commandRegister

using System;
using System.Collections.Generic;

namespace ConsoleApplication
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var register = new CommandRegister();
            register.Register<AdmitPatient>(cmd => 
            {
                Console.WriteLine($"FirstName: {cmd.FirstName}");
                Console.WriteLine($"Surname: {cmd.Surname}"); 
            });

            var dispatcher = new Dispatcher(register);
            dispatcher.Send(new AdmitPatient("Fredd", "Bloggs"));
        }

        class AdmitPatient
        {
            public string FirstName { get; }

            public string Surname { get; }

            public AdmitPatient(string firstName, string surname)
            {
                FirstName = firstName;
                Surname = surname;
            }
        }
        
        class CommandRegister
        {
            public Dictionary<Type, Action<object>> Handlers { get; }

            public CommandRegister()
            {
                Handlers = new Dictionary<Type, Action<object>>();
            }
            
            public void Register<T>(Action<T> handler) where T : class
            {
                Action<object> action = cmd => 
                {
                    handler(cmd as T);
                };

                Handlers.Add(typeof(T), action);
            }
        }

        class Dispatcher
        {
            CommandRegister register;

            public Dispatcher(CommandRegister register)
            {
                this.register = register;
            }

            public void Send(object message)
            {
                SendGeneric((dynamic)message);
            }

            void SendGeneric<T>(T command)
            {
                register.Handlers[typeof(T)](command);
            }
        }

    }
}