Re: [PATCH] libstdc++: Implement LWG 3715 changes to view_interface::empty

[Jonathan Wakely <jwakely@redhat.com>]

On Wed, 8 Mar 2023 at 15:53, Patrick Palka via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?

OK. I think this would make sense for 12 too.

>
> libstdc++-v3/ChangeLog:
>
>         * include/bits/ranges_util.h (view_interface::empty): Add
>         preferred overloads that use ranges::size when the range is
>         sized as per LWG 3715.
>         * testsuite/std/ranges/adaptors/lwg3715.cc: New test.
> ---
>  libstdc++-v3/include/bits/ranges_util.h       | 16 +++++++--
>  .../testsuite/std/ranges/adaptors/lwg3715.cc  | 33 +++++++++++++++++++
>  2 files changed, 47 insertions(+), 2 deletions(-)
>  create mode 100644 libstdc++-v3/testsuite/std/ranges/adaptors/lwg3715.cc
>
> diff --git a/libstdc++-v3/include/bits/ranges_util.h b/libstdc++-v3/include/bits/ranges_util.h
> index e4643e31a20..880a0ce0143 100644
> --- a/libstdc++-v3/include/bits/ranges_util.h
> +++ b/libstdc++-v3/include/bits/ranges_util.h
> @@ -97,15 +97,27 @@ namespace ranges
>        constexpr bool
>        empty()
>        noexcept(noexcept(_S_empty(_M_derived())))
> -      requires forward_range<_Derived>
> +      requires forward_range<_Derived> && (!sized_range<_Derived>)
>        { return _S_empty(_M_derived()); }
>
> +      constexpr bool
> +      empty()
> +      noexcept(noexcept(ranges::size(_M_derived()) == 0))
> +      requires sized_range<_Derived>
> +      { return ranges::size(_M_derived()) == 0; }
> +
>        constexpr bool
>        empty() const
>        noexcept(noexcept(_S_empty(_M_derived())))
> -      requires forward_range<const _Derived>
> +      requires forward_range<const _Derived> && (!sized_range<const _Derived>)
>        { return _S_empty(_M_derived()); }
>
> +      constexpr bool
> +      empty() const
> +      noexcept(noexcept(ranges::size(_M_derived()) == 0))
> +      requires sized_range<const _Derived>
> +      { return ranges::size(_M_derived()) == 0; }
> +
>        constexpr explicit
>        operator bool() noexcept(noexcept(ranges::empty(_M_derived())))
>        requires requires { ranges::empty(_M_derived()); }
> diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/lwg3715.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/lwg3715.cc
> new file mode 100644
> index 00000000000..96ee7087be0
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/lwg3715.cc
> @@ -0,0 +1,33 @@
> +// { dg-options "-std=gnu++23" }
> +// { dg-do run { target c++23 } }
> +
> +// Verify LWG 3715 changes.
> +
> +#include <ranges>
> +#include <sstream>
> +#include <testsuite_hooks.h>
> +
> +void
> +test01()
> +{
> +  std::istringstream ints("0 1 2 3 4");
> +  auto i = std::views::istream<int>(ints);
> +  auto r4 = std::views::counted(i.begin(), 4) | std::views::chunk(2);
> +  VERIFY( !r4.empty() );
> +}
> +
> +void
> +test02()
> +{
> +  std::istringstream ints("0 1 2 3 4");
> +  auto i = std::views::istream<int>(ints);
> +  auto r0 = std::views::counted(i.begin(), 0) | std::views::chunk(2);
> +  VERIFY( r0.empty() );
> +}
> +
> +int
> +main()
> +{
> +  test01();
> +  test02();
> +}
> --
> 2.40.0.rc0.57.g454dfcbddf
>