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