trait Nat {
    const VALUE: usize;
}

struct Zero;

impl Nat for Zero {
    const VALUE: usize = 0;
}

struct Succ<K>(K);

impl<K: Nat> Nat for Succ<K> {
    const VALUE: usize = K::VALUE + 1;
}

fn foo<K>(fixed_size_arr: &[u32; <K as Nat>::VALUE]) -> usize
where
    K: Nat,
{
    fixed_size_arr.len()
}

fn main() {
    println!("{}", foo::<Zero>(&[]));
    println!("{}", foo::<Succ<Zero>>(&[0]));
    println!("{}", foo::<Succ<Succ<Zero>>>(&[0, 0]));
    println!("{}", foo::<Succ<Succ<Succ<Zero>>>>(&[0, 0, 0]));
}