Method trigger

example/map/map.cpp:32–39

    template <typename Event>
    void trigger(Event e) const {
        auto is_known_event = hana::contains(map_, e);
        static_assert(is_known_event,
            "trying to trigger an unknown event");

        for (auto& handler : this->map_[e])
            handler();
    }
};

template <typename ...Events>