functionAddress = @fn FunctionName
Returns a memory address which can be used to access the function specified by FunctionName.
FunctionName must be the name of a function which was defined or prototyped at some earlier location in the source code, in a local fn, def fn
<expr>, or def fn
The address returned by @fn can be used in a def fn using statement, or as a parameter to a Toolbox function that expects the address of a callback function.
def fn using