Determines whether f acts as a standard S3-style generic
function.
isS3stdGeneric(f)A function object
If f is an S3 generic, a logical vector containing TRUE
with the name of the S3 generic (the string passed to
UseMethod). Otherwise, FALSE (unnamed).
A closure is considered a standard S3 generic if the first expression
in its body calls UseMethod. Functions which perform
operations before calling UseMethod will not be considered
“standard” S3 generics.