I assume he means: any gems that monkey-patch any of the built-in classes. I believe ActiveSupport modifies things like Fixnum (1.days.from_now, for example).
Yes. That's what I meant.
Ah. Ok. I was thinking something changing core files on disk.
I bet that's doable ...
Change string.c, recompile, if a gem can execute arbitray code.
Does it really happen at install time or (like in Python) at runtime everytime the package/module/gem is loaded/required?
ActiveSupport doesn't modify the base Ruby classes until it's been loaded. Merely installing gems will not impact anything except disk space.
puppet, facter, rake, mongrel use 'sed' to edit the code on the fly at install time, to set shebang lines etc
There are surely many others, these are just the ones I have at hand as examples.