Recmap Tentative Idea

recmap.cc

#include <unordered_map>

struct RecMap
{
    using Map = std::unordered_map<int, RecMap*>;
    Map M;
};

int main(int argc, char* argv[])
{
    RecMap RM0;
    RM0.M[1] = nullptr;

    RecMap RM1;
    RM1.M[3] = &RM0;

    return 0;
}