using System;

public class Program

{

    public static void Main()

    {

        var a = new root("name");

        var b = new extended(a, "surname");

        Console.WriteLine(b);

    }

}

​

public record root (string name);

public record extended (string surname, string name) : root (name)

{

    public extended(root copy, string surname): this(surname, copy.name) { }

}