On Wed, 11 Jun 2025 at 10:24, Tomasz Kaminski <tkami...@redhat.com> wrote:
>
>
>
> On Tue, Jun 10, 2025 at 12:37 PM Jonathan Wakely <jwak...@redhat.com> wrote:
>>
>> By using std::is_trivially_destructible instead of the old
>> __has_trivial_destructor built-in we no longer need the static_assert to
>> deal with types with deleted destructors. All non-destructible types,
>> including those with deleted destructors, will now give user-friendly
>> diagnostics that clearly explain the problem.
>>
>> Also combine the _Destroy_aux and _Destroy_n_aux class templates used
>> for C++98 into one, so that we perform fewer expensive class template
>> instantiations.
>>
>> libstdc++-v3/ChangeLog:
>>
>> PR libstdc++/120390
>> * include/bits/stl_construct.h (_Destroy_aux::__destroy_n): New
>> static member function.
>> (_Destroy_aux<true>::__destroy_n): Likewise.
>> (_Destroy_n_aux): Remove.
>> (_Destroy(ForwardIterator, ForwardIterator)): Remove
>> static_assert. Use is_trivially_destructible instead of
>> __has_trivial_destructor.
>> (_Destroy_n): Likewise. Use _Destroy_aux::__destroy_n instead of
>> _Destroy_n_aux::__destroy_n.
>> *
>> testsuite/20_util/specialized_algorithms/memory_management_tools/destroy_neg.cc:
>> Adjust dg-error strings. Move destroy_n tests to ...
>> *
>> testsuite/20_util/specialized_algorithms/memory_management_tools/destroy_n_neg.cc:
>> New test.
>> * testsuite/23_containers/vector/cons/destructible_debug_neg.cc:
>> Adjust dg-error strings.
>> * testsuite/23_containers/vector/cons/destructible_neg.cc:
>> Likewise.
>> ---
>>
>> Tested x86_64-linux.
>
> LGTM.
> Not directly related to the patch, but I have noticed that for c++98, for
> trivially destructible
> types we make sure that we traverse range (we call advance) however in C++11+
> mode
> we do not do that. Something changed in standard?
I think they should be equivalent. For C++98 the
_Destroy_aux<true>::__destroy_n function calls advance and returns the
result:
>> @@ -189,6 +198,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> template<typename _ForwardIterator>
>> static void
>> __destroy(_ForwardIterator, _ForwardIterator) { }
>> +
>> + template<typename _ForwardIterator, typename _Size>
>> + static _ForwardIterator
>> + __destroy_n(_ForwardIterator __first, _Size __count)
>> + {
>> + std::advance(__first, __count);
>> + return __first;
>> + }
>> };
>> #endif
For C++11 we do the same directly in the _Destroy_n function:
>> @@ -260,10 +247,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> typedef typename iterator_traits<_ForwardIterator>::value_type
>> _Value_type;
>> #if __cplusplus >= 201103L
>> - // A deleted destructor is trivial, this ensures we reject such types:
>> - static_assert(is_destructible<_Value_type>::value,
>> - "value type is destructible");
>> - if constexpr (!__has_trivial_destructor(_Value_type))
>> + if constexpr (!is_trivially_destructible<_Value_type>::value)
>> for (; __count > 0; (void)++__first, --__count)
>> std::_Destroy(std::__addressof(*__first));
>> #if __cpp_constexpr_dynamic_alloc // >= C++20
>> @@ -275,7 +259,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> std::advance(__first, __count);
>> return __first;
^ here.
