using System;

public class Program

{

    public static void Main()

    {

        var x = new Lol { Id = 10 };

        Console.WriteLine($"Hello World {x.Id}");

        x.SetValue();

        Console.WriteLine(x.Id);

    }

    public struct Lol 

    { 

        public int Id { get; init; }

    }

}

​

public static class Extensions 

{

    public static Program.Lol SetValue(this ref Program.Lol instance) 

    {

        instance = new Program.Lol { Id = 42 };

        return instance;

    }

}