Nat Goodspeed wrote:

[Nat] <silly question> Could the ref count be put into a virtual base class so that only one instance would appear in a given leaf class, regardless of how many enable_shared_from_this<> bases it has?

Not a silly question at all. Every enable_shared_from_this base contains a weak_ptr, not a reference count. The shared_ptr constructor looks up the enable_shared_from_this base and initializes its weak_ptr accordingly. This doesn't work when there are two or more enable_shared_from_this bases, though. I could put the weak_ptr in a virtual polymorphic base. This would force polymorphism on all clients of enable_shared_from_this... probably acceptable. It will also force a dynamic_pointer_cast in every shared_from_this, and this may be harder to swallow, particularly in cases where RTTI is off. So I'm not sure. If you do want the above behavior, it's easy to duplicate, as I already responded in my first post on the topic. Just make FooB return dynamic_pointer_cast<B>( FooA() ) and remove the enable_shared_from_this<B> base (A needs to be made polymorphic, of course).