@Override
    public boolean equals(@Nullable Object obj) {
      if (obj instanceof UsesReferentialEquality) {
        UsesReferentialEquality that = (UsesReferentialEquality) obj;
        return s == that.s;
      }
      return false;
    }
  }

  static class UsesEnum {
    private final TimeUnit s;

    public UsesEnum(TimeUnit s) {
      this.s = checkNotNull(s);
    }