// Each subclass should have two members, as we want to separate the ones for Win, Comm, and Datatypes :
// static std::unordered_map<int, smpi_key_elem> keyvals_;
// static int keyval_id_;
// Each subclass should have two members, as we want to separate the ones for Win, Comm, and Datatypes :
// static std::unordered_map<int, smpi_key_elem> keyvals_;
// static int keyval_id_;