swift234

[Accessibility] Private members cannot override public members.

...unless they are in a private class.

Consider this scenario:

  class Base {
    func foo() -> Base { ... }
  }
  class Sub : Base {
    private override func foo() -> Sub { ... }
  }
  class Grandchild : Sub {
    override func foo() -> Base { ... }
  }

Because Grandchild can't see Sub, its override of foo() looks perfectly
reasonable...but now Sub's expectations for foo() have been broken.

Swift SVN r19769