1>C:\src\third-party\boost\boost/unordered/detail/allocator_helpers.hpp(280): error C2027: use of undefined type 'boost::type'
1>          C:\src\third-party\boost\boost/type.hpp(14) : see declaration of 'boost::type'
1>          C:\src\third-party\boost\boost/unordered/detail/allocator_helpers.hpp(436) : see reference to class template instantiation 'boost::unordered::detail::has_select_on_container_copy_construction<T>' being compiled
1>          with
1>          [
1>              T=std::allocator<boost::unordered::detail::ptr_node<std::pair<const int,int>>>
1>          ]
1>          C:\src\third-party\boost\boost/unordered/detail/allocator_helpers.hpp(434) : while compiling class template member function 'std::allocator<_Ty> boost::unordered::detail::allocator_traits<Alloc>::select_on_container_copy_construction(const Alloc &)'
1>          with
1>          [
1>              _Ty=boost::unordered::detail::ptr_node<std::pair<const int,int>>,
1>              Alloc=std::allocator<boost::unordered::detail::ptr_node<std::pair<const int,int>>>
1>          ]
1>          C:\src\third-party\boost\boost/unordered/detail/unique.hpp(106) : see reference to class template instantiation 'boost::unordered::detail::allocator_traits<Alloc>' being compiled
1>          with
1>          [
1>              Alloc=std::allocator<boost::unordered::detail::ptr_node<std::pair<const int,int>>>
1>          ]
1>          C:\src\third-party\boost\boost/unordered/detail/unique.hpp(150) : see reference to class template instantiation 'boost::unordered::detail::pick_node<A,T>' being compiled
1>          with
1>          [
1>              A=std::allocator<std::pair<const int,int>>,
1>              T=std::pair<const int,int>
1>          ]
1>          C:\src\third-party\boost\boost/unordered/unordered_map.hpp(66) : see reference to class template instantiation 'boost::unordered::detail::map<A,K,H,P>' being compiled
1>          with
1>          [
1>              A=std::allocator<std::pair<const int,int>>,
1>              K=int,
1>              H=boost::hash<int>,
1>              P=std::equal_to<int>
1>          ]
1>          C:\src\code\group_by_op_factories.cpp(88) : see reference to class template instantiation 'boost::unordered::unordered_map<K,T>' being compiled
1>          with
1>          [
1>              K=int,
1>              T=int
1>          ]
1>          C:\src\code\group_by_op_factories.cpp(119) : see reference to class template instantiation 'code::`anonymous-namespace'::GroupBy1In<T>' being compiled
1>          with
1>          [
1>              T=int
1>          ]