cocos2dx中所有物件都繼承於Ref，或者繼承於 Ref和Clonable
Ref中就是維護了一個計數器，用於判斷該繼承於Ref的物件是否應該delete

class CC_DLL Ref
{
public:

	//計數加1
    void retain();
    
	//計數減1，如果為0，刪除物件
    void release();

	//新增到物件池中，別忘了PoolManager（物件池管理器） 管理AutoreleasePool（物件池），AutoreleasePool管理Ref
    Ref* autorelease();

	//得到當前的計數
    unsigned int getReferenceCount() const;
    
protected:
    
	//建立時計數設為1
    Ref();
    
public:
 
    virtual ~Ref();
    
protected:
    /// count of references
	//計數變數
    unsigned int _referenceCount;
    
	//友元類
    friend class AutoreleasePool;
    
#if CC_ENABLE_SCRIPT_BINDING
public:
    /// object id, ScriptSupport need public _ID
    unsigned int        _ID;
    /// Lua reference id
    int                 _luaID;
#endif
};