Re: [committed] libstdc++: Use alias template for iterator_category [PR110970]

[Jonathan Wakely <jwakely@redhat.com>]

[-- Attachment #1: Type: text/plain, Size: 5111 bytes --]

On Thu, 10 Aug 2023 at 23:34, Jonathan Wakely via Libstdc++ <
libstdc++@gcc.gnu.org> wrote:

> Tested x86_64-linux. Pushed to trunk. Backport to gcc-13 to follow.
>
> -- >8 --
>
> This renames __iterator_category_t to __iter_category_t, for consistency
> with std::iter_value_t, std::iter_difference_t and std::iter_reference_t
> in C++20. Then use __iter_category_t in <bits/stl_iterator.h>, which
> fixes the problem of the missing 'typename' that Clang 15 incorrectly
> still requires.
>
> libstdc++-v3/ChangeLog:
>
>         PR libstdc++/110970
>         * include/bits/stl_iterator.h (__detail::__move_iter_cat): Use
>         __iter_category_t.
>         (iterator_traits<common_iterator<I, S>>::_S_iter_cat): Likewise.
>         (__detail::__basic_const_iterator_iter_cat): Likewise.
>         * include/bits/stl_iterator_base_types.h (__iterator_category_t):
>         Rename to __iter_category_t.
> ---
>  libstdc++-v3/include/bits/stl_iterator.h        | 17 +++++++++--------
>  .../include/bits/stl_iterator_base_types.h      |  6 +++---
>  2 files changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/stl_iterator.h
> b/libstdc++-v3/include/bits/stl_iterator.h
> index b22d9a4fdb3..d5ba05f3e22 100644
> --- a/libstdc++-v3/include/bits/stl_iterator.h
> +++ b/libstdc++-v3/include/bits/stl_iterator.h
> @@ -103,6 +103,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>        using __clamp_iter_cat
>         = __conditional_t<derived_from<_Cat, _Limit>, _Limit, _Otherwise>;
>
> +    template<typename _Iter, typename _Limit>
> +      using __clamped_iter_cat_t
> +       = __clamp_iter_cat<__iter_category_t<_Iter>, _Limit>;
> +
>      template<typename _Tp, typename _Up>
>        concept __different_from
>         = !same_as<remove_cvref_t<_Tp>, remove_cvref_t<_Up>>;
> @@ -168,8 +172,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>                           random_access_iterator_tag,
>                           bidirectional_iterator_tag>;
>        using iterator_category
> -       = __detail::__clamp_iter_cat<typename
> __traits_type::iterator_category,
> -                                    random_access_iterator_tag>;
> +       = __detail::__clamped_iter_cat_t<_Iterator,
> random_access_iterator_tag>;
>        using value_type = iter_value_t<_Iterator>;
>        using difference_type = iter_difference_t<_Iterator>;
>        using reference = iter_reference_t<_Iterator>;
> @@ -1426,12 +1429,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>        { };
>
>      template<typename _Iterator>
> -      requires requires { typename
> iterator_traits<_Iterator>::iterator_category; }
> +      requires requires { typename __iter_category_t<_Iterator>; }
>        struct __move_iter_cat<_Iterator>
>        {
>         using iterator_category
> -         = __clamp_iter_cat<typename
> iterator_traits<_Iterator>::iterator_category,
> -                            random_access_iterator_tag>;
> +         = __clamped_iter_cat_t<_Iterator, random_access_iterator_tag>;
>

Oops, I only meant to commit the change to use __iter_category_t, not the
addition of __clamped_iter_cat. I'll revert that part. It was an experiment
that I decided against, and I thought I'd already reverted before
committing.




>        };
>  #endif
>    }
> @@ -2288,8 +2290,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>        static auto
>        _S_iter_cat()
>        {
> -       using _Traits = iterator_traits<_It>;
> -       if constexpr (requires { requires derived_from<typename
> _Traits::iterator_category,
> +       if constexpr (requires { requires
> derived_from<__iter_category_t<_It>,
>
>  forward_iterator_tag>; })
>           return forward_iterator_tag{};
>         else
> @@ -2615,7 +2616,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
>      template<forward_iterator _It>
>        struct __basic_const_iterator_iter_cat<_It>
> -      { using iterator_category =
> iterator_traits<_It>::iterator_category; };
> +      { using iterator_category = __iter_category_t<_It>; };
>    } // namespace detail
>
>    template<input_iterator _It>
> diff --git a/libstdc++-v3/include/bits/stl_iterator_base_types.h
> b/libstdc++-v3/include/bits/stl_iterator_base_types.h
> index 5d2c8b325d9..841b5eca3ad 100644
> --- a/libstdc++-v3/include/bits/stl_iterator_base_types.h
> +++ b/libstdc++-v3/include/bits/stl_iterator_base_types.h
> @@ -243,16 +243,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
>  #if __cplusplus >= 201103L
>    template<typename _Iter>
> -    using __iterator_category_t
> +    using __iter_category_t
>        = typename iterator_traits<_Iter>::iterator_category;
>
>    template<typename _InIter>
>      using _RequireInputIter =
> -      __enable_if_t<is_convertible<__iterator_category_t<_InIter>,
> +      __enable_if_t<is_convertible<__iter_category_t<_InIter>,
>                                    input_iterator_tag>::value>;
>
>    template<typename _It,
> -          typename _Cat = __iterator_category_t<_It>>
> +          typename _Cat = __iter_category_t<_It>>
>      struct __is_random_access_iter
>        : is_base_of<random_access_iterator_tag, _Cat>
>      {
> --
> 2.41.0
>
>