можно ли сделать что-то подобное ? не найду синтаксис, имеет смысл в следующем примере:

namespace Test
{
    using System.Collections.Generic;

    public class GenericsTest
    {
        public interface ITopic<E> {}

        public delegate void Handler<E>(E e);

        public interface ISubscriber<E>
        {
            void Handle(E e);
        }

        /// <summary>
        /// signatures are parameterized to ensure the compatibility 
        /// of topic and handler: handler is capable to process 
        /// the events published on topic
        /// </summary>
        public interface ISubManager
        {
            void Subscribe<E>(ITopic<E> topic, Handler<E> handler);
            void Unsubscribe<E>(ITopic<E> topic, Handler<E> handler);
        }

        public class TopicS : ITopic<string> {}
        public class TopicI : ITopic<int> {}

        public class HandlerS : ISubscriber<string>
        {
            public void Handle(string s) { }
        }

        public class HandlerI : ISubscriber<int>
        {
            public void Handle(int i) { }
        }

        public class SubAdapter<E>
        {
            public ITopic<E> topic;
            public ISubscriber<E> subscriber;
            public SubAdapter(ITopic<E> topic, ISubscriber<E> subscriber)
            {
                this.topic = topic;
                this.subscriber = subscriber;
            }
        }

        static IList<object> listeners = new List<object>();
        static ISubManager subManager;

        public static void Main(string[] args)
        {

        }

        static void Add<E>(ITopic<E> topic, ISubscriber<E> s)
        {
            listeners.Add(new SubAdapter<E>(topic, s));
            subManager.Subscribe(topic, s.Handle);
        }

        static void Remove<E>(ITopic<E> topic, ISubscriber<E> s)
        {
            // remove from the list: listeners.Remove(s);
            subManager.Unsubscribe(topic, s.Handle);
        }

        /// <summary>
        /// problem is here !!! 
        /// </summary>
        static void RemoveAll()
        {
            foreach (var adapter in listeners)
            {
                SubAdapter<? : object> sa = (SubAdapter<? : object>) adapter;                
                subManager.Unsubscribe(sa.topic, sa.subscriber.Handle);
            }
            listeners.Clear();
        }
    }
}