pub type lv_circle_buf_fill_cb_t = Option<unsafe extern "C" fn(*mut c_void, u32, i32, *mut c_void) -> bool>;
pub enum lv_circle_buf_fill_cb_t { None, Some(unsafe extern "C" fn(*mut c_void, u32, i32, *mut c_void) -> bool), }
No value.
Some value of type T.
T