pub type lv_iter_next_cb = Option<unsafe extern "C" fn(*mut c_void, *mut c_void, *mut c_void) -> u32>;
pub enum lv_iter_next_cb { None, Some(unsafe extern "C" fn(*mut c_void, *mut c_void, *mut c_void) -> u32), }
No value.
Some value of type T.
T