On Tue, 18 Feb 2025 at 04:11, Patrick Palka <ppa...@redhat.com> wrote:
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
>
> -- >8 --
>
> The original implementation was accidentally based off of an older
> revision of the paper, P2542R7 instead of R8. As far as I can tell
> the only semantic change in the final revision is the relaxed
> constraints on the iterator's iter/sent operator- overloads.
>
> The revision also simplifies the concat_view::end wording via C++26
> pack indexing, which GCC 15 and Clang 19/20 implement so we can use
> it unconditionally here and remove the __last_is_common helper trait.
What about Clang 18 with -std=c++26?
I'd be OK with making the ranges_concat macro depend on the one for
pack indexing though.
As I noted in bugzilla, the conct_view::iterator type should be named _Iterator
>
> PR libstdc++/115209
>
> libstdc++-v3/ChangeLog:
>
> * include/std/ranges (__detail::__last_is_common): Remove.
> (__detail::__all_but_first_sized): New.
> (concat_view::end): Use C++26 pack indexing instead of
> __last_is_common as per P2542R8.
> (concat_view::iterator::operator-): Update constraints on
> iter/sent overloads as per P2542R7.
> ---
> libstdc++-v3/include/std/ranges | 38 ++++++++++++++-------------------
> 1 file changed, 16 insertions(+), 22 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
> index 5c795a90fbc..22e0c9cae44 100644
> --- a/libstdc++-v3/include/std/ranges
> +++ b/libstdc++-v3/include/std/ranges
> @@ -9683,12 +9683,8 @@ namespace ranges
> && __all_but_last_common<_Const, _Rs...>::value;
>
> template<typename _Range, typename... _Rs>
> - struct __last_is_common
> - { static inline constexpr bool value =
> __last_is_common<_Rs...>::value; };
> -
> - template<typename _Range>
> - struct __last_is_common<_Range>
> - { static inline constexpr bool value = common_range<_Range>; };
> + struct __all_but_first_sized
> + { static inline constexpr bool value = (sized_range<_Rs> && ...); };
> } // namespace __detail
>
> template<input_range... _Vs>
> @@ -9726,13 +9722,11 @@ namespace ranges
> constexpr auto
> end() requires (!(__detail::__simple_view<_Vs> && ...))
> {
> + constexpr auto __n = sizeof...(_Vs);
> if constexpr ((semiregular<iterator_t<_Vs>> && ...)
> - && __detail::__last_is_common<_Vs...>::value)
> - {
> - constexpr auto __n = sizeof...(_Vs);
> - return iterator<false>(this, in_place_index<__n - 1>,
> - ranges::end(std::get<__n - 1>(_M_views)));
> - }
> + && common_range<_Vs...[__n - 1]>)
> + return iterator<false>(this, in_place_index<__n - 1>,
> + ranges::end(std::get<__n - 1>(_M_views)));
> else
> return default_sentinel;
> }
> @@ -9740,13 +9734,11 @@ namespace ranges
> constexpr auto
> end() const requires (range<const _Vs> && ...) &&
> __detail::__concatable<const _Vs...>
> {
> + constexpr auto __n = sizeof...(_Vs);
> if constexpr ((semiregular<iterator_t<const _Vs>> && ...)
> - && __detail::__last_is_common<const _Vs...>::value)
> - {
> - constexpr auto __n = sizeof...(_Vs);
> - return iterator<true>(this, in_place_index<__n - 1>,
> - ranges::end(std::get<__n - 1>(_M_views)));
> - }
> + && common_range<const _Vs...[__n - 1]>)
> + return iterator<true>(this, in_place_index<__n - 1>,
> + ranges::end(std::get<__n - 1>(_M_views)));
> else
> return default_sentinel;
> }
> @@ -10128,8 +10120,9 @@ namespace ranges
>
> friend constexpr difference_type
> operator-(const iterator& __x, default_sentinel_t)
> - requires __detail::__concat_is_random_access<_Const, _Vs...>
> - && __detail::__last_is_common<__maybe_const_t<_Const, _Vs>...>::value
> + requires (sized_sentinel_for<sentinel_t<__maybe_const_t<_Const, _Vs>>,
> + iterator_t<__maybe_const_t<_Const, _Vs>>>
> && ...)
> + && __detail::__all_but_first_sized<__maybe_const_t<_Const,
> _Vs>...>::value
> {
> return _S_invoke_with_runtime_index([&]<size_t _Ix>() ->
> difference_type {
> auto __dx = ranges::distance(std::get<_Ix>(__x._M_it),
> @@ -10148,8 +10141,9 @@ namespace ranges
>
> friend constexpr difference_type
> operator-(default_sentinel_t, const iterator& __x)
> - requires __detail::__concat_is_random_access<_Const, _Vs...>
> - && __detail::__last_is_common<__maybe_const_t<_Const, _Vs>...>::value
> + requires (sized_sentinel_for<sentinel_t<__maybe_const_t<_Const, _Vs>>,
> + iterator_t<__maybe_const_t<_Const, _Vs>>>
> && ...)
> + && __detail::__all_but_first_sized<__maybe_const_t<_Const,
> _Vs>...>::value
> { return -(__x - default_sentinel); }
>
> friend constexpr decltype(auto)
> --
> 2.48.1.356.g0394451348.dirty
>
