Refinements have been pared back to a much more reasonable form that does not have performance implications for unrefined code. They will ship as an official feature in 2.1.

We need to implement refinements in JRuby, at least as an experiment, as soon as possible to know whether they have undiscovered issues. Once they ship in 2.1 it will be much harder to fix them.

I'm marking this for 1.7.6, since I want to do the experiment ASAP.

https://bugs.ruby-lang.org/projects/ruby-trunk/wiki/RefinementsSpec