pub type log_handler_t = Option<unsafe extern "C" fn(lvl: c_int, msg: *const c_char, args: va_list, p: *mut c_void)>;
enum log_handler_t { None, Some(unsafe extern "C" fn(_: i32, _: *const i8, _: *mut i8, _: *mut c_void)), }
No value.
Some value of type T.
T