using System;

public class Program

{

    struct Test

    {

        public int a;

    }

    static void updateTest(ref Test t) {

        t.a = 42;

    }

    public static void Main()

    {

        Test myObj = new Test();

        updateTest(ref myObj);

​

        Console.WriteLine(string.Format("{0}", myObj.a));

    }

}