Extended version of Dispatcher from Greg Young' post http://goodenoughsoftware.net/2013/11/27/how-to-use-partial-application-like-di/

Dispatcher.cs

public class Dispatcher
{
    readonly Dictionary<Type, Func<object, object>> _dictionary = new Dictionary<Type, Func<object, object>>();

    public void Register<TMessage, TResult>(Func<TMessage, TResult> func)
    {
        _dictionary.Add(typeof(TMessage), x => func((TMessage) x));
    }

    public void Register<TMessage>(Action<TMessage> act)
    {
        _dictionary.Add(typeof(TMessage), x =>
        {
            act((TMessage) x);
            return null;
        });
    }

    public TResult Dispatch<TMessage, TResult>(TMessage m)
    {
        Func<object, object> handler;
        if (!_dictionary.TryGetValue(m.GetType(), out handler))
        {
            throw new Exception("cannot map " + m.GetType());
        }
        return (TResult) handler(m);
    }

    public void Dispatch<TMessage>(TMessage m)
    {
        Func<object, object> handler;
        if (!_dictionary.TryGetValue(m.GetType(), out handler))
        {
            throw new Exception("cannot map " + m.GetType());
        }
        handler(m);
    }
}