pub fn unordered_hashcmp<'a, K: Hash + Clone + PartialEq + Eq + 'a, V: Clone + PartialEq + Debug + 'a, B: Iterator<Item = (&'a K, &'a V)>>(
    previous: B,
    current: B,
    key_only: bool
) -> Option<UnorderedMapLikeDiff<&'a K, &'a V>>