pub type PFNGLMULTITEXCOORD2DARBPROC = Option<unsafe extern "C" fn(target: GLenum, s: GLdouble, t: GLdouble)>;
enum PFNGLMULTITEXCOORD2DARBPROC { None, Some(unsafe extern "C" fn(_: u32, _: f64, _: f64)), }
No value.
Some value of type T.
T