[swift-evolution] Enums and Source Compatibility

[David Hart]

> On 18 Sep 2017, at 19:20, Jordan Rose <jordan_rose at apple.com> wrote:
> 
> That's pretty much the same as this proposal except you don't have the new keyword. I'm not sure why that really makes a difference, since they're obviously paired, and it would limit existing libraries from declaring exhaustive enums until they've moved entirely to Swift 5 mode. I think the current proposal makes sense as is.

The difference is that it reduces the keyword soup and removes a keyword that will be the default behavior enums have in Swift 5. If we follow the same reasoning, why don’t we have nonfinal, @nonescaping, @nonDiscardableResult? Is it really worth adding a keyword only to support libraries while they transition to Swift 5?

> Jordan
> 
> 
>> On Sep 16, 2017, at 01:55, David Hart <david at hartbit.com> wrote:
>> 
>> I’m still very much bothered by having 2 new keywords. I would really prefer the following plan:
>> 
>> Exhaustive by default in Swift 4
>> No new keyword in Swift 4 to change that behaviour
>> Non-exhaustive by default outside the module in Swift 5
>> exhaustive keyword to change the default behaviour
>> 
>> Like that, we don’t need nonexhaustive.
>> 
>> Thoughts?
>> David.
>> 
>>> On 13 Sep 2017, at 21:16, Jordan Rose via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> Proposal updated, same URL: https://github.com/jrose-apple/swift-evolution/blob/non-exhaustive-enums/proposals/nnnn-non-exhaustive-enums.md.
>>> 
>>> Thanks again for all the feedback so far, everyone!
>>> Jordan
>>> 
>>> 
>>>> On Sep 12, 2017, at 17:55, Jordan Rose via swift-evolution <swift-evolution at swift.org> wrote:
>>>> 
>>>> Sorry, I got distracted by other tasks! Both the discussion here and within Apple has moved towards making "non-exhaustive" the default, which, to be honest, I too think is the best design. I'll update the proposal today to reflect that, though I still want to keep both the "nonexhaustive" and "exhaustive" keywords for Swift 4 compatibility for now (or whatever we end up naming them). The compatibility design is a little less ambitious than Brent's; as currently proposed, Swift 4 mode continues to default to 'exhaustive' all the time, even in the actual Swift 5 release.
>>>> 
>>>> I still want to respond to Brent's points directly, but I think you and Vladimir have done a good job discussing them already. I'll send out the updated proposal tomorrow, after I have a little more time to think about #invalid.
>>>> 
>>>> Thanks for putting time into this!
>>>> Jordan
>>>> 
>>>> 
>>>>> On Sep 9, 2017, at 17:34, Rod Brown <rodney.brown6 at icloud.com> wrote:
>>>>> 
>>>>> Jordan,
>>>>> 
>>>>> Do you have any other thoughts about the ongoing discussion here, especially regarding Chris’ comments? As you’re the one pushing this forward, I’d really like to know what your thoughts are regarding this?
>>>>> 
>>>>> - Rod
>>>> 
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> 
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