Method handle

benchmark/complex/variant.cpp:134–139

               S47, S48, S49, S50> state;
public:
  void handle(const e1&) {
    std::visit(overload{
        [&](S1) { if (guard()) action(); state = S2{}; },
        [](auto) { }
    }, state);
  }

  void handle(const e2&) {
    std::visit(overload{