4_Prototype 原型

#Prototype

```
// 不好的做法
    monster
        ghost
        demon
        sorcerer
        
class Spawner
{
public:
  virtual ~Spawner() {}
  virtual Monster* spawnMonster() = 0;
};

class GhostSpawner : public Spawner
{
public:
  virtual Monster* spawnMonster()
  {
    return new Ghost();
  }
};

```

原型可以spawn出一个类似自己的物件(克隆)

``` 
class Monster
{
public:
  virtual ~Monster() {}
  virtual Monster* clone() = 0;

  // Other stuff...
};

class Ghost : public Monster {
public:
  Ghost(int health, int speed)
  : health_(health),
    speed_(speed)
  {}

  virtual Monster* clone()
  {
    return new Ghost(health_, speed_);
  }

private:
  int health_;
  int speed_;
};

// 这样只需要一个spawn类
class Spawner
{
public:
  Spawner(Monster* prototype)
  : prototype_(prototype)
  {}

  Monster* spawnMonster()
  {
    return prototype_->clone();
  }

private:
  Monster* prototype_;
};


Monster* ghostPrototype = new Ghost(15, 3);
Spawner* ghostSpawner = new Spawner(ghostPrototype);

//template
Spawner* ghostSpawner = new SpawnerFor<Ghost>();

```