Decorator Pattern

Time for Decorator pattern:

Use Espresso, DarkRoast and HouseBlend coffee as the ConcreteComponent, Soy, Mocha and Whip as the ConcreteDecorate.

Here is the code:

using System;

namespace DecoratorPattern
{
    class Program
    {
        static void Main(string[] args)
        {
            Beverage beverage = new Espresso();
            Console.WriteLine(beverage.GetDescription() + " $" + beverage.Cost());

            Beverage beverage2 = new HouseBlend();
            beverage2 = new Mocha(beverage2);
            Console.WriteLine(beverage2.GetDescription() + " $" + beverage2.Cost());

            Beverage beverage3 = new DarkRoast();
            beverage3 = new Whip(beverage3);
            beverage3 = new Soy(beverage3);
            beverage3 = new Soy(beverage3);
            Console.WriteLine(beverage3.GetDescription() + " $" + beverage3.Cost());

            Beverage beverage4 = new Espresso();
            beverage4 = new Soy(beverage4);
            Console.WriteLine(beverage4.GetDescription() + " $" + beverage4.Cost());
        }
    }
}

namespace DecoratorPattern
{
    public abstract class Beverage
    {
        protected string description = "Unknown beverage";
        public virtual string GetDescription()
        {
            return description;
        }

        public abstract double Cost();

    }
}

namespace DecoratorPattern
{
    public abstract class CondimentDecorator : Beverage
    {
    }
}

namespace DecoratorPattern
{
    public class Espresso: Beverage
    {
        Beverage beverage;
        public Espresso()
        {
            description = "Espresso";
        }

        public override double Cost()
        {
            return 2.11;
        }
    }
}

namespace DecoratorPattern
{
    public class DarkRoast:Beverage
    {
        public DarkRoast()
        {
            description = "DarkRoast";
        }
        public override double Cost()
        {
            return .11;
        }
    }
}

namespace DecoratorPattern
{
    public class HouseBlend:Beverage
    {
        public HouseBlend()
        {
            description = "HouseBlend";
        }
        public override double Cost()
        {
            return .99;
        }
    }
}

namespace DecoratorPattern
{
    public class Whip:Beverage
    {
        Beverage beverage;
        public Whip(Beverage beverage)
        {
            this.beverage = beverage;
        }
        public override string GetDescription()
        {
            return beverage.GetDescription() + ", Whip";
        }
        public override double Cost()
        {
            return beverage.Cost() + .11;
        }

    }
}

namespace DecoratorPattern
{
    public class Soy:Beverage
    {
        Beverage beverage;
        public Soy(Beverage beverage)
        {
            this.beverage = beverage;
        }
        public override string GetDescription()
        {
            return beverage.GetDescription() + ", Soy ";
        }
        public override double Cost()
        {
            return beverage.Cost() + .33;
        }
    }
}

namespace DecoratorPattern
{
    public class Mocha:CondimentDecorator
    {
        Beverage beverage;
        public Mocha(Beverage beverage)
        {
            this.beverage = beverage;
        }
        public override string GetDescription()
        {
            return beverage.GetDescription() + ", Mocha ";
        }
        public override double Cost()
        {
            return beverage.Cost() + .02;
        }
    }
}

The diagram from here.

You can find the details of the decription from Head First Design Patterns.