Can my class know/handle casting?

With assignment and copying you can implement an operator to handle those operations ina custom manner. Is it possible to do the same for casting of pointers? I know that in casting objects I can simply make a constructor that takes the Base type and it'll handle it, but what about pointers?

Code:

class A
{
     virtual void foo() {}
};

class B : public A
{
};

int main()
{
     A* a;
     B* b;

     //Is there a way to write a function in A that will be called when i do either of these?
     b = ( B* ) a;
     b = dynamic_cast<B*> a;
}

Why not just have class A have a virtual copy() function and the equal operator. Then the equal operator will always call the copy() for the most recently defined version of copy().

Originally Posted by master5001

Why not just have class A have a virtual copy() function and the equal operator. Then the equal operator will always call the copy() for the most recently defined version of copy().

The only problem with that is it doesn't handle this case:

Code:

B* b =  new B();

( ( A* ) b )->SomeMethod();

If you need that case then I would imagine something is seriously wrong with your design. As usual, what are you trying to do?

You can overload a conversion. You can not overload a cast.

Ah yes, of course. I misunderstood what you wanted. I betcha can't name a language that does work like that.

it will work if

A *a = new B();

Actually, you can overload a cast. But you can't overload anything for types you didn't define, and pointers all count as built-in types.

Originally Posted by m37h0d

it will work if

A *a = new B();

this apparently is not true if B inherits virtually from A

this apparently is not true if B inherits virtually from A

No, it is still true, as long as public inheritance is used. Of course, in the above code foo() is a private member function.

Originally Posted by CornedBee

Actually, you can overload a cast. But you can't overload anything for types you didn't define, and pointers all count as built-in types.

You can overload dynamic_cast<>, static_cast<>, or const_cast<>? That's what I mean by "cast."

Expressions like (Type1)obj2 are often said to be "casting" obj2 to Type1, but I tend to call it a conversion, not a cast.

Expressions like (Type1)obj2 are often said to be "casting" obj2 to Type1, but I tend to call it a conversion, not a cast.

Yeah, the C++ Standard calls them conversion functions too.

I meant you can overload the conversion abilities, indeed. You can't overload the four cast operators, which, by the way, is a pity.