C++ Overloading -> operator, how does it work? [duplicate]

Question

I was trying to implement a smart pointer class similar to the standard library auto_ptr and accordingly I had to overload the -> operator for the same. Here is my code

template <typename T>
class SmartPtr
{

   T * operator -> ()
  {
    return _pAct;
  }

 private:
 T * _pAct;
};

Rest of the implementation is not shown so as to avoid diversion from my query.

Now I create a SmartPtr of class A and call a method Show() present in A on it :

SmartPtr smPtr(new A);
smPtr->Show();

Here is my query(don't know if its valid also)

Since SmartPtr::operator->() return A*, the call to show should translate to (A*)Show. Why it translates to (A*)->Show() ?

or in other words how does smPtr->Show() mean call Show() on whatever smPtr->() operator returns ?

Luchian Grigore · Accepted Answer · 2012-10-04 09:21:15Z

4

Because operator -> applies sequentially until it can't be applied any more.

13.5.6 Class member access [over.ref]

1) operator-> shall be a non-static member function taking no parameters. It implements class member access using -> postfix-expression -> id-expression An expression x->m is interpreted as (x.operator->())->m for a class object x of type T if T::operator->() exists and if the operator is selected as the best match function by the overload resolution mechanism (13.3). (emphasis mine)

Which means, in your case, it translates to:

smPtr.operator->()->Show();
          |           |
      returns A*   call Show on the A*

answered Oct 4, 2012 at 9:21

Luchian Grigore

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