But be careful, sometimes namespace::autoclean doesn't work as one would think.

tl;dr: namespace::autoclean relies on Class::MOP::Class::get_method_list to get the list of methods and removes everything else from the namespace. Unfortunately, the subroutine lists e.g. constants imported from the POSIX module. So, using namespace::clean, which is more explicit, might be cleaner (no pun intended).