On Tue, 24 Oct 2023 at 03:16, Ken Matsui <kmat...@gcc.gnu.org> wrote:
> This patch optimizes the compilation performance of std::is_function > by dispatching to the new __is_function built-in trait. > > libstdc++-v3/ChangeLog: > > * include/std/type_traits (is_function): Use __is_function > built-in trait. > (is_function_v): Likewise. Optimize its implementation. > (is_const_v): Move on top of is_function_v as is_function_v now > depends on is_const_v. > I think I'd prefer to keep is_const_v where it is now, adjacent to is_volatile_v, and move is_function_v after those. i.e. like this (but with the additional changes to use the new built-in): --- a/libstdc++-v3/include/std/type_traits +++ b/libstdc++-v3/include/std/type_traits @@ -3198,8 +3198,8 @@ template <typename _Tp> inline constexpr bool is_union_v = __is_union(_Tp); template <typename _Tp> inline constexpr bool is_class_v = __is_class(_Tp); -template <typename _Tp> - inline constexpr bool is_function_v = is_function<_Tp>::value; +// is_function_v is defined below, after is_const_v. + template <typename _Tp> inline constexpr bool is_reference_v = false; template <typename _Tp> @@ -3226,6 +3226,8 @@ template <typename _Tp> inline constexpr bool is_volatile_v = false; template <typename _Tp> inline constexpr bool is_volatile_v<volatile _Tp> = true; +template <typename _Tp> + inline constexpr bool is_function_v = is_function<_Tp>::value; template <typename _Tp> inline constexpr bool is_trivial_v = __is_trivial(_Tp); The variable templates are currently defined in the order shown in the standard, in te [meta.type.synop] synopsis, and in the [meta.unary.cat] table. So let's move _is_function_v later and add a comment saying why it's not in the expected place.
