c++ 通用handler

template <class T>
class Handle {
public:
    // unbound handle
    Handle(T *p = 0): ptr(p), use(new size_t(1)) { }

    // overloaded operators to support pointer behavior
    T& operator*();
    T* operator->();
    const T& operator*() const;
    const T* operator->() const;

    // copy control: normal pointer behavior, but last Handle deletes the object
    Handle(const Handle& h): ptr(h.ptr), use(h.use)
                                        { ++*use; }
    Handle& operator=(const Handle&);
    ~Handle() { rem_ref(); }
private:
    T* ptr;          // shared object
    size_t *use;     // count of how many Handles point to *ptr
    void rem_ref()
        { if (--*use == 0) { delete ptr; delete use; } }
};

template <class T>
inline Handle<T>& Handle<T>::operator=(const Handle &rhs)
{
    ++*rhs.use;    // protect against self-assignment
    rem_ref();     // decrement use count and delete pointers if needed
    ptr = rhs.ptr;
    use = rhs.use;
    return *this;
}

template <class T> inline T& Handle<T>::operator*()
{
    if (ptr) return *ptr;
    throw std::runtime_error
                   ("dereference of unbound Handle");
}
template <class T> inline T* Handle<T>::operator->()
{
    if (ptr) return ptr;
    throw std::runtime_error
                   ("access through unbound Handle");

}

template <class T> inline
const T& Handle<T>::operator*() const
{
    if (ptr) return *ptr;
    throw std::runtime_error("dereference of unbound Handle");
}
template <class T> inline
const T* Handle<T>::operator->() const
{
    if (ptr) return ptr;
    throw std::runtime_error("access through unbound Handle");

}
int main()
{
{  // new scope
   // user allocates but must not delete the object to which the Handle is attached
   Handle<int> hp(new int(42));
   { // new scope
       Handle<int> hp2 = hp;   // copies pointer; use count incremented
       cout << *hp << " " << *hp2 << endl;   // prints 42 42
       *hp2 = 10;              // changes value of shared underlying int
   }   // hp2 goes out of scope; use count is decremented
   cout << *hp << endl;    // prints 10
}  // hp goes out of scope; its destructor deletes the int
}