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