using System;

public class Program

{

    abstract class Beverage 

    {

        public abstract int Cost();

    }

    abstract class AddOnDecorator : Beverage

    {

        public abstract override int Cost();

    }

    //This is not such a great example.

    //

    //You would typically use this pattern when:

    //1. You do not have access to the base class source code

    //2. Don't want to change the base class

    //3. When you want to deprecate a class.

    class CaramelDecorator : AddOnDecorator 

    {

        Beverage myBeverage = null;

        public CaramelDecorator(Beverage beverage)

        {

            myBeverage = beverage;

        }

        public override int Cost()

        {

            return myBeverage.Cost() + 1;

        }

    }

​

    class WhippedCreamDecorator : AddOnDecorator 

    {

        Beverage myBeverage = null;

        public WhippedCreamDecorator(Beverage beverage)

        {

            myBeverage = beverage;

        }

        public override int Cost()

        {

            return myBeverage.Cost() + 2;

        }

    }

​

    class Espresso : Beverage 

    {

        public Espresso()

        {

        }

        public override int Cost()

        {

            return 1;

        }

    }

    public static void Main()

    {

        var myDrink = new Espresso();

        var myCaramelEspresso = new CaramelDecorator(myDrink);

        var myCaramelEspressoWithWhippedCream = new WhippedCreamDecorator(myCaramelEspresso);

        Console.WriteLine("My drink now costs {0}", myCaramelEspressoWithWhippedCream.Cost());

    }

}