Collecting iterators into arrays

[Centril]

@HadrienG

Hmmm…

Btw, here's a sketch I made a while ago,

Fixed-size lazy iterators?

I did some more thinking and came up with the following: // Machinery for type level if->0-then-else // It is a bit unfortunate that we need all this boilerplate. struct Nat<const N: usize>(PhantomData<[(); N]>); trait IfSuccFn<S, Z> { type Out; } // If Succ(N) => S impl<const N: usize, S, Z> IfSuccFn<S, Z> for Nat<{N + 1}> { type Out = S; } // If 0 => Z impl<S, Z> IfSuccFn<S, Z> for Nat<{0}> { type Out = Z; } // if N > 0 then S, else Z. type IfSucc<const N: usize, S, Z> = <Nat<N> as IfSucc<S, …