net.sf.saxon.functions
Class ItemAt

java.lang.Object
  net.sf.saxon.lib.ExtensionFunctionDefinition
      net.sf.saxon.functions.ItemAt

All Implemented Interfaces:

Serializable

public class ItemAt
extends ExtensionFunctionDefinition

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.

See Also:

Serialized Form

Constructor Summary

ItemAt()

Method Summary

SequenceType[]	getArgumentTypes() Get the required types for the arguments of this function, counting from zero
StructuredQName	getFunctionQName() Get the function name, as a QName
int	getMaximumNumberOfArguments() Get the maximum number of arguments allowed by the function
int	getMinimumNumberOfArguments() Get the minimum number of arguments required by the function
SequenceType	getResultType(SequenceType[] suppliedArgumentTypes) Get the type of the result of the function
ExtensionFunctionCall	makeCallExpression() Create a call on this function.
boolean	trustResultType() Ask whether the result actually returned by the function can be trusted, or whether it should be checked against the declared type.

Methods inherited from class net.sf.saxon.lib.ExtensionFunctionDefinition

dependsOnFocus, hasSideEffects

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ItemAt

public ItemAt()

Method Detail

getFunctionQName

public StructuredQName getFunctionQName()

Get the function name, as a QName

Specified by:

getFunctionQName in class ExtensionFunctionDefinition

Returns:

the QName of the function

getMinimumNumberOfArguments

public int getMinimumNumberOfArguments()

Get the minimum number of arguments required by the function

Overrides:

getMinimumNumberOfArguments in class ExtensionFunctionDefinition

Returns:

the minimum number of arguments that must be supplied in a call to this function

getMaximumNumberOfArguments

public int getMaximumNumberOfArguments()

Get the maximum number of arguments allowed by the function

Overrides:

getMaximumNumberOfArguments in class ExtensionFunctionDefinition

Returns:

the maximum number of arguments that may be supplied in a call to this function

getArgumentTypes

public SequenceType[] getArgumentTypes()

Get the required types for the arguments of this function, counting from zero

Specified by:

getArgumentTypes in class ExtensionFunctionDefinition

Returns:

the required types of the argument, as defined by the function signature. Normally this should be an array of size getMaximumNumberOfArguments(); however for functions that allow a variable number of arguments, the array can be smaller than this, with the last entry in the array providing the required type for all the remaining arguments.

getResultType

public SequenceType getResultType(SequenceType[] suppliedArgumentTypes)

Get the type of the result of the function

Specified by:

getResultType in class ExtensionFunctionDefinition

Parameters:

suppliedArgumentTypes - the static types of the arguments to the function. This is provided so that a more precise result type can be returned in the common case where the type of the result depends on the type of the first argument. The value will be null if the function call has no arguments.

Returns:

the return type of the function, as defined by its function signature

trustResultType

public boolean trustResultType()

Ask whether the result actually returned by the function can be trusted, or whether it should be checked against the declared type.

Overrides:

trustResultType in class ExtensionFunctionDefinition

Returns:

true if the function implementation warrants that the value it returns will be an instance of the declared result type. The default value is false, in which case the result will be checked at run-time to ensure that it conforms to the declared type. If the value true is returned, but the function returns a value of the wrong type, the consequences are unpredictable.

makeCallExpression

public ExtensionFunctionCall makeCallExpression()

Create a call on this function. This method is called by the compiler when it identifies a function call that calls this function.

Specified by:

makeCallExpression in class ExtensionFunctionDefinition

Returns:

an expression representing a call of this extension function