The bounty expires in 7 days. Answers to this question are eligible for a +50 reputation bounty. αλεχολυτ wants to draw more attention to this question. The following code compiles well for Visual Studio < 17.2: #include <optional> #include <map> class __declspec(dllexport) A { using M = std::map<int, A>; std::optional<M> map_; }; But failed for […]