Subject backed in-memory message broker

MemBroker.cs

    class MemBroker : IDisposable
    {
        private readonly Subject<object> s = new Subject<object>();

        public IDisposable Register<T>(Action<T> handler)
        {
            return s.Subscribe(o =>
            {
                if (o is T) handler((T)o);
            });
        }

        public void Send<T>(T message)
        {
            s.OnNext(message);
        }

        public void Dispose()
        {
            s.Dispose();
        }
    }