[xilun0]

(little nitpicking note : there are cases where it can be useful to have a virtual descriptor as the only virtual method of a class)

[copper]

I'm interested in knowing what these are - barring an alignment-related weirdness, I can't think of any reason to do that.

[xilun0]

If you do everything in the constructor and the destructor, and in the meantime store a generic instance (or maybe a list of generic instances) somewhere.

This can be a quite rare situation, though. But not impossible.