[Boost-users] shared_ptr invalid covariant return type

24 Jun 2008

      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!

-John