The full-blown version that guarantees no bounds-check errors at runtime requires dependent types (and consequently requires programmers to work with a proof assistant, which is why it's not very popular). You could have a more lightweight version that instead just crashes the program at runtime if an out-of-range assignment is attempted, and optionally requires such fallible assignments to be marked as such in the code. Rust can do this today with const generics, though it's rather clunky as there's very little syntactic sugar and no implicit widening.