using System;

using System.Text;

public class Program

{

    public static void Main()

    {

        var mainBuilder = new StringBuilder();

        PassByReference1(mainBuilder);

        Console.WriteLine("after PassByReference1: mainBuilder = {0}", mainBuilder);

        PassByReference2(ref mainBuilder);

        Console.WriteLine("after PassByReference2: mainBuilder = {0}", mainBuilder);

    }

    static void PassByReference1(StringBuilder builder)

    {

        builder.Append("modified1");

        builder = new StringBuilder("new1"); // this change is local to this method

    }

    static void PassByReference2(ref StringBuilder builder)

    {

        builder.Append("modified2");

        builder = new StringBuilder("new2");

    }

}

​