If we change `std::set<std::string> paths` () to `StringSet paths`, there are a couple benefits:

• It uses a hash table instead of a tree.
• It supports queries like `.count(StringData)`, whereas std::set<std::string> only supports `.count(std::string const&)`, which can require making a copy if you only have a StringData.

However this assumes we don't care about the order of elements in this set. It looks like we are iterating over this set in a few places, which may or may not mean the order matters. For example if we only union/intersect this with other sets, and check membership, then order doesn't matter.

Whoever takes this will need to check whether the order matters or not.