rails/rails — pull request #15938 by sgrif (2014-06-27 16:25:56+00:00)
Title: Stop using instance exec for type decorators

We are moving this behavior out to an object that we would like to keep
separated from `ActiveRecord::Base`, which means not passing the class
object to it. As such, we need to stop using `instance_exec`, and
instead close over the subclass on global type decorators that are
applied in `Base`.