A pattern idea using mixins to develop game engines in C++.

mixin_game.cpp

#include <iostream>
#include <string>

using namespace std;

// Entity Base Class
class Entity
{
protected:
    int _x;
    int _y;

public:
    void setX(int value)
    {
        _x = value;
    }

    void setY(int value)
    {
        _y = value;
    }

    int getX()
    {
        return _x;
    }

    int getY()
    {
        return _y;
    }
};

// Health Mixin
template <class Base>
class Health : public Base
{
protected:
    int _health;
    int _maxHealth;

public:
    void setHealth(int initialHealth, int maxHealth)
    {
        _health = initialHealth;
        _maxHealth = maxHealth;
    }

    int getHealth()
    {
        return _health;
    }

    void increaseHealth(int value)
    {
        if (_health + value > _maxHealth)
            _health = _maxHealth;
        else
            _health += value;
    }

    void decreaseHealth(int value)
    {
        if (_health - value < 0)
            _health = 0;
        else
            _health -= value;
    }
};

// Mana Mixin
template <class Base>
class Mana : public Base
{
protected:
    int _mana;
    int _maxMana;

public:
    void setMana(int initialMana, int maxMana)
    {
        _mana = initialMana;
        _maxMana = maxMana;
    }

    int getMana()
    {
        return _mana;
    }

    void increaseMana(int value)
    {
        if (_mana + value > _maxMana)
            _mana = _maxMana;
        else
            _mana += value;
    }

    void decreaseMana(int value)
    {
        if (_mana - value < 0)
            _mana = 0;
        else
            _mana -= value;
    }
};

// 4-Way Movement Mixin
template <class Base>
class FourWayMovement : public Base
{
public:
    void moveUp(int steps = 1)
    {
        _y -= steps;
    }

    void moveDown(int steps = 1)
    {
        _y += steps;
    }

    void moveLeft(int steps = 1)
    {
        _x -= steps;
    }

    void moveRight(int steps = 1)
    {
        _x += steps;
    }
};

// The Player
class Player : public FourWayMovement<Health<Mana<Entity> > >
{
    // Player logic
public:
    string whoami()
    {
        return "I'm a Player!";
    }
};

// A Monster
class Monster : public FourWayMovement<Health<Entity> >
{
    // Monster logic
public:
    string whoami()
    {
        return "I'm a Monster!";
    }
};

// A Rock
class Rock : public FourWayMovement<Entity>
{
    // Rock logic
public:
    string whoami()
    {
        return "I'm a Rock!";
    }
};

int main(int argc, char **argv)
{
    Rock rock;
    Monster monster;
    Player player;

    cout << rock.whoami() << endl;
    rock.setX(1);
    rock.setY(10);
    rock.moveDown(5);
    cout << "I'm at X=" << rock.getX() << " Y=" << rock.getY() << endl << endl;

    cout << monster.whoami() << endl;
    monster.setX(15);
    monster.setY(21);
    monster.moveRight(3);
    cout << "I'm at X=" << monster.getX() << " Y=" << monster.getY() << endl;
    monster.setHealth(10, 10);
    monster.decreaseHealth(3);
    cout << "My health is " << monster.getHealth() << endl << endl;

    cout << player.whoami() << endl;
    player.setX(5);
    player.setY(5);
    player.moveUp(1);
    player.moveRight(1);
    cout << "I'm at X=" << player.getX() << " Y=" << player.getY() << endl;
    player.setHealth(15, 25);
    player.increaseHealth(5);
    cout << "My health is " << player.getHealth() << endl;
    player.setMana(10, 20);
    player.increaseMana(2);
    cout << "My mana is " << player.getMana() << endl << endl;

    return 0;
}