pub type cairo_read_func_t = Option<unsafe extern "C" fn(_: *mut c_void, _: *mut c_uchar, _: c_uint) -> cairo_status_t>;
enum cairo_read_func_t { None, Some(unsafe extern "C" fn(_: *mut c_void, _: *mut u8, _: u32) -> i32), }
No value.
Some value of type T.
T