My impression was that the discriminant would be "as if" it's there, but it wouldn't actually be allocated, or at least its allocation can be avoided if there i

My impression was that the discriminant would be "as if" it's there, but it wouldn't actually be allocated, or at least its allocation can be avoided if there is a sentinel success value for the error case (0 -> success, not-0 -> failure and the specific value indicates what type of failure).