prototype_pattern.cpp

#include <iostream>

class Monster
{
public:
    virtual void attack() = 0;
};

class Ghost : public Monster
{
public:
    void attack() override { std::cout << "Ghost attacked!" << std::endl; }
};

class Demon : public Monster
{
public:
    void attack() override { std::cout << "Demon attacked!" << std::endl; }
};

class Spawner
{
public:
    virtual ~Spawner() {}
    virtual Monster *spawnMonster() = 0;
};

template <class T>
class SpawnerFor : public Spawner
{
public:
    Monster *spawnMonster() override { return new T(); }
};

int main()
{
    Spawner *ghostSpawner = new SpawnerFor<Ghost>();
    Spawner *demonSpawner = new SpawnerFor<Demon>();
    Monster *ghost = ghostSpawner->spawnMonster();
    Monster *demon = demonSpawner->spawnMonster();
    ghost->attack();
    demon->attack();
}

Game Programming Patterns

• プロトタイプパターンといいつつ、C++であればtemplateを使う方が良い
• templateなどがサポートされていない環境、たとえばjsonでデータを保存するような場合はいまだに価値がある