design_pattern_strategy

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This post implement strategy pattern, described in <Head First Design Pattern>.Strategy Pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it. The class structure is as follows

class FlyBehavior{public:    virtual void fly() = 0;};class FlyWithWings : public FlyBehavior{public:    virtual void fly(){        std::cout << "I am flying!" << std::endl;    }};class FlyNoWay : public FlyBehavior{public:    virtual void fly(){        std::cout << "I cannot fly!" << std::endl;    }};class QuackBehavior{public:    virtual void quack() = 0;};class Quack : public QuackBehavior{public:    virtual void quack(){        std::cout << "Quack!" << std::endl;    }};class Suqeak : public QuackBehavior{public:    virtual void quack(){        std::cout << "Quqeak!" << std::endl;    }};class MuteQuack : public QuackBehavior{public:    virtual void quack(){        std::cout << "MuteQuack!" << std::endl;    }};class Duck{protected:    FlyBehavior* fb;    QuackBehavior* qb;public:    Duck(){        fb = NULL;        qb = NULL;    }    Duck(FlyBehavior* fb_, QuackBehavior* qb_){        fb = fb_;        qb = qb_;    };    Duck(const Duck& duck){        this->fb = duck.fb;        this->qb = duck.qb;    };    void operator=(const Duck& duck){        this->fb = duck.fb;        this->qb = duck.qb;    };    virtual void performQuack() const = 0;    virtual void performFly() const = 0;    virtual void display() const = 0;    void swim(){        std::cout << "Swimming!" << std::endl;    };    void setFlyBehavior(FlyBehavior* fb_){        fb = fb_;    }    void setQuackBehavior(QuackBehavior* qb_){        qb = qb_;    }    virtual ~Duck(){        delete qb;        delete fb;        fb = NULL;        qb = NULL;    }};class ModelDuck : public Duck{public:    ModelDuck() : Duck(){}    ModelDuck(FlyBehavior* fb_, QuackBehavior* qb_){        fb = fb_;        qb = qb_;    }    void performQuack() const {        qb->quack();    }    void performFly() const {        fb->fly();    }    void display() const {        std::cout << "I am one model duck:)" << std::endl;    }};

The main function is as follows

#include <iostream>#include <memory>#include <./duck.hpp>int main(){    FlyNoWay* fb = new FlyNoWay();    MuteQuack* qb = new MuteQuack();    ModelDuck ducky = ModelDuck(fb, qb);    ducky.performFly();    ducky.performQuack();    delete fb;    fb = NULL;    delete qb;    qb = NULL;    return 0;}

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