pub type k_thread_entry_t = Option<unsafe extern "C" fn(_: *mut c_void, _: *mut c_void, _: *mut c_void)>;
enum k_thread_entry_t { None, Some(unsafe extern "C" fn(_: *mut c_void, _: *mut c_void, _: *mut c_void)), }
No value.
Some value of type T.
T