On Tue, Mar 11, 2025 at 5:04 PM Patrick Palka <ppa...@redhat.com> wrote:

> On Tue, 11 Mar 2025, Tomasz Kaminski wrote:
>
> >
> >
> > On Mon, Mar 10, 2025 at 11:28 PM Patrick Palka <ppa...@redhat.com>
> wrote:
> >       Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
> >
> >       -- >8 --
> >
> >       libstdc++-v3/ChangeLog:
> >
> >               * include/bits/version.def (ranges_to_input): Define.
> >               * include/bits/version.h: Regenerate.
> >               * include/std/ranges (ranges::to_input_view): Define for
> C++26.
> >               (views::__detail::__can_to_input): Likewise.
> >               (views::_ToInput, views::to_input): Likewise.
> >               * testsuite/std/ranges/adaptors/to_input/1.cc: New test.
> >       ---
> >        libstdc++-v3/include/bits/version.def         |   8 +
> >        libstdc++-v3/include/bits/version.h           |  10 ++
> >        libstdc++-v3/include/std/ranges               | 170
> ++++++++++++++++++
> >        .../std/ranges/adaptors/to_input/1.cc         |  58 ++++++
> >        4 files changed, 246 insertions(+)
> >        create mode 100644
> libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc
> >
> >       diff --git a/libstdc++-v3/include/bits/version.def
> b/libstdc++-v3/include/bits/version.def
> >       index 2af5a54bff2..c2b5283df89 100644
> >       --- a/libstdc++-v3/include/bits/version.def
> >       +++ b/libstdc++-v3/include/bits/version.def
> >       @@ -1910,6 +1910,14 @@ ftms = {
> >          };
> >        };
> >
> >       +ftms = {
> >       +  name = ranges_to_input;
> >       +  values = {
> >       +    v = 202502;
> >       +    cxxmin = 26;
> >       +  };
> >       +};
> >       +
> >        ftms = {
> >          name = to_string;
> >          values = {
> >       diff --git a/libstdc++-v3/include/bits/version.h
> b/libstdc++-v3/include/bits/version.h
> >       index 9833023cfdc..775c8642139 100644
> >       --- a/libstdc++-v3/include/bits/version.h
> >       +++ b/libstdc++-v3/include/bits/version.h
> >       @@ -2120,6 +2120,16 @@
> >        #endif /* !defined(__cpp_lib_text_encoding) &&
> defined(__glibcxx_want_text_encoding) */
> >        #undef __glibcxx_want_text_encoding
> >
> >       +#if !defined(__cpp_lib_ranges_to_input)
> >       +# if (__cplusplus >  202302L)
> >       +#  define __glibcxx_ranges_to_input 202502L
> >       +#  if defined(__glibcxx_want_all) ||
> defined(__glibcxx_want_ranges_to_input)
> >       +#   define __cpp_lib_ranges_to_input 202502L
> >       +#  endif
> >       +# endif
> >       +#endif /* !defined(__cpp_lib_ranges_to_input) &&
> defined(__glibcxx_want_ranges_to_input) */
> >       +#undef __glibcxx_want_ranges_to_input
> >       +
> >        #if !defined(__cpp_lib_to_string)
> >        # if (__cplusplus >  202302L) && _GLIBCXX_HOSTED &&
> (__glibcxx_to_chars)
> >        #  define __glibcxx_to_string 202306L
> >       diff --git a/libstdc++-v3/include/std/ranges
> b/libstdc++-v3/include/std/ranges
> >       index e21f5284b46..dd97d276ef0 100644
> >       --- a/libstdc++-v3/include/std/ranges
> >       +++ b/libstdc++-v3/include/std/ranges
> >       @@ -69,6 +69,7 @@
> >        #define __glibcxx_want_ranges_slide
> >        #define __glibcxx_want_ranges_stride
> >        #define __glibcxx_want_ranges_to_container
> >       +#define __glibcxx_want_ranges_to_input
> >        #define __glibcxx_want_ranges_zip
> >        #include <bits/version.h>
> >
> >       @@ -10390,6 +10391,175 @@ namespace ranges
> >        } // namespace ranges
> >        #endif // __cpp_lib_ranges_cache_latest
> >
> >       +#if __cpp_lib_ranges_to_input // C++ >= 26
> >       +namespace ranges
> >       +{
> >       +  template<input_range _Vp>
> >       +    requires view<_Vp>
> >       +  class to_input_view : public view_interface<to_input_view<_Vp>>
> >       +  {
> >       +    _Vp _M_base = _Vp();
> >       +
> >       +    template<bool _Const>
> >       +    class _Iterator;
> >       +
> >       +  public:
> >       +    to_input_view() requires default_initializable<_Vp> = default;
> >       +
> >       +    constexpr explicit
> >       +    to_input_view(_Vp __base)
> >       +    : _M_base(std::move(__base))
> >       +    { }
> >       +
> >       +    constexpr _Vp
> >       +    base() const & requires copy_constructible<_Vp>
> >       +    { return _M_base; }
> >       +
> >       +    constexpr _Vp
> >       +    base() &&
> >       +    { return std::move(_M_base); }
> >       +
> >       +    constexpr auto
> >       +    begin() requires (!__detail::__simple_view<_Vp>)
> >       +    { return _Iterator<false>(ranges::begin(_M_base)); }
> >       +
> >       +    constexpr auto
> >       +    begin() const requires range<const _Vp>
> >       +    { return _Iterator<true>(ranges::begin(_M_base)); }
> >       +
> >       +    constexpr auto
> >       +    end() requires (!__detail::__simple_view<_Vp>)
> >       +    { return ranges::end(_M_base); }
> >       +
> >       +    constexpr auto
> >       +    end() const requires range<const _Vp>
> >       +    { return ranges::end(_M_base); }
> >       +
> >       +    constexpr auto
> >       +    size() requires sized_range<_Vp>
> >       +    { return ranges::size(_M_base); }
> >       +
> >       +    constexpr auto
> >       +    size() const requires sized_range<const _Vp>
> >       +    { return ranges::size(_M_base); }
> >       +  };
> >       +
> >       +  template<typename _Range>
> >       +    to_input_view(_Range&&) ->
> to_input_view<views::all_t<_Range>>;
> >       +
> >       +  template<input_range _Vp>
> >       +    requires view<_Vp>
> >       +  template<bool _Const>
> >       +  class to_input_view<_Vp>::_Iterator
> >       +  {
> >       +    using _Base = __maybe_const_t<_Const, _Vp>;
> >       +
> >       +    iterator_t<_Base> _M_current = iterator_t<_Base>();
> >       +
> >       +    constexpr explicit
> >       +    _Iterator(iterator_t<_Base> __current)
> >       +    : _M_current(std::move(__current))
> >       +    { }
> >       +
> >       +    friend to_input_view;
> >       +    friend _Iterator<!_Const>;
> >       +
> >       +  public:
> >       +    using difference_type = range_difference_t<_Base>;
> >       +    using value_type = range_value_t<_Base>;
> >       +    using iterator_concept = input_iterator_tag;
> >       +
> >       +    _Iterator() requires default_initializable<iterator_t<_Base>>
> = default;
> >       +
> >       +    _Iterator(_Iterator&&) = default;
> >       +    _Iterator& operator=(_Iterator&&) = default;
> >       +
> >       +    constexpr
> >       +    _Iterator(_Iterator<!_Const> __i)
> >       +      requires _Const && convertible_to<iterator_t<_Vp>,
> iterator_t<_Base>>
> >       +    : _M_current(std::move(__i._M_current))
> >       +    { }
> >       +
> >       +    constexpr iterator_t<_Base>
> >       +    base() &&
> >       +    { return std::move(_M_current); }
> >       +
> >       +    constexpr const iterator_t<_Base>&
> >       +    base() const & noexcept
> >       +    { return _M_current; }
> >       +
> >       +    constexpr decltype(auto)
> >       +    operator*() const
> >       +    { return *_M_current; }
> >       +
> >       +    constexpr _Iterator&
> >       +    operator++()
> >       +    {
> >       +      ++_M_current;
> >       +      return *this;
> >       +    }
> >       +
> >       +    constexpr void
> >       +    operator++(int)
> >       +    { ++*this; }
> >       +
> >       +    friend constexpr bool
> >       +    operator==(const _Iterator& __x, const sentinel_t<_Base>& __y)
> >       +    { return __x._M_current == __y; }
> >       +
> >       +    friend constexpr difference_type
> >       +    operator-(const sentinel_t<_Base>& __y, const _Iterator& __x)
> >       +      requires sized_sentinel_for<sentinel_t<_Base>,
> iterator_t<_Base>>
> >       +    { return __y - __x._M_current; }
> >       +
> >       +    friend constexpr difference_type
> >       +    operator-(const _Iterator& __x, const sentinel_t<_Base>& __y)
> >       +      requires sized_sentinel_for<sentinel_t<_Base>,
> iterator_t<_Base>>
> >       +    { return __x._M_current - __y; }
> >       +
> >       +    friend constexpr range_rvalue_reference_t<_Base>
> >       +    iter_move(const _Iterator& __i)
> >       +      noexcept(noexcept(ranges::iter_move(__i._M_current)))
> >       +    { return ranges::iter_move(__i._M_current); }
> >       +
> >       +    friend constexpr void
> >       +    iter_swap(const _Iterator& __x, const _Iterator& __y)
> >       +      noexcept(noexcept(ranges::iter_swap(__x._M_current,
> __y._M_current)))
> >       +      requires indirectly_swappable<iterator_t<_Base>>
> >       +    { ranges::iter_swap(__x._M_current, __y._M_current); }
> >       +  };
> >       +
> >       +  namespace views
> >       +  {
> >       +    namespace __detail
> >       +    {
> >       +      template<typename _Tp>
> >       +       concept __can_to_input = requires {
> to_input_view(std::declval<_Tp>()); };
> >       +    }
> >       +
> >       +    struct _ToInput : __adaptor::_RangeAdaptorClosure<_ToInput>
> >       +    {
> >       +      template<viewable_range _Range>
> >       +       requires __detail::__can_to_input<_Range>
> >       +       constexpr auto
> >       +       operator() [[nodiscard]] (_Range&& __r) const
> >       +       {
> >       +         if constexpr (input_range<_Range>
> >       +                       && !common_range<_Range>
> >       +                       && !forward_range<_Range>)
> >       +           return views::all(__r);
> >       +         else
> >       +           return to_input_view(std::forward<_Range>(__r));
> >       +       }
> >       +
> >       +      static constexpr bool _S_has_simple_call_op = true;
> >       +    };
> >       +
> >       +    inline constexpr _ToInput to_input;
> >       +  }
> >       +} // namespace ranges
> >       +#endif // __cpp_lib_ranges_to_input
> >       +
> >        _GLIBCXX_END_NAMESPACE_VERSION
> >        } // namespace std
> >        #endif // library concepts
> >       diff --git
> a/libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc
> b/libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc
> >       new file mode 100644
> >       index 00000000000..1e43281adb4
> >       --- /dev/null
> >       +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc
> >       @@ -0,0 +1,58 @@
> >       +// { dg-do run { target c++26 } }
> >       +
> >       +#include <ranges>
> >       +
> >       +#if __cpp_lib_ranges_to_input != 202502L
> >       +# error "Feature-test macro __cpp_lib_ranges_to_input has wrong
> value in <ranges>"
> >       +#endif
> >       +
> >       +#include <algorithm>
> >       +#include <vector>
> >       +#include <testsuite_hooks.h>
> >       +#include <testsuite_iterators.h>
> >       +
> >       +namespace ranges = std::ranges;
> >       +namespace views = std::views;
> >       +
> >       +void
> >       +test01()
> >       +{
> >       +  std::vector<int> r{1,2,3};
> >       +  auto v = r | views::to_input;
> >       +  using type = decltype(v);
> >       +  static_assert( ranges::input_range<type> &&
> !ranges::forward_range<type> );
> >       +
> >       +  VERIFY( ranges::equal(v.base(), r) );
> >       +  VERIFY( v.size() == r.size() );
> >       +  VERIFY( v.end() == r.end() );
> >       +  auto it = v.begin();
> >       +  VERIFY( it != r.end() );
> >       +  *it = 42;
> >       +  ++it;
> >       +  *it = 43;
> >       +  it++;
> >       +  ranges::iter_swap(v.begin(), it);
> >
> > As far as I can tell this is not invoking the iter_swap friend function,
> and instead defaulting to swap by 3 iter_moves.
> > We cannot copy the iterator, but you could replace v.begin(), with
> views::to_input(v).begin() to call the overload, and
> > have the same effect.
>
> v is the to_input_view, not the vector, so both arguments are
> to_input_view iterators and I'd expect the friend function gets
> used here?  Looks like it is, demonstrated by a static_assert(false)
> added to its body:
>
Indeed, I got confused by the name (v being for vector), and the friend
overload is called.
We are also calling begin on input_range twice, which is not guaranteed to
work in general,
but seem to be well-defined in this case.

>
> In file included from
> src/libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc:3:
> /scratchpad/gcc-build/x86_64-pc-linux-gnu/libstdc++-v3/include/ranges: In
> instantiation of ‘constexpr void std::ranges::iter_swap(const
> to_input_view<ref_view<std::__debug::vector<int> > >::_Iterator<true>&,
> const to_input_view<ref_view<std::__debug::vector<int> >
> >::_Iterator<true>&) requires
> indirectly_swappable<decltype(std::ranges::__access::__begin((declval<typename
> std::__conditional<_Const>::type<const _Vp, _Vp>&>)())),
> decltype(std::ranges::__access::__begin((declval<typename
> std::__conditional<_Const>::type<const _Vp, _Vp>&>)()))>’:
> /scratchpad/gcc-build/x86_64-pc-linux-gnu/libstdc++-v3/include/bits/iterator_concepts.h:949:15:
>  required from ‘constexpr void
> std::ranges::__iswap::_IterSwap::operator()(_Tp&&, _Up&&) const [with _Tp =
> std::ranges::to_input_view<std::ranges::ref_view<std::__debug::vector<int>
> > >::_Iterator<true>; _Up =
> std::ranges::to_input_view<std::ranges::ref_view<std::__debug::vector<int>
> > >::_Iterator<true>&]’
>   949 |             iter_swap(static_cast<_Tp&&>(__e1),
> static_cast<_Up&&>(__e2));
>       |
>  ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> src/libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc:34:20:
>  required from here
>    34 |   ranges::iter_swap(v.begin(), it);
>       |   ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
> /scratchpad/gcc-build/x86_64-pc-linux-gnu/libstdc++-v3/include/ranges:10529:21:
> error: static assertion failed
> 10529 |     { static_assert(false); ranges::iter_swap(__x._M_current,
> __y._M_current); }
>       |                     ^~~~~
> /scratchpad/gcc-build/x86_64-pc-linux-gnu/libstdc++-v3/include/ranges:10529:21:
> note: ‘false’ evaluates to false
>
> >       +  VERIFY( ranges::equal(r, (int[]){3,43,42}) );
> >       +  *it = ranges::iter_move(it);
> >       +  VERIFY( it == r.begin() + 2 );
> >       +  VERIFY( r.end() - it == 1 );
> >       +  VERIFY( it - r.end() == -1 );
> >       +}
> >       +
> >       +void
> >       +test02()
> >       +{
> >       +  int x[] = {1,2,3};
> >       +  __gnu_test::test_input_range<int> rx(x);
> >       +  static_assert( !ranges::common_range<decltype(rx)> );
> >       +  auto v = rx | views::to_input;
> >       +  using type = decltype(v);
> >       +  using type = ranges::ref_view<decltype(rx)>;
> >
> > I would prefer a more direct representation of this check, as
> static_assert(std::is_same_v<decltype(views::all(rx)), decltype())>);
>
> Sounds good.  The 'using' technique doesn't add much here since the type
> names are short and we don't subsequently use the alias anywhere.
>
> >       +}
> >       +
> >       +int
> >       +main()
> >       +{
> >       +  test01();
> >       +  test02();
> >       +}
> >       --
> >       2.49.0.rc1.37.ge969bc8759
> >
> >
> >

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