Statting files with directory_entry

Note

Beware! directory_entry is the most bleeding-edge part of the C++17 <filesystem> library. What I am about to describe is neither implemented by Boost, nor by <experimental/filesystem>.

Retrieving a file's metadata from its inode is done by querying an object of type fs::directory_entry. If you're familiar with the POSIX approach to retrieving metadata, imagine that a fs::directory_entry contains a member of type fs::path and a member of type std::optional<struct stat>. Calling entry.refresh() is, basically, the same thing as calling the POSIX function stat(); and calling any accessor method, such as entry.file_size(), will implicitly call stat() if and only if the optional member is still disengaged. Merely constructing an instance of fs::directory_entry won't query the filesystem; the library waits until you ask a specific question before it acts. Asking a specific question, such as entry.file_size(), may cause the library to query...