And what's wrong with just shared_ptr<B>? Why do you need the additional level of indirection?
For example
int main() { shared_ptr<B> p(new D1); shared_ptr<B> user1 = p; // User1 uses p p.reset(new D2); // p changes pointed type to D2, user1 still points to D1 return 0; }
or
int main() { shared_ptr<B> p(new D1); shared_ptr<B>* user2 = &p; // User2 uses p, but the p.use_count() is still 1. p.reset(new D2); // p changes pointed type to D2, *user2 points to D1 return 0; }
Ok, so you actually want the following: 1) The container itself shouldn't have "strong" references to your objects 2) An object can be recreated/replaced when it doesn't have any strong references. Am I right? If so, store weak_ptr<Base> in your container: // pseudo-code int main() { multi_index_container< weak_ptr<B>, // some indices
container; shared_ptr<B> p(new D1); container.insert(p);
// at some futher stage: auto iterator = container.find(someKey); auto p = iterator->lock(); // if the weak_ptr expired, i.e. no other clients use object, you may re-create it if (!p) recreateIt(); } Note, however, that there's one pitfall here: if weak_ptr expiration affects the keys, you'll have to "refresh" MIC indices somehow.