using System;

public class Program

{

    public static void Main()

    {

        var u = new User{Name = "foo"};

        FooBar(u);

        Console.WriteLine("Hello: " + u.Name);

    }

    public static void FooBar(User user) {

        user = new User {Name = "bar"};

    }

    public class User {

        public string Name {get;set;}

    }

}