pub type sd_progress_cb_t = Option<unsafe extern "C" fn(step: c_int, steps: c_int, time: f32, data: *mut c_void)>;
enum sd_progress_cb_t { None, Some(unsafe extern "C" fn(_: i32, _: i32, _: f32, _: *mut c_void)), }
No value.
Some value of type T.
T