pub type R_altinteger_Elt_method_t = Option<unsafe extern "C" fn(arg1: SEXP, arg2: R_xlen_t) -> c_int>;
pub enum R_altinteger_Elt_method_t { None, Some(unsafe extern "C" fn(*mut SEXPREC, isize) -> i32), }
No value.
Some value of type T.
T