using System;

public abstract record XXX

{

    public XXX That { get; init; }

​

    protected XXX()

    {

        That = this;

    }

}

​

public record YYY(string XX): XXX(){};

​

public class Program

{

    public static void Main()

    {

        var y1 = new YYY("1");

        Console.WriteLine("---");

        Console.WriteLine(((YYY)y1.That).XX);

        Console.WriteLine(y1.XX);

        y1 = y1 with { XX = "2" };

        Console.WriteLine("---");

        Console.WriteLine(((YYY)y1.That).XX);

        Console.WriteLine(y1.XX);

    }

}