Jake Arkinstall via Std-Proposals:
> Immediate thought: this doesn't make sense to me. Can you provide a more
> detailed description of your particular use case?

It's simple really. In case of standard library there is std::ios then
virtual inheritance by std::ostream and then regular inheritance by
std::ostringstream.

So client code takes reference to std::ostream and prints to it. My
library works the same way.