pub type uv_read_cb = Option<unsafe extern "C" fn(stream: *mut uv_stream_t, nread: isize, buf: *const uv_buf_t)>;
enum uv_read_cb { None, Some(unsafe extern "C" fn(_: *mut uv_stream_s, _: isize, _: *const uv_buf_t)), }
No value.
Some value of type T.
T