Non-empty vectors (vec1)

See the official docs for more info.

Why do we use Vec1 instead of Vec? Can't we just assume that all our vectors are not empty? Well, we could, but then:

1. We'd probably be wrong at some point in the future;

2. We're making the code inject panic code somewhere it probably doesn't need to; and

3. We can do better than this.

This article, although catered for Haskell, presents the case well. Put simply, if we require something to be non-empty, then we can express that with a type, and this means we don't need to re-validate its non-empty-ness after its creation.

We can also avoid using Vec by using Option<Vec1>; we still need to check whether we have Some or None, but doing so is better than assuming a Vec is non-empty.