`ureact::merge` can't compile in latest MSVC in c++20 mode about ureact

[YarikTH]

Log from CI

Run cmake --build . --parallel 10 --config Release
  cmake --build . --parallel 10 --config Release
  shell: C:\Program Files\PowerShell\7\pwsh.EXE -command ". '{0}'"
MSBuild version 17.7.2+d6990bcfa for .NET Framework

// ============================================================================================================================================================
// ============================================================================================================================================================
// ============================================================================================================================================================

D:\a\ureact\ureact\include\ureact/adaptor/merge.hpp(41,62): error C2039: 'copy_events_from': is not a member of 'ureact::v0::detail::event_merge_node<E,Source,E>::update::<lambda_1>' [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=int,
              E=std::string
          ]
D:\a\ureact\ureact\include\ureact/adaptor/merge.hpp(41,98): message : see declaration of 'ureact::v0::detail::event_merge_node<E,Source,E>::update::<lambda_1>' [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=int,
              E=std::string
          ]
D:\a\ureact\ureact\include\ureact/adaptor/merge.hpp(37,45): message : while compiling class template member function 'ureact::v0::detail::update_result ureact::v0::detail::event_merge_node<E,Source,E>::update(void)' [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=int,
              E=std::string
          ]
D:\a\ureact\ureact\include\ureact/detail/node_base.hpp(29): message : see reference to class template instantiation 'ureact::v0::detail::event_merge_node<E,Source,E>' being compiled [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=int,
              E=std::string
          ]
D:\a\ureact\ureact\include\ureact/detail/node_base.hpp(40,17): message : see reference to function template instantiation 'std::shared_ptr<ureact::v0::detail::event_merge_node<E,Source,E>> ureact::v0::detail::create_node<ureact::v0::detail::event_merge_node<E,Source,E>,const ureact::v0::context&,const ureact::v0::events<int>&,const ureact::v0::events<E>&>(const ureact::v0::context &,const ureact::v0::events<int> &,const ureact::v0::events<E> &)' being compiled [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=int,
              E=std::string
          ]
D:\a\ureact\ureact\include\ureact/adaptor/merge.hpp(88,24): message : see reference to function template instantiation 'Ret ureact::v0::detail::create_wrapped_node<ureact::v0::events<E>,ureact::v0::detail::event_merge_node<E,Source,E>,const ureact::v0::context&,const ureact::v0::events<int>&,const ureact::v0::events<E>&>(const ureact::v0::context &,const ureact::v0::events<int> &,const ureact::v0::events<E> &)' being compiled [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Ret=ureact::v0::events<E>,
              Source=int,
              E=std::string
          ]
D:\a\ureact\ureact\tests\src\adaptor\merge.cpp(80,34): message : see reference to function template instantiation 'Ret ureact::v0::detail::MergeAdaptor<merged_type>::operator ()<E,std::basic_string<char,std::char_traits<char>,std::allocator<char>>>(const ureact::v0::events<E> &,const ureact::v0::events<std::basic_string<char,std::char_traits<char>,std::allocator<char>>> &) const' being compiled [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Ret=ureact::v0::events<E>,
              E=int
          ]

// ============================================================================================================================================================
// ============================================================================================================================================================
// ============================================================================================================================================================

D:\a\ureact\ureact\include\ureact/adaptor/merge.hpp(41,62): error C2039: 'copy_events_from': is not a member of 'ureact::v0::detail::event_merge_node<E,Source,E>::update::<lambda_1>' [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=int,
              E=int
          ]
D:\a\ureact\ureact\include\ureact/adaptor/merge.hpp(41,98): message : see declaration of 'ureact::v0::detail::event_merge_node<E,Source,E>::update::<lambda_1>' [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=int,
              E=int
          ]
D:\a\ureact\ureact\include\ureact/adaptor/merge.hpp(37,45): message : while compiling class template member function 'ureact::v0::detail::update_result ureact::v0::detail::event_merge_node<E,Source,E>::update(void)' [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=int,
              E=int
          ]
D:\a\ureact\ureact\include\ureact/detail/node_base.hpp(29): message : see reference to class template instantiation 'ureact::v0::detail::event_merge_node<E,Source,E>' being compiled [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=int,
              E=int
          ]
D:\a\ureact\ureact\include\ureact/detail/node_base.hpp(40,17): message : see reference to function template instantiation 'std::shared_ptr<ureact::v0::detail::event_merge_node<E,Source,E>> ureact::v0::detail::create_node<ureact::v0::detail::event_merge_node<E,Source,E>,const ureact::v0::context&,const ureact::v0::events<E>&,const ureact::v0::events<E>&>(const ureact::v0::context &,const ureact::v0::events<E> &,const ureact::v0::events<E> &)' being compiled [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=int,
              E=int
          ]
D:\a\ureact\ureact\include\ureact/adaptor/merge.hpp(88,24): message : see reference to function template instantiation 'Ret ureact::v0::detail::create_wrapped_node<ureact::v0::events<E>,ureact::v0::detail::event_merge_node<E,Source,E>,const ureact::v0::context&,const ureact::v0::events<E>&,const ureact::v0::events<E>&>(const ureact::v0::context &,const ureact::v0::events<E> &,const ureact::v0::events<E> &)' being compiled [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Ret=ureact::v0::events<int>,
              E=int,
              Source=int
          ]
D:\a\ureact\ureact\tests\src\feature\default_context.cpp(37,37): message : see reference to function template instantiation 'Ret ureact::v0::detail::MergeAdaptor<void>::operator ()<E,E>(const ureact::v0::events<E> &,const ureact::v0::events<E> &) const' being compiled [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Ret=ureact::v0::events<int>,
              E=int
          ]

// ============================================================================================================================================================
// ============================================================================================================================================================
// ============================================================================================================================================================

D:\a\ureact\ureact\include\ureact/adaptor/merge.hpp(41,62): error C2039: 'copy_events_from': is not a member of 'ureact::v0::detail::event_merge_node<E,Source,ureact::v0::unit>::update::<lambda_1>' [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=ureact::v0::unit
          ]
D:\a\ureact\ureact\include\ureact/adaptor/merge.hpp(41,98): message : see declaration of 'ureact::v0::detail::event_merge_node<E,Source,ureact::v0::unit>::update::<lambda_1>' [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=ureact::v0::unit
          ]
D:\a\ureact\ureact\include\ureact/adaptor/merge.hpp(37,45): message : while compiling class template member function 'ureact::v0::detail::update_result ureact::v0::detail::event_merge_node<E,Source,ureact::v0::unit>::update(void)' [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=ureact::v0::unit
          ]
D:\a\ureact\ureact\include\ureact/detail/node_base.hpp(29): message : see reference to class template instantiation 'ureact::v0::detail::event_merge_node<E,Source,ureact::v0::unit>' being compiled [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=ureact::v0::unit
          ]
D:\a\ureact\ureact\include\ureact/detail/node_base.hpp(40,17): message : see reference to function template instantiation 'std::shared_ptr<ureact::v0::detail::event_merge_node<E,Source,ureact::v0::unit>> ureact::v0::detail::create_node<ureact::v0::detail::event_merge_node<E,Source,ureact::v0::unit>,const ureact::v0::context&,const ureact::v0::events<ureact::v0::unit>&,const ureact::v0::events<ureact::v0::unit>&>(const ureact::v0::context &,const ureact::v0::events<ureact::v0::unit> &,const ureact::v0::events<ureact::v0::unit> &)' being compiled [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Source=ureact::v0::unit
          ]
D:\a\ureact\ureact\include\ureact/adaptor/merge.hpp(88,24): message : see reference to function template instantiation 'Ret ureact::v0::detail::create_wrapped_node<ureact::v0::events<ureact::v0::unit>,ureact::v0::detail::event_merge_node<E,Source,ureact::v0::unit>,const ureact::v0::context&,const ureact::v0::events<ureact::v0::unit>&,const ureact::v0::events<ureact::v0::unit>&>(const ureact::v0::context &,const ureact::v0::events<ureact::v0::unit> &,const ureact::v0::events<ureact::v0::unit> &)' being compiled [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Ret=ureact::v0::events<ureact::v0::unit>,
              Source=ureact::v0::unit
          ]
D:\a\ureact\ureact\tests\src\events.cpp(74,40): message : see reference to function template instantiation 'Ret ureact::v0::detail::MergeAdaptor<void>::operator ()<ureact::v0::unit,ureact::v0::unit>(const ureact::v0::events<ureact::v0::unit> &,const ureact::v0::events<ureact::v0::unit> &) const' being compiled [D:\a\ureact\build\tests\src\ureact_test.vcxproj]
          with
          [
              Ret=ureact::v0::events<ureact::v0::unit>
          ]

[YarikTH]

At least work around is quite simple. Using local lambda instead of template method:

    UREACT_WARN_UNUSED_RESULT update_result update() override
    {
        const auto copy_events_from = [this]( const auto& src ) {
            const auto& src_events = get_internals( src ).get_events();
            this->get_events().insert( //
                this->get_events().end(),
                src_events.begin(),
                src_events.end() );
        };

        std::apply(
            [&copy_events_from](
                const events<Values>&... sources ) { ( copy_events_from( sources ), ... ); },
            m_sources );

        return !this->get_events().empty() ? update_result::changed : update_result::unchanged;
    }

[YarikTH]

Done