Re: [committed] libstdc++: Add std::is_scoped_enum for C++23

[Jonathan Wakely <jwakely.gcc@gmail.com>]

On Sat, 20 Mar 2021, 01:13 Tim Song via Libstdc++, <libstdc++@gcc.gnu.org>
wrote:

> On Fri, Mar 19, 2021 at 3:13 PM Jonathan Wakely via Libstdc++
> <libstdc++@gcc.gnu.org> wrote:
> >
> > Implement this C++23 feature, as proposed by P1048R1.
> >
> > This implementation assumes that a C++23 compiler supports concepts
> > already. I don't see any point in using preprocessor hacks to detect
> > compilers which define __cplusplus to a post-C++20 value but don't
> > support concepts yet.
> >
> > libstdc++-v3/ChangeLog:
> >
> >         * include/std/type_traits (is_scoped_enum): Define.
> >         * include/std/version (__cpp_lib_is_scoped_enum): Define.
> >         * testsuite/20_util/is_scoped_enum/value.cc: New test.
> >         * testsuite/20_util/is_scoped_enum/version.cc: New test.
> >
> > Tested powerpc64le-linux. Committed to trunk.
> >
>
> Using __underlying_type breaks for incomplete enumeration types. GCC
> doesn't have incomplete scoped enums due to
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89025 but unscoped ones
> exist:
>
> enum E {
>     x = std::is_scoped_enum_v<E>
> };
>

Thanks, I'll just use int then. Maybe not until Monday though.