On Tue, May 5, 2026 at 5:04 PM Jonathan Wakely <[email protected]> wrote:
> Clang 10 added support for concepts, so we no longer need to support
> C++20 compilers that don't define __cpp_concepts.
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/shared_ptr.h (_UnboundedArray, _BoundedArray)
> (_NotUnboundedArray): Remove fallback definition for C++20
> compilers that don't define __cpp_concepts.
> * include/bits/shared_ptr_base.h (_Sp_counted_ptr_inplace):
> Remove fallback declaration of _Sp_overwrite_tag partial
> specialization.
> ---
>
> Tested x86_64-linux.
>
> libstdc++-v3/include/bits/shared_ptr.h | 18 ------------------
> libstdc++-v3/include/bits/shared_ptr_base.h | 5 -----
> 2 files changed, 23 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/shared_ptr.h
> b/libstdc++-v3/include/bits/shared_ptr.h
> index fd00384df223..ada32d3d3cb9 100644
> --- a/libstdc++-v3/include/bits/shared_ptr.h
> +++ b/libstdc++-v3/include/bits/shared_ptr.h
> @@ -114,38 +114,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
> #if __glibcxx_shared_ptr_arrays >= 201707L
> // Constraint for overloads taking array types with unknown bound, U[].
> -#if __cpp_concepts
> template<typename _Tp>
> requires is_array_v<_Tp> && (extent_v<_Tp> == 0)
> using _UnboundedArray = _Tp;
>
Could we replace this constrained alias with requires/concept on the
function?
that are using it? This version was always deductible, so shouldn't make
difference.
May however change mangling.
> -#else
> - template<typename _Tp>
> - using _UnboundedArray
> - = __enable_if_t<__is_array_unknown_bounds<_Tp>::value, _Tp>;
> -#endif
>
> // Constraint for overloads taking array types with known bound, U[N].
> -#if __cpp_concepts
> template<typename _Tp>
> requires (extent_v<_Tp> != 0)
> using _BoundedArray = _Tp;
> -#else
> - template<typename _Tp>
> - using _BoundedArray
> - = __enable_if_t<__is_array_known_bounds<_Tp>::value, _Tp>;
> -#endif
>
> #if __glibcxx_smart_ptr_for_overwrite
> // Constraint for overloads taking either non-array or bounded array,
> U[N].
> -#if __cpp_concepts
> template<typename _Tp>
> requires (!is_array_v<_Tp>) || (extent_v<_Tp> != 0)
> using _NotUnboundedArray = _Tp;
> -#else
> - template<typename _Tp>
> - using _NotUnboundedArray
> - = __enable_if_t<!__is_array_unknown_bounds<_Tp>::value, _Tp>;
> -#endif
> #endif // smart_ptr_for_overwrite
> #endif // shared_ptr_arrays
>
> diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h
> b/libstdc++-v3/include/bits/shared_ptr_base.h
> index cf1be953af2c..a64131bb9e12 100644
> --- a/libstdc++-v3/include/bits/shared_ptr_base.h
> +++ b/libstdc++-v3/include/bits/shared_ptr_base.h
> @@ -696,14 +696,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> // Partial specialization used for
> make_shared_for_overwrite<non-array>().
> // This partial specialization is used when the allocator's value type
> // is the special _Sp_overwrite_tag type.
> -#if __cpp_concepts
> template<typename _Tp, typename _Alloc, _Lock_policy _Lp>
> requires is_same_v<typename _Alloc::value_type, _Sp_overwrite_tag>
> class _Sp_counted_ptr_inplace<_Tp, _Alloc, _Lp> final
> -#else
> - template<typename _Tp, template<typename> class _Alloc, _Lock_policy
> _Lp>
> - class _Sp_counted_ptr_inplace<_Tp, _Alloc<_Sp_overwrite_tag>, _Lp>
> final
> -#endif
> : public _Sp_counted_base<_Lp>
> {
> [[no_unique_address]] _Alloc _M_alloc;
> --
> 2.54.0
>
>
