On Sat, Mar 20, 2021 at 3:58 AM Jonathan Wakely <jwakely....@gmail.com> wrote: > > > > On Sat, 20 Mar 2021, 01:13 Tim Song via Libstdc++, <libstd...@gcc.gnu.org> > wrote: >> >> On Fri, Mar 19, 2021 at 3:13 PM Jonathan Wakely via Libstdc++ >> <libstd...@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. > >
Using int avoids the hard error, but it appears to give the wrong answer (presumably because the is_convertible check fails due to E being incomplete). This may need to be handled explicitly?
