Polymorphic generics (or something similar)

Question

I'm not really sure how to word what I want, so I'll just show the code that isn't working:

abstract class EventListener<T> where T : IEvent
{
}

interface IEvent
{
}

/*
 * Simplified a bit, normally this class would use a dictionary of event listeners
 */
class Manager
{
    private EventListener<IEvent> listener;

    public void RegisterListener<T>(EventListener<T> subject) where T : IEvent
    {
        // here is the issue
        listener = subject;
    }
}

/*
 *  Implementation
 */

class FooEvent : IEvent
{
}

class FooListener : EventListener<FooEvent>
{
}

The issue occurs when I try to assign subject to listener. I tried casting before assigning, but had a similar problem:

EventListener<IEvent> casted = subject as EventListener<IEvent>;
events.Add(typeof(T), casted);

Is there a way to make this work?

Answer 1

1. Add non-generic interface IEventListener:

   interface IEventListener
   { }
   

2. Implement it by your EventListener<T> class:

    abstract class EventListener<T> : IEventListener where T : IEvent
   {
   }
   

3. Change your Manager.listener field type to IEventListener:

   private IEventListener listener;