Re: [Boost-users] shared_ptr invalid covariant return type

From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2008-06-24 09:52:24

John skrev:
> This pattern/idiom is well-established:
> 
>   struct A {
>       virtual A*  clone () = 0;
>   };
> 
>   struct B : public A {
>       virtual B*  clone ();
>   };
> 
> 
> But the above does not work when the pointers A* and B* are replaced by 
> shared_ptr<A> and shared_ptr<B>:
> 
>   struct  A {
>      virtual shared_ptr<A> clone () = 0;
>   };
> 
>   struct  B : public A {
>      virtual shared_ptr<B> clone ();
>   };
> 
> 
> Is there a workaround? Another way to solve the same problem? Thanks!

Well, don't use shared_ptr here. A newly created clone is not shared, 
and it makes the interface less usable in other context to return a 
shared ptr here.

-Thorsten