Creating the GameObject class

Our game's elements are all physics bodies and will have sprites to represent them visually. It is a common practice to club these two entities together. Cocos2d-x has an inbuilt class to handle this known as PhysicsSprite, but since this is our first physics game, we shall create our own class called GameObject to do the job:

class GameObject : public CCSprite
{
public:
  GameObject() : game_world_(NULL), body_(NULL), 
    type_(E_GAME_OBJECT_NONE) {}
  virtual ~GameObject();

  // returns an autorelease GameObject
  static GameObject* create(GameWorld* game_world, 
    const char* frame_name);

  // accessors & mutators
  inline b2Body* GetBody() { return body_; }
  
  inline EGameObjectType GetType() { return type_; }
  inline void SetType(EGameObjectType type) { type_ = type; }

  virtual void Update()
  {
    // update position of sprite based on position of body
    if(body_)
    {
      setPosition(ccp(WORLD_TO_SCREEN(body_->GetPosition().x), 
...