pub type FPtr_gctx_tickmarks = Option<unsafe extern "C" fn(item: *mut c_void, num_tickmarks: u32, tickmarks_at_left_top: bool_t)>;
pub enum FPtr_gctx_tickmarks { None, Some(unsafe extern "C" fn(*mut c_void, u32, i8)), }
No value.
Some value of type T.
T