCheck , suppressValidation , toString , typeCheck , typeError |
optimize
public Expression optimize(ExpressionVisitor visitor,
ItemType contextItemType)
throws XPathException
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.
- optimize in interface SystemFunction
visitor
- an expression visitorcontextItemType
- 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
- the original expression, rewritten if appropriate to optimize execution
XPathException
- if an error is discovered during this phase
(typically a type error)