Re: [PATCH] libstdc++: Implement missing P0896 changes to reverse_view [PR100639]

[Patrick Palka <ppalka@redhat.com>]

On Tue, 18 May 2021, Patrick Palka wrote:

> This implements the P0896 changes to reverse_view's member types

Whoops, s/reverse_view/reverse_iterator rather... consider this typo
fixed throughout.

> value_type, difference_type and reference in C++20 mode, which fixes
> problems taking the reverse_iterator of an iterator with a non-integral
> difference_type (such as iota_view<long long>).
> 
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk and perhaps
> 10/11?
> 
> libstdc++-v3/ChangeLog:
> 
> 	PR libstdc++/100639
> 	* include/bits/stl_iterator.h (reverse_view::difference_type):
> 	In C++20 mode, define in terms of iter_difference_t as per P0896.
> 	(reverse_view::reference): Likewise, but with iter_reference_t.
> 	(reverse_view::value_type): Likewise, but with iter_value_t.
> 	* testsuite/std/ranges/adaptors/reverse.cc (test08): New test.
> 	* testsuite/24_iterators/reverse_iterator/100639.cc: New test.
> ---
>  libstdc++-v3/include/bits/stl_iterator.h      |  9 +++--
>  .../24_iterators/reverse_iterator/100639.cc   | 37 +++++++++++++++++++
>  .../testsuite/std/ranges/adaptors/reverse.cc  | 12 ++++++
>  3 files changed, 55 insertions(+), 3 deletions(-)
>  create mode 100644 libstdc++-v3/testsuite/24_iterators/reverse_iterator/100639.cc
> 
> diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
> index 2409cd71f86..8768624b7d1 100644
> --- a/libstdc++-v3/include/bits/stl_iterator.h
> +++ b/libstdc++-v3/include/bits/stl_iterator.h
> @@ -149,11 +149,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>  
>      public:
>        typedef _Iterator					iterator_type;
> -      typedef typename __traits_type::difference_type	difference_type;
>        typedef typename __traits_type::pointer		pointer;
> +#if __cplusplus <= 201703L
> +      typedef typename __traits_type::difference_type	difference_type;
>        typedef typename __traits_type::reference		reference;
> -
> -#if __cplusplus > 201703L && __cpp_lib_concepts
> +#else
>        using iterator_concept
>  	= conditional_t<random_access_iterator<_Iterator>,
>  			random_access_iterator_tag,
> @@ -161,6 +161,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>        using iterator_category
>  	= __detail::__clamp_iter_cat<typename __traits_type::iterator_category,
>  				     random_access_iterator_tag>;
> +      using value_type = iter_value_t<_Iterator>;
> +      using difference_type = iter_difference_t<_Iterator>;
> +      using reference = iter_reference_t<_Iterator>;
>  #endif
>  
>        /**
> diff --git a/libstdc++-v3/testsuite/24_iterators/reverse_iterator/100639.cc b/libstdc++-v3/testsuite/24_iterators/reverse_iterator/100639.cc
> new file mode 100644
> index 00000000000..358d91dfef1
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/24_iterators/reverse_iterator/100639.cc
> @@ -0,0 +1,37 @@
> +// Copyright (C) 2021 Free Software Foundation, Inc.
> +//
> +// This file is part of the GNU ISO C++ Library.  This library is free
> +// software; you can redistribute it and/or modify it under the
> +// terms of the GNU General Public License as published by the
> +// Free Software Foundation; either version 3, or (at your option)
> +// any later version.
> +
> +// This library is distributed in the hope that it will be useful,
> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +// GNU General Public License for more details.
> +
> +// You should have received a copy of the GNU General Public License along
> +// with this library; see the file COPYING3.  If not see
> +// <http://www.gnu.org/licenses/>.
> +
> +// { dg-options "-std=c++2a" }
> +// { dg-do compile { target c++2a } }
> +
> +// PR libstdc++/100639
> +
> +#include <iterator>
> +#include <ranges>
> +
> +void
> +test01()
> +{
> +  using iter = std::ranges::iterator_t<std::ranges::iota_view<long long>>;
> +  using riter = std::reverse_iterator<iter>;
> +  static_assert(std::same_as<std::iter_reference_t<iter>,
> +			     std::iter_reference_t<riter>>);
> +  static_assert(std::same_as<std::iter_value_t<iter>,
> +			     std::iter_value_t<riter>>);
> +  static_assert(std::same_as<std::iter_difference_t<iter>,
> +			     std::iter_difference_t<riter>>);
> +}
> diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/reverse.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/reverse.cc
> index 47e34eb6581..7f1bde1d5d5 100644
> --- a/libstdc++-v3/testsuite/std/ranges/adaptors/reverse.cc
> +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/reverse.cc
> @@ -161,6 +161,17 @@ test07()
>    static_assert(!requires { 0 | reverse; });
>  }
>  
> +void
> +test08()
> +{
> +  // PR libstdc++/100639
> +  for (auto val
> +       : views::iota(1701ll, 3000ll)
> +       | views::reverse
> +       | views::take(5))
> +    ;
> +}
> +
>  int
>  main()
>  {
> @@ -171,4 +182,5 @@ main()
>    test05();
>    test06();
>    test07();
> +  test08();
>  }
> -- 
> 2.32.0.rc0
> 
>