using System;
using System.Reflection;
using System.Runtime.InteropServices;

namespace ConsoleApplication1
{
    [StructLayout(LayoutKind.Explicit)]
    public struct CatOrDog
    {
        [FieldOffset(0)]
        public Cat Cat;

        [FieldOffset(0)]
        public Dog Dog;
    }


    class Program
    {
        static void Main(string[] args)
        {
            var catOrDog = new CatOrDog { Cat = new Cat { Name = "Jenny" } };
            catOrDog.Dog.Say();
        }
    }

    public class Cat
    {
        public string Name { get; set; }

        public void Say()
        {
            Console.WriteLine("Meow " + Name);
        }
    }

    public class Dog
    {
        public string Name { get; set; }

        public void Say()
        {
            Console.WriteLine("Woof" + Name);
        }
    }
}