Comment by kbolino

There is a middle ground that I think the post glosses over, which would be to split apart the Result<T,E> value whenever its two cases differ significantly in size. You'd also have to track the discriminant of course.

Basically, supposing T alone fits in a register or two, but E is so big that the union of T and E would spill onto the stack, treat them as two different values instead of one.