Re: class member access operator (->) overloading

From:

Victor Bazarov <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Tue, 12 May 2009 09:52:48 -0400

Message-ID:

<gubuum$r4r$1@news.datemas.de>

Arkaitz Jimenez wrote:

For what I've seen around the operator-> is normally overloaded to
return the inner pointer in the case of a SmartPointer template.
However I was wondering if there is any way of having control after
the access was done, you can always execute code before returning the
pointer but obviously you can't after return.
So, is there anyway to get control before and after operator-> has its
effect?

If I understand correctly what you're after, then no. The overloaded
operator-> returns something (usually a pointer) for which another
operator-> will subsequently be applied. And that's until it's mapped
to the intrinsic operator-> for a pointer to a class object or a pointer
to a non-class object for a pseudo-destructor call.

#include <iostream>
#include <ostream>

using std::cout;

template<class T>
class AuxHasArrow
{
    T* t;
public:
    AuxHasArrow(T* t) : t(t) {}

    T* operator->() { std::cout << "In Aux\n"; return t; }
};

template<class T>
class HasArrow
{
    T* t;
public:
    HasArrow(T* t) : t(t) {}
    AuxHasArrow<T> operator->()
      { std::cout << "In HasArrow\n"; return AuxHasArrow<T>(t); }
};

struct A {
    int a;
};

int main()
{
    A a = { 42 };
    HasArrow<A> ha(&a);

    cout << ha->a << "after all\n";
}

See, there is nothing you can squeeze in your class to capture the
control after the operator-> is applied to the address of the 'a' object
(to extract that 42 for output).

V
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