On Thu, Nov 12, 2026 at 11:39 AM Jonathan Wakely <[email protected]> wrote:
> This helper macro is defined in <type_traits> but only used in a test.
>
> The uses of it in our headers were removed in these commits:
> r5-4826-g847e9cf81e5101 Define __void_t and SFINAE-friendly
> iterator_traits.
> r6-1925-g4f44c5556fc384 ptr_traits.h (__ptrtr_elt_type, [...]): Remove
> r7-3818-g57c4fbc64b6c15 Simplify reference_wrapper nested typedefs
>
> So we've kept it around unnecessarily for a decade. Remove it from the
> public header and update the test to not require it.
>
> libstdc++-v3/ChangeLog:
>
> * include/std/type_traits (_GLIBCXX_HAS_NESTED_TYPE): Remove
> macro.
> * testsuite/20_util/reference_wrapper/typedefs-3.cc: Define
> test traits without using _GLIBCXX_HAS_NESTED_TYPE.
> ---
>
> Tested 20_util/* and running the other tests now on x86_64-linux.
>
LGTM
>
> libstdc++-v3/include/std/type_traits | 14 ---------
> .../20_util/reference_wrapper/typedefs-3.cc | 29 ++++++++++++-------
> 2 files changed, 19 insertions(+), 24 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/type_traits
> b/libstdc++-v3/include/std/type_traits
> index 83dbad17ade9..d4199dd5a33b 100644
> --- a/libstdc++-v3/include/std/type_traits
> +++ b/libstdc++-v3/include/std/type_traits
> @@ -3045,20 +3045,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> using __detected_or_t
> = typename __detected_or<_Default, _Op, _Args...>::type;
>
> - /**
> - * Use SFINAE to determine if the type _Tp has a publicly-accessible
> - * member type _NTYPE.
> - */
> -#define _GLIBCXX_HAS_NESTED_TYPE(_NTYPE) \
> - template<typename _Tp, typename = __void_t<>>
> \
> - struct __has_##_NTYPE \
> - : false_type \
> - { }; \
> - template<typename _Tp> \
> - struct __has_##_NTYPE<_Tp, __void_t<typename _Tp::_NTYPE>> \
> - : true_type
> \
> - { };
> -
> template <typename _Tp>
> struct __is_swappable;
>
> diff --git
> a/libstdc++-v3/testsuite/20_util/reference_wrapper/typedefs-3.cc
> b/libstdc++-v3/testsuite/20_util/reference_wrapper/typedefs-3.cc
> index 2b2b36108c6d..9c7899e32085 100644
> --- a/libstdc++-v3/testsuite/20_util/reference_wrapper/typedefs-3.cc
> +++ b/libstdc++-v3/testsuite/20_util/reference_wrapper/typedefs-3.cc
> @@ -44,24 +44,33 @@ struct S12 : S1, S2 { };
>
> struct S012 : S0, S1, S2 { };
>
> -using std::true_type;
> -using std::false_type;
> -using std::__void_t;
> -
> -_GLIBCXX_HAS_NESTED_TYPE(argument_type)
> -_GLIBCXX_HAS_NESTED_TYPE(first_argument_type)
> -_GLIBCXX_HAS_NESTED_TYPE(second_argument_type)
> +template<typename> using void_t = void;
>
> +template<typename T, typename = void>
> + struct has_arg_type
> + : std::false_type
> + { };
> template<typename T>
> - struct has_arg_type : __has_argument_type<T>
> + struct has_arg_type<T, void_t<typename T::argument_type>>
> + : std::true_type
> { };
>
> +template<typename T, typename = void>
> + struct has_1st_arg_type
> + : std::false_type
> + { };
> template<typename T>
> - struct has_1st_arg_type : __has_first_argument_type<T>
> + struct has_1st_arg_type<T, void_t<typename T::first_argument_type>>
> + : std::true_type
> { };
>
> +template<typename T, typename = void>
> + struct has_2nd_arg_type
> + : std::false_type
> + { };
> template<typename T>
> - struct has_2nd_arg_type : __has_second_argument_type<T>
> + struct has_2nd_arg_type<T, void_t<typename T::second_argument_type>>
> + : std::true_type
> { };
>
> template<typename T, bool = has_arg_type<T>::value>
> --
> 2.56.0
>
>
