You need a way to define the accessor -- otherwise you'd have to do it just using the raw class variable (`@@cancan_actions`).  `class_attribute` was used over `cattr_accessor` because that is what is used by the active model serializer gem.  I imagine they chose `class_attribute` so that sub-classes can change things without affecting the parent.  See [this article](https://coderwall.com/p/xhcmbg) for a good explanation of the two.