Should the return types of the two versions be the same? If I make the non-segmented return sth like `typename util::detail::algorithm_result<ExPolicy,
            util::in_out_result<FwdIter1B, FwdIter2>>::type` while the segmented one returns a `typename util::detail::algorithm_result<ExPolicy,
            hpx::util::tagged_pair<tag::in(FwdIter1B),
                tag::out(FwdIter2)>>::type`