ranges_util.h

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// Utilities for representing and manipulating ranges -*- C++ -*-
 
// Copyright (C) 2019-2022 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.
 
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
 
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.
 
/** @file bits/ranges_util.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{ranges}
 */
 
#ifndef _RANGES_UTIL_H
#define _RANGES_UTIL_H 1
 
#if __cplusplus > 201703L
# include <bits/ranges_base.h>
# include <bits/utility.h>
 
#ifdef __cpp_lib_ranges
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
namespace ranges
{
  // C++20 24.5 [range.utility] Range utilities
 
  namespace __detail
  {
    template<typename _Range>
      concept __simple_view = view<_Range> && range<const _Range>
        && same_as<iterator_t<_Range>, iterator_t<const _Range>>
        && same_as<sentinel_t<_Range>, sentinel_t<const _Range>>;
 
    template<typename _It>
      concept __has_arrow = input_iterator<_It>
        && (is_pointer_v<_It> || requires(_It __it) { __it.operator->(); });
 
    template<typename _Tp, typename _Up>
      concept __different_from
        = !same_as<remove_cvref_t<_Tp>, remove_cvref_t<_Up>>;
  } // namespace __detail
 
  /// The ranges::view_interface class template
  template<typename _Derived>
    requires is_class_v<_Derived> && same_as<_Derived, remove_cv_t<_Derived>>
    class view_interface
    {
    private:
      constexpr _Derived& _M_derived() noexcept
      {
        static_assert(derived_from<_Derived, view_interface<_Derived>>);
        static_assert(view<_Derived>);
        return static_cast<_Derived&>(*this);
      }
 
      constexpr const _Derived& _M_derived() const noexcept
      {
        static_assert(derived_from<_Derived, view_interface<_Derived>>);
        static_assert(view<_Derived>);
        return static_cast<const _Derived&>(*this);
      }
 
      static constexpr bool
      _S_bool(bool) noexcept; // not defined
 
      template<typename _Tp>
        static constexpr bool
        _S_empty(_Tp& __t)
        noexcept(noexcept(_S_bool(ranges::begin(__t) == ranges::end(__t))))
        { return ranges::begin(__t) == ranges::end(__t); }
 
      template<typename _Tp>
        static constexpr auto
        _S_size(_Tp& __t)
        noexcept(noexcept(ranges::end(__t) - ranges::begin(__t)))
        { return ranges::end(__t) - ranges::begin(__t); }
 
    public:
      constexpr bool
      empty()
      noexcept(noexcept(_S_empty(_M_derived())))
      requires forward_range<_Derived>
      { return _S_empty(_M_derived()); }
 
      constexpr bool
      empty() const
      noexcept(noexcept(_S_empty(_M_derived())))
      requires forward_range<const _Derived>
      { return _S_empty(_M_derived()); }
 
      constexpr explicit
      operator bool() noexcept(noexcept(ranges::empty(_M_derived())))
      requires requires { ranges::empty(_M_derived()); }
      { return !ranges::empty(_M_derived()); }
 
      constexpr explicit
      operator bool() const noexcept(noexcept(ranges::empty(_M_derived())))
      requires requires { ranges::empty(_M_derived()); }
      { return !ranges::empty(_M_derived()); }
 
      constexpr auto
      data() noexcept(noexcept(ranges::begin(_M_derived())))
      requires contiguous_iterator<iterator_t<_Derived>>
      { return std::to_address(ranges::begin(_M_derived())); }
 
      constexpr auto
      data() const noexcept(noexcept(ranges::begin(_M_derived())))
      requires range<const _Derived>
        && contiguous_iterator<iterator_t<const _Derived>>
      { return std::to_address(ranges::begin(_M_derived())); }
 
      constexpr auto
      size() noexcept(noexcept(_S_size(_M_derived())))
      requires forward_range<_Derived>
        && sized_sentinel_for<sentinel_t<_Derived>, iterator_t<_Derived>>
      { return _S_size(_M_derived()); }
 
      constexpr auto
      size() const noexcept(noexcept(_S_size(_M_derived())))
      requires forward_range<const _Derived>
        && sized_sentinel_for<sentinel_t<const _Derived>,
                              iterator_t<const _Derived>>
      { return _S_size(_M_derived()); }
 
      constexpr decltype(auto)
      front() requires forward_range<_Derived>
      {
        __glibcxx_assert(!empty());
        return *ranges::begin(_M_derived());
      }
 
      constexpr decltype(auto)
      front() const requires forward_range<const _Derived>
      {
        __glibcxx_assert(!empty());
        return *ranges::begin(_M_derived());
      }
 
      constexpr decltype(auto)
      back()
      requires bidirectional_range<_Derived> && common_range<_Derived>
      {
        __glibcxx_assert(!empty());
        return *ranges::prev(ranges::end(_M_derived()));
      }
 
      constexpr decltype(auto)
      back() const
      requires bidirectional_range<const _Derived>
        && common_range<const _Derived>
      {
        __glibcxx_assert(!empty());
        return *ranges::prev(ranges::end(_M_derived()));
      }
 
      template<random_access_range _Range = _Derived>
        constexpr decltype(auto)
        operator[](range_difference_t<_Range> __n)
        { return ranges::begin(_M_derived())[__n]; }
 
      template<random_access_range _Range = const _Derived>
        constexpr decltype(auto)
        operator[](range_difference_t<_Range> __n) const
        { return ranges::begin(_M_derived())[__n]; }
    };
 
  namespace __detail
  {
    template<typename _From, typename _To>
      concept __uses_nonqualification_pointer_conversion
        = is_pointer_v<_From> && is_pointer_v<_To>
          && !convertible_to<remove_pointer_t<_From>(*)[],
                             remove_pointer_t<_To>(*)[]>;
 
    template<typename _From, typename _To>
      concept __convertible_to_non_slicing = convertible_to<_From, _To>
        && !__uses_nonqualification_pointer_conversion<decay_t<_From>,
                                                       decay_t<_To>>;
 
    template<typename _Tp>
      concept __pair_like
        = !is_reference_v<_Tp> && requires(_Tp __t)
        {
          typename tuple_size<_Tp>::type;
          requires derived_from<tuple_size<_Tp>, integral_constant<size_t, 2>>;
          typename tuple_element_t<0, remove_const_t<_Tp>>;
          typename tuple_element_t<1, remove_const_t<_Tp>>;
          { get<0>(__t) } -> convertible_to<const tuple_element_t<0, _Tp>&>;
          { get<1>(__t) } -> convertible_to<const tuple_element_t<1, _Tp>&>;
        };
 
    template<typename _Tp, typename _Up, typename _Vp>
      concept __pair_like_convertible_from
        = !range<_Tp> && __pair_like<_Tp>
        && constructible_from<_Tp, _Up, _Vp>
        && __convertible_to_non_slicing<_Up, tuple_element_t<0, _Tp>>
        && convertible_to<_Vp, tuple_element_t<1, _Tp>>;
 
  } // namespace __detail
 
  namespace views { struct _Drop; } // defined in <ranges>
 
  enum class subrange_kind : bool { unsized, sized };
 
  /// The ranges::subrange class template
  template<input_or_output_iterator _It, sentinel_for<_It> _Sent = _It,
           subrange_kind _Kind = sized_sentinel_for<_Sent, _It>
             ? subrange_kind::sized : subrange_kind::unsized>
    requires (_Kind == subrange_kind::sized || !sized_sentinel_for<_Sent, _It>)
    class subrange : public view_interface<subrange<_It, _Sent, _Kind>>
    {
    private:
      static constexpr bool _S_store_size
        = _Kind == subrange_kind::sized && !sized_sentinel_for<_Sent, _It>;
 
      friend struct views::_Drop; // Needs to inspect _S_store_size.
 
      _It _M_begin = _It();
      [[no_unique_address]] _Sent _M_end = _Sent();
 
      using __size_type
        = __detail::__make_unsigned_like_t<iter_difference_t<_It>>;
 
      template<typename, bool = _S_store_size>
        struct _Size
        { };
 
      template<typename _Tp>
        struct _Size<_Tp, true>
        { _Tp _M_size; };
 
      [[no_unique_address]] _Size<__size_type> _M_size = {};
 
    public:
      subrange() requires default_initializable<_It> = default;
 
      constexpr
      subrange(__detail::__convertible_to_non_slicing<_It> auto __i, _Sent __s)
      noexcept(is_nothrow_constructible_v<_It, decltype(__i)>
               && is_nothrow_constructible_v<_Sent, _Sent&>)
        requires (!_S_store_size)
      : _M_begin(std::move(__i)), _M_end(__s)
      { }
 
      constexpr
      subrange(__detail::__convertible_to_non_slicing<_It> auto __i, _Sent __s,
               __size_type __n)
      noexcept(is_nothrow_constructible_v<_It, decltype(__i)>
               && is_nothrow_constructible_v<_Sent, _Sent&>)
        requires (_Kind == subrange_kind::sized)
      : _M_begin(std::move(__i)), _M_end(__s)
      {
        if constexpr (_S_store_size)
          _M_size._M_size = __n;
      }
 
      template<__detail::__different_from<subrange> _Rng>
        requires borrowed_range<_Rng>
          && __detail::__convertible_to_non_slicing<iterator_t<_Rng>, _It>
          && convertible_to<sentinel_t<_Rng>, _Sent>
        constexpr
        subrange(_Rng&& __r)
        noexcept(noexcept(subrange(__r, ranges::size(__r))))
        requires _S_store_size && sized_range<_Rng>
        : subrange(__r, ranges::size(__r))
        { }
 
      template<__detail::__different_from<subrange> _Rng>
        requires borrowed_range<_Rng>
          && __detail::__convertible_to_non_slicing<iterator_t<_Rng>, _It>
          && convertible_to<sentinel_t<_Rng>, _Sent>
        constexpr
        subrange(_Rng&& __r)
        noexcept(noexcept(subrange(ranges::begin(__r), ranges::end(__r))))
        requires (!_S_store_size)
        : subrange(ranges::begin(__r), ranges::end(__r))
        { }
 
      template<borrowed_range _Rng>
        requires __detail::__convertible_to_non_slicing<iterator_t<_Rng>, _It>
          && convertible_to<sentinel_t<_Rng>, _Sent>
        constexpr
        subrange(_Rng&& __r, __size_type __n)
        noexcept(noexcept(subrange(ranges::begin(__r), ranges::end(__r), __n)))
        requires (_Kind == subrange_kind::sized)
        : subrange{ranges::begin(__r), ranges::end(__r), __n}
        { }
 
      template<__detail::__different_from<subrange> _PairLike>
        requires __detail::__pair_like_convertible_from<_PairLike, const _It&,
                                                        const _Sent&>
        constexpr
        operator _PairLike() const
        { return _PairLike(_M_begin, _M_end); }
 
      constexpr _It
      begin() const requires copyable<_It>
      { return _M_begin; }
 
      [[nodiscard]] constexpr _It
      begin() requires (!copyable<_It>)
      { return std::move(_M_begin); }
 
      constexpr _Sent end() const { return _M_end; }
 
      constexpr bool empty() const { return _M_begin == _M_end; }
 
      constexpr __size_type
      size() const requires (_Kind == subrange_kind::sized)
      {
        if constexpr (_S_store_size)
          return _M_size._M_size;
        else
          return __detail::__to_unsigned_like(_M_end - _M_begin);
      }
 
      [[nodiscard]] constexpr subrange
      next(iter_difference_t<_It> __n = 1) const &
        requires forward_iterator<_It>
      {
        auto __tmp = *this;
        __tmp.advance(__n);
        return __tmp;
      }
 
      [[nodiscard]] constexpr subrange
      next(iter_difference_t<_It> __n = 1) &&
      {
        advance(__n);
        return std::move(*this);
      }
 
      [[nodiscard]] constexpr subrange
      prev(iter_difference_t<_It> __n = 1) const
        requires bidirectional_iterator<_It>
      {
        auto __tmp = *this;
        __tmp.advance(-__n);
        return __tmp;
      }
 
      constexpr subrange&
      advance(iter_difference_t<_It> __n)
      {
        // _GLIBCXX_RESOLVE_LIB_DEFECTS
        // 3433. subrange::advance(n) has UB when n < 0
        if constexpr (bidirectional_iterator<_It>)
          if (__n < 0)
            {
              ranges::advance(_M_begin, __n);
              if constexpr (_S_store_size)
                _M_size._M_size += __detail::__to_unsigned_like(-__n);
              return *this;
            }
 
        __glibcxx_assert(__n >= 0);
        auto __d = __n - ranges::advance(_M_begin, __n, _M_end);
        if constexpr (_S_store_size)
          _M_size._M_size -= __detail::__to_unsigned_like(__d);
        return *this;
      }
    };
 
  template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
    subrange(_It, _Sent) -> subrange<_It, _Sent>;
 
  template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
    subrange(_It, _Sent,
             __detail::__make_unsigned_like_t<iter_difference_t<_It>>)
      -> subrange<_It, _Sent, subrange_kind::sized>;
 
  template<borrowed_range _Rng>
    subrange(_Rng&&)
      -> subrange<iterator_t<_Rng>, sentinel_t<_Rng>,
                 (sized_range<_Rng>
                  || sized_sentinel_for<sentinel_t<_Rng>, iterator_t<_Rng>>)
                 ? subrange_kind::sized : subrange_kind::unsized>;
 
  template<borrowed_range _Rng>
    subrange(_Rng&&,
             __detail::__make_unsigned_like_t<range_difference_t<_Rng>>)
      -> subrange<iterator_t<_Rng>, sentinel_t<_Rng>, subrange_kind::sized>;
 
  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // 3589. The const lvalue reference overload of get for subrange does not
  // constrain I to be copyable when N == 0
  template<size_t _Num, class _It, class _Sent, subrange_kind _Kind>
    requires ((_Num == 0 && copyable<_It>) || _Num == 1)
    constexpr auto
    get(const subrange<_It, _Sent, _Kind>& __r)
    {
      if constexpr (_Num == 0)
        return __r.begin();
      else
        return __r.end();
    }
 
  template<size_t _Num, class _It, class _Sent, subrange_kind _Kind>
    requires (_Num < 2)
    constexpr auto
    get(subrange<_It, _Sent, _Kind>&& __r)
    {
      if constexpr (_Num == 0)
        return __r.begin();
      else
        return __r.end();
    }
 
  template<typename _It, typename _Sent, subrange_kind _Kind>
    inline constexpr bool
      enable_borrowed_range<subrange<_It, _Sent, _Kind>> = true;
 
  template<range _Range>
    using borrowed_subrange_t = __conditional_t<borrowed_range<_Range>,
                                                subrange<iterator_t<_Range>>,
                                                dangling>;
} // namespace ranges
 
// The following ranges algorithms are used by <ranges>, and are defined here
// so that <ranges> can avoid including all of <bits/ranges_algo.h>.
namespace ranges
{
  struct __find_fn
  {
    template<input_iterator _Iter, sentinel_for<_Iter> _Sent, typename _Tp,
             typename _Proj = identity>
      requires indirect_binary_predicate<ranges::equal_to,
                                         projected<_Iter, _Proj>, const _Tp*>
      constexpr _Iter
      operator()(_Iter __first, _Sent __last,
                 const _Tp& __value, _Proj __proj = {}) const
      {
        while (__first != __last
            && !(std::__invoke(__proj, *__first) == __value))
          ++__first;
        return __first;
      }
 
    template<input_range _Range, typename _Tp, typename _Proj = identity>
      requires indirect_binary_predicate<ranges::equal_to,
                                         projected<iterator_t<_Range>, _Proj>,
                                         const _Tp*>
      constexpr borrowed_iterator_t<_Range>
      operator()(_Range&& __r, const _Tp& __value, _Proj __proj = {}) const
      {
        return (*this)(ranges::begin(__r), ranges::end(__r),
                       __value, std::move(__proj));
      }
  };
 
  inline constexpr __find_fn find{};
 
  struct __find_if_fn
  {
    template<input_iterator _Iter, sentinel_for<_Iter> _Sent,
             typename _Proj = identity,
             indirect_unary_predicate<projected<_Iter, _Proj>> _Pred>
      constexpr _Iter
      operator()(_Iter __first, _Sent __last,
                 _Pred __pred, _Proj __proj = {}) const
      {
        while (__first != __last
            && !(bool)std::__invoke(__pred, std::__invoke(__proj, *__first)))
          ++__first;
        return __first;
      }
 
    template<input_range _Range, typename _Proj = identity,
             indirect_unary_predicate<projected<iterator_t<_Range>, _Proj>>
               _Pred>
      constexpr borrowed_iterator_t<_Range>
      operator()(_Range&& __r, _Pred __pred, _Proj __proj = {}) const
      {
        return (*this)(ranges::begin(__r), ranges::end(__r),
                       std::move(__pred), std::move(__proj));
      }
  };
 
  inline constexpr __find_if_fn find_if{};
 
  struct __find_if_not_fn
  {
    template<input_iterator _Iter, sentinel_for<_Iter> _Sent,
             typename _Proj = identity,
             indirect_unary_predicate<projected<_Iter, _Proj>> _Pred>
      constexpr _Iter
      operator()(_Iter __first, _Sent __last,
                 _Pred __pred, _Proj __proj = {}) const
      {
        while (__first != __last
            && (bool)std::__invoke(__pred, std::__invoke(__proj, *__first)))
          ++__first;
        return __first;
      }
 
    template<input_range _Range, typename _Proj = identity,
             indirect_unary_predicate<projected<iterator_t<_Range>, _Proj>>
               _Pred>
      constexpr borrowed_iterator_t<_Range>
      operator()(_Range&& __r, _Pred __pred, _Proj __proj = {}) const
      {
        return (*this)(ranges::begin(__r), ranges::end(__r),
                       std::move(__pred), std::move(__proj));
      }
  };
 
  inline constexpr __find_if_not_fn find_if_not{};
 
  template<typename _Iter1, typename _Iter2>
    struct in_in_result
    {
      [[no_unique_address]] _Iter1 in1;
      [[no_unique_address]] _Iter2 in2;
 
      template<typename _IIter1, typename _IIter2>
        requires convertible_to<const _Iter1&, _IIter1>
          && convertible_to<const _Iter2&, _IIter2>
        constexpr
        operator in_in_result<_IIter1, _IIter2>() const &
        { return {in1, in2}; }
 
      template<typename _IIter1, typename _IIter2>
        requires convertible_to<_Iter1, _IIter1>
          && convertible_to<_Iter2, _IIter2>
        constexpr
        operator in_in_result<_IIter1, _IIter2>() &&
        { return {std::move(in1), std::move(in2)}; }
    };
 
  template<typename _Iter1, typename _Iter2>
    using mismatch_result = in_in_result<_Iter1, _Iter2>;
 
  struct __mismatch_fn
  {
    template<input_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
             input_iterator _Iter2, sentinel_for<_Iter2> _Sent2,
             typename _Pred = ranges::equal_to,
             typename _Proj1 = identity, typename _Proj2 = identity>
      requires indirectly_comparable<_Iter1, _Iter2, _Pred, _Proj1, _Proj2>
      constexpr mismatch_result<_Iter1, _Iter2>
      operator()(_Iter1 __first1, _Sent1 __last1,
                 _Iter2 __first2, _Sent2 __last2, _Pred __pred = {},
                 _Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
      {
        while (__first1 != __last1 && __first2 != __last2
               && (bool)std::__invoke(__pred,
                                      std::__invoke(__proj1, *__first1),
                                      std::__invoke(__proj2, *__first2)))
        {
          ++__first1;
          ++__first2;
        }
        return { std::move(__first1), std::move(__first2) };
      }
 
    template<input_range _Range1, input_range _Range2,
             typename _Pred = ranges::equal_to,
             typename _Proj1 = identity, typename _Proj2 = identity>
      requires indirectly_comparable<iterator_t<_Range1>, iterator_t<_Range2>,
                                     _Pred, _Proj1, _Proj2>
      constexpr mismatch_result<iterator_t<_Range1>, iterator_t<_Range2>>
      operator()(_Range1&& __r1, _Range2&& __r2, _Pred __pred = {},
                 _Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
      {
        return (*this)(ranges::begin(__r1), ranges::end(__r1),
                       ranges::begin(__r2), ranges::end(__r2),
                       std::move(__pred),
                       std::move(__proj1), std::move(__proj2));
      }
  };
 
  inline constexpr __mismatch_fn mismatch{};
 
  struct __search_fn
  {
    template<forward_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
             forward_iterator _Iter2, sentinel_for<_Iter2> _Sent2,
             typename _Pred = ranges::equal_to,
             typename _Proj1 = identity, typename _Proj2 = identity>
      requires indirectly_comparable<_Iter1, _Iter2, _Pred, _Proj1, _Proj2>
      constexpr subrange<_Iter1>
      operator()(_Iter1 __first1, _Sent1 __last1,
                 _Iter2 __first2, _Sent2 __last2, _Pred __pred = {},
                 _Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
      {
        if (__first1 == __last1 || __first2 == __last2)
          return {__first1, __first1};
 
        for (;;)
          {
            for (;;)
              {
                if (__first1 == __last1)
                  return {__first1, __first1};
                if (std::__invoke(__pred,
                                  std::__invoke(__proj1, *__first1),
                                  std::__invoke(__proj2, *__first2)))
                  break;
                ++__first1;
              }
            auto __cur1 = __first1;
            auto __cur2 = __first2;
            for (;;)
              {
                if (++__cur2 == __last2)
                  return {__first1, ++__cur1};
                if (++__cur1 == __last1)
                  return {__cur1, __cur1};
                if (!(bool)std::__invoke(__pred,
                                         std::__invoke(__proj1, *__cur1),
                                         std::__invoke(__proj2, *__cur2)))
                  {
                    ++__first1;
                    break;
                  }
              }
          }
      }
 
    template<forward_range _Range1, forward_range _Range2,
             typename _Pred = ranges::equal_to,
             typename _Proj1 = identity, typename _Proj2 = identity>
      requires indirectly_comparable<iterator_t<_Range1>, iterator_t<_Range2>,
                                     _Pred, _Proj1, _Proj2>
      constexpr borrowed_subrange_t<_Range1>
      operator()(_Range1&& __r1, _Range2&& __r2, _Pred __pred = {},
                 _Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
      {
        return (*this)(ranges::begin(__r1), ranges::end(__r1),
                       ranges::begin(__r2), ranges::end(__r2),
                       std::move(__pred),
                       std::move(__proj1), std::move(__proj2));
      }
  };
 
  inline constexpr __search_fn search{};
} // namespace ranges
 
  using ranges::get;
 
  template<typename _Iter, typename _Sent, ranges::subrange_kind _Kind>
    struct tuple_size<ranges::subrange<_Iter, _Sent, _Kind>>
    : integral_constant<size_t, 2>
    { };
 
  template<typename _Iter, typename _Sent, ranges::subrange_kind _Kind>
    struct tuple_element<0, ranges::subrange<_Iter, _Sent, _Kind>>
    { using type = _Iter; };
 
  template<typename _Iter, typename _Sent, ranges::subrange_kind _Kind>
    struct tuple_element<1, ranges::subrange<_Iter, _Sent, _Kind>>
    { using type = _Sent; };
 
  template<typename _Iter, typename _Sent, ranges::subrange_kind _Kind>
    struct tuple_element<0, const ranges::subrange<_Iter, _Sent, _Kind>>
    { using type = _Iter; };
 
  template<typename _Iter, typename _Sent, ranges::subrange_kind _Kind>
    struct tuple_element<1, const ranges::subrange<_Iter, _Sent, _Kind>>
    { using type = _Sent; };
 
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // library concepts
#endif // C++20
#endif // _RANGES_UTIL_H