pub type lv_display_flush_cb_t = Option<unsafe extern "C" fn(*mut _lv_display_t, *const lv_area_t, *mut u8)>;
pub enum lv_display_flush_cb_t { None, Some(unsafe extern "C" fn(*mut _lv_display_t, *const lv_area_t, *mut u8)), }
No value.
Some value of type T.
T