pub type PFNGLUNIFORM3DPROC = Option<unsafe extern "C" fn(_: i32, _: f64, _: f64, _: f64)>;
enum PFNGLUNIFORM3DPROC { None, Some(unsafe extern "C" fn(_: i32, _: f64, _: f64, _: f64)), }
No value.
Some value of type T.
T