pub type PFNGLCOLOR4XPROC = Option<unsafe extern "C" fn(red: GLfixed, green: GLfixed, blue: GLfixed, alpha: GLfixed)>;
enum PFNGLCOLOR4XPROC { None, Some(unsafe extern "C" fn(_: i32, _: i32, _: i32, _: i32)), }
No value.
Some value of type T.
T