pub type PFNGLPROGRAMUNIFORM1DPROC = Option<unsafe extern "C" fn(program: GLuint, location: GLint, x: GLdouble)>;
enum PFNGLPROGRAMUNIFORM1DPROC { None, Some(unsafe extern "C" fn(_: u32, _: i32, _: f64)), }
No value.
Some value of type T.
T