opencv 智能指针 Ptr

//////////////////// generic_type ref-counting pointer class for C/C++ objects ////////////////////////

/*!
  Smart pointer to dynamically allocated objects.

  This is template pointer-wrapping class that stores the associated reference counter along with the
  object pointer. The class is similar to std::smart_ptr<> from the recent addons to the C++ standard,
  but is shorter to write :) and self-contained (i.e. does add any dependency on the compiler or an external library).

  Basically, you can use "Ptr<MyObjectType> ptr" (or faster "const Ptr<MyObjectType>& ptr" for read-only access)
  everywhere instead of "MyObjectType* ptr", where MyObjectType is some C structure or a C++ class.
  To make it all work, you need to specialize Ptr<>::delete_obj(), like:

  code
  template<> void Ptr<MyObjectType>::delete_obj() { call_destructor_func(obj); }
  endcode

  
ote{if MyObjectType is a C++ class with a destructor, you do not need to specialize delete_obj(),
  since the default implementation calls "delete obj;"}

  
ote{Another good property of the class is that the operations on the reference counter are atomic,
  i.e. it is safe to use the class in multi-threaded applications}
*/
template<typename _Tp> class CV_EXPORTS Ptr
{
public:
    //! empty constructor
    Ptr();
    //! take ownership of the pointer. The associated reference counter is allocated and set to 1
    Ptr(_Tp* _obj);
    //! calls release()
    ~Ptr();
    //! copy constructor. Copies the members and calls addref()
    Ptr(const Ptr& ptr);
    template<typename _Tp2> Ptr(const Ptr<_Tp2>& ptr);
    //! copy operator. Calls ptr.addref() and release() before copying the members
    Ptr& operator = (const Ptr& ptr);
    //! increments the reference counter
    void addref();
    //! decrements the reference counter. If it reaches 0, delete_obj() is called
    void release();
    //! deletes the object. Override if needed
    void delete_obj();
    //! returns true iff obj==NULL
    bool empty() const;

    //! cast pointer to another type
    template<typename _Tp2> Ptr<_Tp2> ptr();
    template<typename _Tp2> const Ptr<_Tp2> ptr() const;

    //! helper operators making "Ptr<T> ptr" use very similar to "T* ptr".
    _Tp* operator -> ();
    const _Tp* operator -> () const;

    operator _Tp* ();
    operator const _Tp*() const;

    _Tp* obj; //< the object pointer.
    int* refcount; //< the associated reference counter
};