rails/rails — pull request #10909 by bcardarella (2013-06-11 03:25:18+00:00)
Title: Use symbols instead of strings in ActiveSupport::Concern

ActiveSupport::Concern is used all over Rails
This PR will only create 3 new objects as keys are never recreated and
are not subject to garbage collection.

The strings were being uniquely created and garbage collected. I don't
have any performance numbers but this should be better than all of the
GC.