http://pierovggsterf4w5xplynqtl56srftc242l3g2xloqlty6nv7372xuyd.onion
With my previous assumption on fixed formats, I could do lookups on the set to quickly check if a provided stem was valid. After the changes, this involved a heterogeneous comparison , i.e., a comparison of different types. The trivial way to do this is a linear search, e.g., with std::find and a lambda or a range-based for .