Move instance independent code to class method

This silences reek and imho is probably still not
optimal. I tend to dislike introducing new public
class methods if they're only used in one place.

Anyway, this was reek's last low hanging fruit
before the major mapper refactoring. I wanted to
get those out of the way. The code responsible for
the remaining smells will be heavily refactored
soon. We'll see what it looks like afterwards.