pub type PFNGLWINDOWPOS3SARBPROC = Option<unsafe extern "C" fn(x: GLshort, y: GLshort, z: GLshort)>;
enum PFNGLWINDOWPOS3SARBPROC { None, Some(unsafe extern "C" fn(_: i16, _: i16, _: i16)), }
No value.
Some value of type T.
T