Would it be possible to have this as a freestanding function `fn make_hash<T: Hash>(k0: u64, k1: u64: t: &T) -> u64 { ... }` just to avoid the unnecessary code bloat (i.e. this will be instantiated for every `(K, V)` pair of types used with `HashMap`, and then again for every `(K, V, Equiv)` triple of types if any of the `...._equiv ` methods are used; but we only need it once for each `K` and once for each `Equiv`.)