[swift-evolution] [Proposal] Protected Access Level

[Charlie Monroe]

> My answer is this: There is nothing magical about being a subclass that ought to grant access to those methods.

There is - it's a family member that you let use your summer house. Without the metaphor, here is an example for this being useful: 

URLConnection subclass may want to update the URL in case of a redirect, but you don't really want to expose the setter for the URL to public.

> For instance, if your subclass grows very complicated and you extract a helper object, it's perfectly reasonable for that helper object to want to access the "subclass-only" API.

That's what "friend" classes are for in C++, similar concept would be applied here.

> Contrarily, simple subclasses might not need that API, and exposing it to them would be an unnecessary risk. And there are things which you don't subclass at all which could benefit from being hidden away—think of the Objective-C runtime, which has some parts which every app needs (like the definition of `BOOL`) and othe