using System;

using System.Linq;

using System.Collections.Generic;

​

public class Box

{

    public int Value{get;set;}

}

public class Program

{

    public static void Main()

    {

        var a = new Box{ Value = 2 };

        var b = a;

        PassByValue(a);

        Console.WriteLine($"a.Value = {a.Value}, b.Value = {b.Value}");

        PassByRef(ref a);

        Console.WriteLine($"a.Value = {a.Value}, b.Value = {b.Value}");

    }

    public static void PassByValue(Box b)

    {

        b.Value = 10;

    }

    public static void PassByRef(ref Box b)

    {

        b = new Box { Value = 20 };

    }

}