On Thu, 13 Jul 2023 at 03:41, Ken Matsui via Libstdc++ <
libstdc++@gcc.gnu.org> wrote:

> This patch gets std::is_function to dispatch to new built-in trait
> __is_function.
>
> libstdc++-v3/ChangeLog:
>
>         * include/std/type_traits (is_function): Use __is_function built-in
>         trait.
>         (is_function_v): Likewise. Optimize its implementation.
>
> Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
>

OK for trunk (after the compiler change is approved).




> ---
>  libstdc++-v3/include/std/type_traits | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/libstdc++-v3/include/std/type_traits
> b/libstdc++-v3/include/std/type_traits
> index 2a14df7e5f9..7ef50a2e64f 100644
> --- a/libstdc++-v3/include/std/type_traits
> +++ b/libstdc++-v3/include/std/type_traits
> @@ -594,6 +594,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>      { };
>
>    /// is_function
> +#if __has_builtin(__is_function)
> +  template<typename _Tp>
> +    struct is_function
> +    : public __bool_constant<__is_function(_Tp)>
> +    { };
> +#else
>    template<typename _Tp>
>      struct is_function
>      : public __bool_constant<!is_const<const _Tp>::value> { };
> @@ -605,6 +611,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>    template<typename _Tp>
>      struct is_function<_Tp&&>
>      : public false_type { };
> +#endif
>
>  #define __cpp_lib_is_null_pointer 201309L
>
> @@ -3197,8 +3204,18 @@ template <typename _Tp>
>    inline constexpr bool is_union_v = __is_union(_Tp);
>  template <typename _Tp>
>    inline constexpr bool is_class_v = __is_class(_Tp);
> +
> +#if __has_builtin(__is_function)
>  template <typename _Tp>
> -  inline constexpr bool is_function_v = is_function<_Tp>::value;
> +  inline constexpr bool is_function_v = __is_function(_Tp);
> +#else
> +template <typename _Tp>
> +  inline constexpr bool is_function_v = !is_const_v<const _Tp>;
> +template <typename _Tp>
> +  inline constexpr bool is_function_v<_Tp&> = false;
> +template <typename _Tp>
> +  inline constexpr bool is_function_v<_Tp&&> = false;
> +#endif
>
>  #if __has_builtin(__is_reference)
>  template <typename _Tp>
> --
> 2.41.0
>
>