using System;

​

public static class MowingNad

{

    public static R? AndThen<T, R>(this T? self, Func<T, R?> doThat)

    where R: class {

        if (self is {} something) {

            return doThat.Invoke(something);

        }

        else {

            return null;

        }

    }

    public static R? AndThen<T, R>(this T? self, Func<T, R?> doThat)

    where R: struct {

        if (self is {} something) {

            return doThat.Invoke(something);

        }

        else {

            return null;

        }

    }

}

public class Program

{

    static void Demo<T>(T? opt) {

        var n = opt.AndThen<T, int>(s => 42);

        var s2 = opt.AndThen<T, string>(s => "hey");

        Console.WriteLine("{");

        Console.WriteLine(n);

        Console.WriteLine(s2);

        Console.WriteLine("}\n");

    }

    public static void Main()

    {

        string? s = "hey";

        Demo(s);

        s = null;

        Demo(s);

        int? n = 27;

        Demo(n);

        n = null;

        Demo(n);

    }

}