thoughtbot/guides — pull request #190 by sgrif (2014-06-09 14:44:26+00:00)
Title: Prefer `protected` over `private` for non-public attributes

- With warnings enabled, private attributes cause a warning on MRI
(doubly important for open source libaries, which should not emit
warnings)
- Reduces churn when adding comparison or equality methods, since you'll
likely need to access the attributes of the other object
- Reduces churn when adding a writer, since it is impossible to call
private writer methods.