public class Program

{

    struct S {

        public readonly int X;

        public S(int x) { X = x; }

        public void Evil() {

            this = new S(666);

        }

}

    public static void Main()

    {

        S s = new S(42);

        System.Console.WriteLine(s.X);

        s.Evil();

        System.Console.WriteLine(s.X);

    }

}