pub type dnormfv_ft = Option<unsafe extern "C" fn(n: dim_t, x: *mut f64, incx: inc_t, norm: *mut f64)>;
enum dnormfv_ft { None, Some(unsafe extern "C" fn(_: i64, _: *mut f64, _: i64, _: *mut f64)), }
No value.
Some value of type T.
T