Re: [PATCH] libstdc++: Consistently use ::type when deriving from __and/or/not_

[Jonathan Wakely <jwakely@redhat.com>]

On Fri, 2 Sept 2022 at 17:39, Patrick Palka via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> Now that these internal type traits are again class templates, it's
> better to derive from the trait's ::type (which is either false_type or
> true_type) instead of from the trait itself, for sake of a shallower
> inheritance chain.  We usually do this but not always; this patch makes
> us consistently do so.
>
> Tested on x86_64-pc-lnux-gnu, does this look OK for trunk?  (Compile
> time for join.cc decreases by about 0.5% with this, avg of 10 runs.)

OK, thanks.


>
> libstdc++-v3/ChangeLog:
>
>         * include/std/tuple (tuple::_UseOtherCtor): Do ::type when
>         deriving from __and_, __or_ or __not_.
>         * include/std/type_traits (negation): Likewise.
>         (is_unsigned): Likewise.
>         (__is_implicitly_default_constructible): Likewise.
>         (is_trivially_destructible): Likewise.
>         (__is_nt_invocable_impl): Likewise.
> ---
>  libstdc++-v3/include/std/tuple       |  2 +-
>  libstdc++-v3/include/std/type_traits | 10 +++++-----
>  2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple
> index ddd7c226d80..26e248431ec 100644
> --- a/libstdc++-v3/include/std/tuple
> +++ b/libstdc++-v3/include/std/tuple
> @@ -826,7 +826,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>        // then TUPLE should match tuple(UTypes&&...) instead.
>        template<typename _Tuple, typename _Tp, typename _Up>
>         struct _UseOtherCtor<_Tuple, tuple<_Tp>, tuple<_Up>>
> -       : __or_<is_convertible<_Tuple, _Tp>, is_constructible<_Tp, _Tuple>>
> +       : __or_<is_convertible<_Tuple, _Tp>, is_constructible<_Tp, _Tuple>>::type
>         { };
>        // If TUPLE and *this each have a single element of the same type,
>        // then TUPLE should match a copy/move constructor instead.
> diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
> index be9f2955539..c0bb1cf64e3 100644
> --- a/libstdc++-v3/include/std/type_traits
> +++ b/libstdc++-v3/include/std/type_traits
> @@ -235,7 +235,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
>    template<typename _Pp>
>      struct negation
> -    : __not_<_Pp>
> +    : __not_<_Pp>::type
>      { };
>
>    /** @ingroup variable_templates
> @@ -845,7 +845,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>    /// is_unsigned
>    template<typename _Tp>
>      struct is_unsigned
> -    : public __and_<is_arithmetic<_Tp>, __not_<is_signed<_Tp>>>
> +    : public __and_<is_arithmetic<_Tp>, __not_<is_signed<_Tp>>>::type
>      { };
>
>    /// @cond undocumented
> @@ -1222,7 +1222,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>    template <typename _Tp>
>      struct __is_implicitly_default_constructible
>      : public __and_<__is_constructible_impl<_Tp>,
> -                   __is_implicitly_default_constructible_safe<_Tp>>
> +                   __is_implicitly_default_constructible_safe<_Tp>>::type
>      { };
>
>    /// is_trivially_copy_constructible
> @@ -1282,7 +1282,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>    template<typename _Tp>
>      struct is_trivially_destructible
>      : public __and_<__is_destructible_safe<_Tp>,
> -                   __bool_constant<__has_trivial_destructor(_Tp)>>
> +                   __bool_constant<__has_trivial_destructor(_Tp)>>::type
>      {
>        static_assert(std::__is_complete_or_unbounded(__type_identity<_Tp>{}),
>         "template argument must be a complete class or an unbounded array");
> @@ -2975,7 +2975,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>      struct __is_nt_invocable_impl<_Result, _Ret,
>                                   __void_t<typename _Result::type>>
>      : __or_<is_void<_Ret>,
> -           __is_nothrow_convertible<typename _Result::type, _Ret>>
> +           __is_nothrow_convertible<typename _Result::type, _Ret>>::type
>      { };
>    /// @endcond
>
> --
> 2.37.2.490.g6c8e4ee870
>