Re: [PATCH] libstdc++: Implement ranges::as_rvalue_view from P2446R2

[Jonathan Wakely <jwakely@redhat.com>]

On Mon, 31 Oct 2022 at 20:33, Patrick Palka via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?

OK, thanks.

We should update https://gcc.gnu.org/gcc-13/changes.html#libstdcxx again soon.

>
> libstdc++-v3/ChangeLog:
>
>         * include/std/ranges (as_rvalue_view): Define.
>         (enable_borrowed_range<as_rvalue_view>): Define.
>         (views::__detail::__can_as_rvalue_view): Define.
>         (views::_AsRvalue, views::as_rvalue): Define.
>         * testsuite/std/ranges/adaptors/as_rvalue/1.cc: New test.
> ---
>  libstdc++-v3/include/std/ranges               | 88 +++++++++++++++++++
>  .../std/ranges/adaptors/as_rvalue/1.cc        | 47 ++++++++++
>  2 files changed, 135 insertions(+)
>  create mode 100644 libstdc++-v3/testsuite/std/ranges/adaptors/as_rvalue/1.cc
>
> diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
> index 959886a1a55..239b3b61d30 100644
> --- a/libstdc++-v3/include/std/ranges
> +++ b/libstdc++-v3/include/std/ranges
> @@ -8486,6 +8486,94 @@ namespace views::__adaptor
>
>      inline constexpr _CartesianProduct cartesian_product;
>    }
> +
> +  template<input_range _Vp>
> +    requires view<_Vp>
> +  class as_rvalue_view : public view_interface<as_rvalue_view<_Vp>>
> +  {
> +    _Vp _M_base = _Vp();
> +
> +  public:
> +    as_rvalue_view() requires default_initializable<_Vp> = default;
> +
> +    constexpr explicit
> +    as_rvalue_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 move_iterator(ranges::begin(_M_base)); }
> +
> +    constexpr auto
> +    begin() const requires range<const _Vp>
> +    { return move_iterator(ranges::begin(_M_base)); }
> +
> +    constexpr auto
> +    end() requires (!__detail::__simple_view<_Vp>)
> +    {
> +      if constexpr (common_range<_Vp>)
> +       return move_iterator(ranges::end(_M_base));
> +      else
> +       return move_sentinel(ranges::end(_M_base));
> +    }
> +
> +    constexpr auto
> +    end() const requires range<const _Vp>
> +    {
> +      if constexpr (common_range<const _Vp>)
> +       return move_iterator(ranges::end(_M_base));
> +      else
> +       return move_sentinel(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>
> +    as_rvalue_view(_Range&&) -> as_rvalue_view<views::all_t<_Range>>;
> +
> +  template<typename _Tp>
> +    inline constexpr bool enable_borrowed_range<as_rvalue_view<_Tp>>
> +      = enable_borrowed_range<_Tp>;
> +
> +  namespace views
> +  {
> +    namespace __detail
> +    {
> +      template<typename _Tp>
> +       concept __can_as_rvalue_view = requires { as_rvalue_view(std::declval<_Tp>()); };
> +    }
> +
> +    struct _AsRvalue : __adaptor::_RangeAdaptorClosure
> +    {
> +      template<viewable_range _Range>
> +       requires __detail::__can_as_rvalue_view<_Range>
> +       constexpr auto
> +       operator() [[nodiscard]] (_Range&& __r) const
> +       {
> +         if constexpr (same_as<range_rvalue_reference_t<_Range>,
> +                               range_reference_t<_Range>>)
> +           return views::all(std::forward<_Range>(__r));
> +         else
> +           return as_rvalue_view(std::forward<_Range>(__r));
> +       }
> +    };
> +
> +    inline constexpr _AsRvalue as_rvalue;
> +  }
>  #endif // C++23
>  } // namespace ranges
>
> diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/as_rvalue/1.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/as_rvalue/1.cc
> new file mode 100644
> index 00000000000..8ca4f50e9d2
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/as_rvalue/1.cc
> @@ -0,0 +1,47 @@
> +// { dg-options "-std=gnu++23" }
> +// { dg-do run { target c++23 } }
> +
> +#include <ranges>
> +#include <algorithm>
> +#include <memory>
> +#include <testsuite_hooks.h>
> +#include <testsuite_iterators.h>
> +
> +namespace ranges = std::ranges;
> +namespace views = std::views;
> +
> +constexpr bool
> +test01()
> +{
> +
> +  std::unique_ptr<int> a[3] = { std::make_unique<int>(1),
> +                               std::make_unique<int>(2),
> +                               std::make_unique<int>(3) };
> +  std::unique_ptr<int> b[3];
> +  auto v = a | views::as_rvalue;
> +  ranges::copy(v, b);
> +  VERIFY( ranges::all_of(a, [](auto& p) { return p.get() == nullptr; }) );
> +  VERIFY( ranges::equal(b | views::transform([](auto& p) { return *p; }), (int[]){1, 2, 3}) );
> +
> +  return true;
> +}
> +
> +void
> +test02()
> +{
> +  std::unique_ptr<int> x = std::make_unique<int>(42);
> +  std::unique_ptr<int> y;
> +  __gnu_test::test_input_range rx(&x, &x+1);
> +  auto v = rx | views::as_rvalue;
> +  static_assert(!ranges::common_range<decltype(v)>);
> +  ranges::copy(v, &y);
> +  VERIFY( x.get() == nullptr );
> +  VERIFY( *y == 42 );
> +}
> +
> +int
> +main()
> +{
> +  static_assert(test01());
> +  test02();
> +}
> --
> 2.38.1.381.gc03801e19c
>