pub type PFNGLCOLOR4HNVPROC = Option<unsafe extern "C" fn(red: GLhalf, green: GLhalf, blue: GLhalf, alpha: GLhalf)>;
enum PFNGLCOLOR4HNVPROC { None, Some(unsafe extern "C" fn(_: u16, _: u16, _: u16, _: u16)), }
No value.
Some value of type T.
T