gistfile1.txt

namespace crap
{
    using System;
    using System.Collections.Generic;
    using System.Data;
    using System.Data.SqlClient;

    public class PartialAppPlayground
    {
        private static Dispatcher<IHandlerResult> _dispatcher;

            public static void Main()
            {
                Initialize();
                Console.WriteLine(_dispatcher.Dispatch(new UsersByLastNameQuery()));
            }

        public static void Initialize()
        {
            _dispatcher = new Dispatcher<IHandlerResult>();
            Func<IDbConnection> createTestConnection = () => new SqlConnection();
            _dispatcher.Register<UsersByLastNameQuery>(message => UsersByLastNameQueryHandler.Handle(message, createTestConnection));
            //note this is using an object return you can change it to use TReturn as well 
            //in much the same way that the first argument works.
        }
    }

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

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

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

    public class UsersByLastNameQuery : IMessage
    {
        public string LastName { get; set; }
    }

    public class UsersByLastNameQueryHandler
    {
        public static UsersByLastNameQueryResult Handle(UsersByLastNameQuery query, Func<IDbConnection> createConnection)
        {
            using (var connection = createConnection())
            {
                //SQL
                return new UsersByLastNameQueryResult();
            }
        }
    }

    public class UsersByLastNameQueryResult : IHandlerResult
    {
    }

    public interface IMessage
    {
    }

    public interface IHandlerResult
    {
    }
}