Very nice, thank you Sean! Do you think is still apropriate to (try to) use this pattern in a tightly coupled hierarchy, where the objects have references to the parent object or to the document? Value semantics for objects in such a hierarchy may not function as well.
Regarding performance, since the concept_t uses virtual dispatch anyway, it should have the same perf characteristic as if the document stores directly the unique_ptr<concept_t>, or am I overseeing something?
Charles, I've downloaded the High Quality WMV and it doesn't get past the first 15/20minutes. It just springs at the beginning. The same problem I've had with the c++ and beyond panel video. I am not sure if this is a video issue or download issue, but you may want to check it.