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From: Jonathan Wakely <jwakely.gcc@gmail.com>
Date: Sun, 3 Oct 2021 10:07:13 +0100
Message-ID: <CAH6eHdQHHXCr9xb9bgC4EwOpz47+2HG6z2+LyT-DH1Yw-DU=zg@mail.gmail.com>
Subject: Re: [committed] libstdc++: Allow visiting inherited variants [PR
 90943]
To: =?UTF-8?Q?Daniel_Kr=C3=BCgler?= <daniel.kruegler@gmail.com>
Cc: Jonathan Wakely <jwakely@redhat.com>, "libstdc++" <libstdc++@gcc.gnu.org>, 
 gcc-patches List <gcc-patches@gcc.gnu.org>
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On Sat, 2 Oct 2021, 13:50 Daniel Kr=C3=BCgler via Libstdc++, <
libstdc++@gcc.gnu.org> wrote:

> Am Fr., 1. Okt. 2021 um 21:57 Uhr schrieb Jonathan Wakely via
> Libstdc++ <libstdc++@gcc.gnu.org>:
> >
> > Implement the changes from P2162R2 (as a DR for C++17).
> >
> > Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
> >
> > libstdc++-v3/ChangeLog:
> >
> >         PR libstdc++/90943
> >         * include/std/variant (__cpp_lib_variant): Update value.
> >         (__detail::__variant::__as): New helpers implementing the
> >         as-variant exposition-only function templates.
> >         (visit, visit<R>): Use __as to upcast the variant parameters.
> >         * include/std/version (__cpp_lib_variant): Update value.
> >         * testsuite/20_util/variant/visit_inherited.cc: New test.
> >
> > Tested powerpc64le-linux. Committed to trunk.
> >
>
> I'm wondering why the first __as overload is not noexcept as well (or
> asking it the other way around: Why different exception-specifications
> are used for the different overloads):
>
> +  // The __as function templates implement the exposition-only
> "as-variant"
> +
> +  template<typename... _Types>
> +    constexpr std::variant<_Types...>&
> +    __as(std::variant<_Types...>& __v)
> +    { return __v; }
>

Probably just an oversight, I'll check again and fix it. Thanks!