#include <unordered_map>
#include <unordered_set>
#include <string>

using Mymap = std::unordered_map<std::string, std::unordered_set<std::string>>;

class A {
    Mymap n_;
public:
    A(Mymap&& n)
        : n_{std::move(n)}
    {}

    A(Mymap& n)
        : n_{n}
    {}

    // doesn't compile
    //template <typename T>
    //A(T<Mymap::value_type>&& n)
    //    : n_{std::forward(n)}
    //{}
};

int main() {
    A a1{{{"C", {"A", "B"}}}};

    Mymap m{{{"C", {"A", "B"}}}};
    A a2{m};
}