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Mr. Lidström and I had an argument :) Mr. Lidström's claim is that a construct shared_ptr<Base> p(new Derived); doesn't require Base to have a virtual destructor: Armen Tsirunyan : "Really? Will the shared_ptr clean up correctly? Could you please in this case demonstrate how that effect could be implemented?" Daniel Lidström : "The shared_ptr uses its own destructor to delete the Concrete instance. This is known as RAII within the C++ community. My advice is that you learn all you can about RAII. It will make your C++ coding so much easier when you use RAII in all situations." Armen Tsirunyan : "I know about RAII, and I also know that eventually the shared_ptr destructor may delete the stored px when pn reaches 0. But if px had static type pointer to Base and dynamic type pointer to Derived , then unless Base has a virtual destructor, this will result in undefined behavior. Correct me if I am wrong." Daniel Lidström : "The shared_ptr knows the static type is Concrete. It knows this since I passed it in its constructor! Seems a bit like magic, but I can assure you it is by design and extremely nice." So, judge us. How is it possible (if it is) to implement shared_ptr without requiring polymorphic classes to have virtual destructor?

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