[swift-evolution] final + lazy + fileprivate modifiers

Matthew Johnson matthew at anandabits.com
Sun Feb 12 10:25:23 CST 2017

> On Feb 12, 2017, at 10:19 AM, David Hart via swift-evolution <swift-evolution at swift.org> wrote:
> I was reading this nice listing of Swift keywords (https://medium.com/the-traveled-ios-developers-guide/swift-keywords-v-3-0-1-f59783bf26c#.2s2yis3zh <https://medium.com/the-traveled-ios-developers-guide/swift-keywords-v-3-0-1-f59783bf26c#.2s2yis3zh>) and three of them struck me as potentially not long for this world and I was thinking if we needed/could deprecate them before any kind of ABI stability set in.
> I'm listing them here but it might be worth starting separate discussions for each of them.
> Final
> Can someone tell me what is the use of 'final' now that we have 'public' default to disallowing subclassing in importing modules? I know that 'final' has the added constraint of disallowing subclassing in the same module, but how useful is that? Does it hold its weight? Would we add it now if it did not exist?

Final is used abundantly by the teams I have worked with.  These are iOS apps with no external consumers of the module.  My experience is that it is a very useful communication of intent to future readers of the code.

That aside, I think the criteria for a change are different now.  Your criteria were relevant during the big breaking change era of Swift 3.  I think the criteria for removing a feature at this point should be: is it causing problems that justify the breaking change required to remove it?

> Lazy
> This one is clearer: if Joe Groff's property behaviors proposal from last year is brought forward again, lazy can be demoted from a language keyword to a Standard Library property behavior. If Joe or anybody from the core team sees this: do we have any luck of having this awesome feature we discussed/designed/implemented in the Swift 4 timeframe?
> Fileprivate 
> I started the discussion early during the Swift 4 timeframe that I regret the change in Swift 3 which introduced a scoped private keyword. For me, it's not worth the increase in complexity in access modifiers. I was very happy with the file-scope of Swift pre-3. When discussing that, Chris Latner mentioned we'd have to wait for Phase 2 to re-discuss it and also show proof that people mostly used 'fileprivate' and not the new 'private' modifier as proof if we want the proposal to have any weight. Does anybody have a good idea for compiling stats from GitHub on this subject? First of all, I've always found the GitHub Search quite bad and don't know how much it can be trusted. Secondly, because 'private' in Swift 2 and 3 have different meanings, a simple textual search might get us wrong results if we don't find a way to filter on Swift 3 code.
> Thanks for hearing me out!
> David.
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