Aliasing Structs in C++11

Question

I am writing a C++11 program that involves events and callbacks. I have a base class called Event, it's then derived by concrete event classes.

template <typename EventArgs>
class Event {
public:
    using EventHandler = std::function<void(EventArgs)>;
    void operator +=(EventHandler handlerDelegate);
    void fire(EventArgs e);
private:
    std::vector<EventHandler> subscribers;
};

struct TouchEventArgs { int x, int y }
struct TouchEvent : public Event<TouchEventArgs> { }
...

I was wondering if something like this was possible:

template <typename EventArgs>
using event = struct : public Event<EventName> {  };

So that i could declare events like

event<TouchEventArgs> TouchEvent;

Answer 1

You could maintain a compile-time mapping between event types and their arg types:

namespace detail {
    //primary template
    template <typename EventArgs>
    struct event;

    //the event for TouchEventArgs is TouchEvent
    template<> struct event<TouchEventArgs>
    { using type = TouchEvent; };
}

//helper template
template <typename EventArgs>
using event = typename detail::event<EventArgs>::type;

Now we can declare a variable just like you wanted (assuming the name conflict was an accident):

event<TouchEventArgs> touch_event; //decltype(TouchEvent) is TouchEvent