Re: [PATCH v2 2/2] libstdc++: use new built-in trait __is_scalar for std::is_scalar

[Jonathan Wakely <jwakely@redhat.com>]

On Sat, 8 Jul 2023 at 05:47, Ken Matsui via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> This patch gets std::is_scalar to dispatch to new built-in trait
> __is_scalar.
>
> libstdc++-v3/ChangeLog:
>
>         * include/std/type_traits (is_scalar): Use __is_scalar built-in
>         trait.
>         (is_scalar_v): Likewise.

OK for trunk (conditional on the front-end change being committed
first of course).


>
> Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
> ---
>  libstdc++-v3/include/std/type_traits | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
> index 0e7a9c9c7f3..bc90b2c61ca 100644
> --- a/libstdc++-v3/include/std/type_traits
> +++ b/libstdc++-v3/include/std/type_traits
> @@ -678,11 +678,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>      struct is_member_pointer;
>
>    /// is_scalar
> +#if __has_builtin(__is_scalar)
> +  template<typename _Tp>
> +    struct is_scalar
> +    : public __bool_constant<__is_scalar(_Tp)>
> +    { };
> +#else
>    template<typename _Tp>
>      struct is_scalar
>      : public __or_<is_arithmetic<_Tp>, is_enum<_Tp>, is_pointer<_Tp>,
>                     is_member_pointer<_Tp>, is_null_pointer<_Tp>>::type
>      { };
> +#endif
>
>    /// is_compound
>    template<typename _Tp>
> @@ -3204,8 +3211,15 @@ template <typename _Tp>
>    inline constexpr bool is_fundamental_v = is_fundamental<_Tp>::value;
>  template <typename _Tp>
>    inline constexpr bool is_object_v = is_object<_Tp>::value;
> +
> +#if __has_builtin(__is_scalar)
> +template <typename _Tp>
> +  inline constexpr bool is_scalar_v = __is_scalar(_Tp);
> +#else
>  template <typename _Tp>
>    inline constexpr bool is_scalar_v = is_scalar<_Tp>::value;
> +#endif
> +
>  template <typename _Tp>
>    inline constexpr bool is_compound_v = is_compound<_Tp>::value;
>  template <typename _Tp>
> --
> 2.41.0
>