svoid mapMethodLike internByteArrayField(S field, Cl l) {
  HashMap<HashedByteArray, byte[]> map = new HashMap;
  fOr (O o : l) {
    byte[] value = cast getOpt(o, field);
    if (value == null) continue;
    HashedByteArray hashed = new(value);
    byte[] existing = map.get(hashed);
    if (existing != null)
      setOpt(o, field, existing);
    else
      map.put(hashed, value);
  }
}