A showcase of union in C#. Ha-ha.

Union.cs

using System;
using System.Runtime.InteropServices;

namespace ConsoleApp77
{
    class User
    {
        public string Name { get; set; }
        public string Surname { get; set; }
        public string Password { get; set; }
    }

    class UserDTO
    {
        public string Name { get; set; }
        public string Surname { get; set; }
    }

    [StructLayout(LayoutKind.Explicit)]
    struct MyDuck
    {
        [FieldOffset(0)]
        public User User;

        [FieldOffset(0)]
        public UserDTO UserDTO;
    }

    class Program
    {
        static void Main(string[] args)
        {
            var user = new User
            {
                Name = "Vassily",
                Surname = "Poopkeen",
                Password = "12345"
            };
            var duck = new MyDuck
            {
                User = user
            };
            UserDTO dto = duck.UserDTO; // works! :D
            Console.WriteLine(dto.Name); // Vassily
            Console.WriteLine(dto.GetType()); // ConsoleApp77.User ?!
        }
    }
}