Policy-based design example

MailNotification.h

#include "Notification.h"

#include <string>
#include <iostream>

class MailNotification : public Notification
{
public:
	void notify(const std::string& mSubject) override
	{
		std::string show("Mail ");
		show.append(mSubject);

		std::cout << show << "\n";
	}
};

Notification.h

#ifndef NOTIFICATION_H
#define NOTIFICATION_H

#include <string>

class Notification
{
public:
	virtual void notify(const std::string& mSubject) = 0;
};

#endif // NOTIFICATION_H

Strategy.h

#include <iostream>

#include "User.h"
#include "WAppNotification.h"
#include "MailNotification.h"

int main()
{
	User<WAppNotification> user;
	user.send("primer mensaje");
	
	User<MailNotification> user2;
	user2.send("segundo mensaje");
}

User.h

#ifndef USER_H

#include "Notification.h"

#include <string>

template<class T>
class User
{
private:
	T _notification;

public:
	User()
	{
		static_assert(std::is_base_of<Notification, T>::value, "T tiene que heredar de Notificación.");
	}
	~User()
	{
	}

	void send(const std::string& mSubject)
	{
		//Solo envia las notificaciones bien a Mail
		_notification.notify(mSubject);
	}
};

#endif

WaAppNotification.h

#ifndef WAPPNOTIFICATION_H
#define WAPPNOTIFICATION_H

#include "Notification.h"

#include <string>
#include <iostream>

class WAppNotification : public Notification
{
public:
	void notify(const std::string& mSubject) override
	{
		std::string show("Whatsapp ");
		show.append(mSubject);

		std::cout << show << "\n";
	}
};
#endif // WAPPNOTIFICATION_H