(CCing libstdc++@)
Could you resubmit this as a Git patch? See
https://gcc.gnu.org/contribute.html#patches
On Fri, 2 Jan 2026, Bingzhi wrote:
> Old code:
> # if _GLIBCXX_USE_BUILTIN_TRAIT(__is_scoped_enum)
> template<typename _Tp>
> struct is_scoped_enum
> : bool_constant<__is_scoped_enum(_Tp)>
> { };
> # else
> template<typename _Tp>
> struct is_scoped_enum
> : false_type
> { };
>
> template<typename _Tp>
> requires __is_enum(_Tp)
> && requires(remove_cv_t<_Tp> __t) { __t = __t; } // fails if incomplete
> struct is_scoped_enum<_Tp>
> : bool_constant<!requires(_Tp __t, void(*__f)(int)) { __f(__t); }>
> { };
> # endif
>
> New code:
> # if _GLIBCXX_USE_BUILTIN_TRAIT(__is_scoped_enum)
> template<typename _Tp>
> struct is_scoped_enum
> : bool_constant<__is_scoped_enum(_Tp)>
> { };
> # else
> template<typename _Tp>
> struct is_scoped_enum
> : false_type
> { };
>
> template<typename _Tp>
> requires __is_enum(_Tp)
> && requires { sizeof(_Tp); } // fails if incomplete
> struct is_scoped_enum<_Tp>
> : bool_constant<!requires(int __i) { __i = _Tp { }; }>
> { };
> # endif
>
> Easy to verify:
> struct S { operator int() { return 4; } };
> //enum E; // not legal.
> enum E {};
> enum Ei : int;
> enum class CE;
> enum U { Val = is_scoped_enum<U>::value };
> static_assert(not is_scoped_enum<int*>::value);
> static_assert(not is_scoped_enum<nullptr_t>::value);
> static_assert(not is_scoped_enum<S>::value);
> static_assert(not is_scoped_enum<E>::value);
> static_assert(not is_scoped_enum<Ei>::value);
> static_assert(is_scoped_enum<CE>::value);
> static_assert(not is_scoped_enum<U>::value);
>
>
