using System;

public class Program

{

    public class Container<T, TChild>

        where TChild : Container<T, TChild>

    {

        private T item;

        public T Item 

        { 

            get { return item; }

            set 

            { 

                item = value;

                OnItemChanged?.Invoke((TChild)this);

            } 

        }

        public Action<TChild> OnItemChanged { get; set; }

    }

    public class IntContainer : Container<int, IntContainer> 

    { 

        public void DoIntStuff() 

        {

            Console.WriteLine($"The new item value is {42 - Item} away from 42.");

        }

    }

    public static void Main()

    {

        var c = new IntContainer { Item = 39, OnItemChanged = HandleItemChanged };

        c.Item++;

        c.Item++;

        c.Item++;

    }

    private static void HandleItemChanged(IntContainer c) 

    { 

        c.DoIntStuff();

    }

}