Structural Pattern

이미 정의되어 있는 클래스에 특정 메소드를 동적으로 추가하고 싶다.

기본 클래스를 상속받아 decorator 클래스를 만들고 새로 추가될 기능은 decorator 클래스를 상속받아 클래스에 정의한다.

decorator.cpp

#include<string>
#include <iostream>
using namespace std;
 
class Car //Our Abstract base class
{
protected:
	string _str;
public:
	Car()
	{
		_str = "Unknown Car";
	}
 
	virtual string getDescription()
	{       
		return _str;
	}
 
	virtual double getCost() = 0;
 
	virtual ~Car()
	{
		cout << "~Car()\n";
	}
};
 
class OptionsDecorator : public Car //Decorator Base class
{
public:
	virtual string getDescription() =0;
 
	virtual ~OptionsDecorator()
	{
		cout<<"~OptionsDecorator()\n";
	}
};
 
 
class CarModel1 : public Car
{       
public:
	CarModel1()
	{
		_str = "CarModel1";
	}
	virtual double getCost()
	{
		return 31000.23;
	}
 
	~CarModel1()
	{
		cout<<"~CarModel1()\n";
	}
};
 
 
class Navigation: public OptionsDecorator
{
	Car *_b;
public:
	Navigation(Car *b)
	{
		_b = b;
	}
	string getDescription()
	{
		return _b->getDescription() + ", Navigation";
	}
 
	double getCost()
	{
		return 300.56 + _b->getCost();
	}
	~Navigation()
	{
		cout << "~Navigation()\n";
	}
};
 
class PremiumSoundSystem: public OptionsDecorator
{
	Car *_b;
public:
	PremiumSoundSystem(Car *b)
	{
		_b = b;
	}
	string getDescription()
	{
		return _b->getDescription() + ", PremiumSoundSystem";
	}
 
	double getCost()
	{
		return 0.30 + _b->getCost();
	}
	~PremiumSoundSystem()
	{
		cout << "~PremiumSoundSystem()\n";
	}
};
 
class ManualTransmition: public OptionsDecorator
{
	Car *_b;
public:
	ManualTransmition(Car *b)
	{
		_b = b;
	}
	string getDescription()
	{
		return _b->getDescription()+ ", Soy Milk";
	}
 
	double getCost()
	{
		return 0.30 + _b->getCost();
	}
	~ManualTransmition()
	{
		cout << "~ManualTransmition()\n";
	}
};
 
class CarDecoratorExample{
public:
 
	void execute()
	{
		//Create our Car that we want to buy
		Car *b = new CarModel1();
 
		cout << "Base model of " << b->getDescription() << " costs $" << b->getCost() << "\n";  
 
		//Who wants base model lets add some more features
 
		b = new Navigation(b);
		cout << b->getDescription() << " will cost you $" << b->getCost() << "\n";
		b = new PremiumSoundSystem(b);
		b = new ManualTransmition(b);
		cout << b->getDescription() << " will cost you $" << b->getCost() << "\n";
 
 
		delete b;
	}
 
};
 
 
int main()
{
	CarDecoratorExample b;
	b.execute();
	return 0;
}

http://en.wikibooks.org/wiki/C%2B%2B_Programming/Code/Design_Patterns#Decorator