On Thu, Jan 4, 2018 at 13:46 Cheyo Jimenez <ch...@masters3d.com> wrote:
> > > On Jan 4, 2018, at 10:49 AM, Jordan Rose <jordan_r...@apple.com> wrote: > > I'll admit I hadn't thought of using "unknown default" (or "default > unknown"). I don't think that's terrible, but I mildly prefer `unknown > case` because it builds on the "pun" that enum elements are also defined > using 'case'. If anything hits this part of the switch, it really will be > an "unknown case", i.e. a statically-unknown enum element. > > To Cheyo's point, if this *were* to be a single token I'd probably spell > it #unknown, like #available. Then we'd have `case #unknown:` and something > that naturally expands to other pattern positions. I found that less > aesthetically pleasing, though, and so a context-sensitive keyword seemed > like the way to go. > > (For the record, though, I wouldn't describe `case _` as a special case of > `default`. They do exactly the same thing, and `_` is a useful pattern in > other contexts, so if anything the current `default` should be thought of > as syntactic sugar for `case _`.) > > > Can case _ be mixed with unknown case? How can we match all compile time > known cases but exclude future cases? > What’s your use case for that? That eliminates the possibility of “unknown case” giving you compile-time warnings for subsequently added cases, which was the entire purpose of adding the syntax in the first place. Should be something like `case *` that would capture all currently known > cases during compile time? case * and case _ would be the same in > exhaustive enums. > > > > I'll add these points to the "Alternatives Considered" section in the PR > later today. > > Jordan > > > On Jan 3, 2018, at 22:56, Xiaodi Wu <xiaodi...@gmail.com> wrote: > > As has already been said, “case unknown” is source-breaking because it > conflicts with any real cases named “unknown”; “\unknown” looks like a key > path but isn’t, and I wonder if it would potentially conflict with existing > key paths. > > In any case, my point was not to bikeshed the “unknown” part, but to ask > whether any consideration had been made to have the feature presented as a > flavor of default instead of a flavor of case. > > On Wed, Jan 3, 2018 at 23:57 Cheyo Jimenez <ch...@masters3d.com> wrote: > >> >> >> On Jan 3, 2018, at 6:52 PM, Xiaodi Wu via swift-evolution < >> swift-evolution@swift.org> wrote: >> >> This is a very nice revision. One bikeshedding thought: >> >> Since "unknown case" is presented as a special kind of "default", can't >> be mixed with "default", and can't be used in case patterns, why not >> "default unknown" (or "unknown default") instead of "unknown case"? >> >> >> `case _ :` is already a special case of default. >> I’d rather have `case unknown :` >> `unknown case :` is weird because of the order of `case`. >> >> Another alternative is `case \unknown :` >> `\unknown` would also allow pattern matching. >> >> >> >> >> >> On Wed, Jan 3, 2018 at 8:05 PM, Jordan Rose via swift-evolution < >> swift-evolution@swift.org> wrote: >> >>> On Jan 2, 2018, at 18:07, Jordan Rose <jordan_r...@apple.com> wrote: >>> >>> [Proposal: >>> https://github.com/apple/swift-evolution/blob/master/proposals/0192-non-exhaustive-enums.md >>> ] >>> >>> Whew! Thanks for your feedback, everyone. On the lighter side of >>> feedback—naming things—it seems that most people seem to like '*@frozen*', >>> and that does in fact have the connotations we want it to have. I like it >>> too. >>> >>> More seriously, this discussion has convinced me that it's worth >>> including what the proposal discusses as a *'future' case*. The key >>> point that swayed me is that this can produce a *warning* when the >>> switch is missing a case rather than an *error,* which both provides >>> the necessary compiler feedback to update your code and allows your >>> dependencies to continue compiling when you update to a newer SDK. I know >>> people on both sides won't be 100% satisfied with this, but does it seem >>> like a reasonable compromise? >>> >>> The next question is how to spell it. I'm leaning towards `unexpected >>> case:`, which (a) is backwards-compatible, and (b) also handles "private >>> cases", either the fake kind that you can do in C (as described in the >>> proposal), or some real feature we might add to Swift some day. `unknown >>> case:` isn't bad either. >>> >>> I too would like to just do `unknown:` or `unexpected:` but that's >>> technically a source-breaking change: >>> >>> switch foo { >>> case bar: >>> unknown: >>> while baz() { >>> while garply() { >>> if quux() { >>> break unknown >>> } >>> } >>> } >>> } >>> >>> >>> Another downside of the `unexpected case:` spelling is that it doesn't >>> work as part of a larger pattern. I don't have a good answer for that one, >>> but perhaps it's acceptable for now. >>> >>> I'll write up a revision of the proposal soon and make sure the core >>> team gets my recommendation when they discuss the results of the review. >>> >>> --- >>> >>> I'll respond to a few of the more intricate discussions tomorrow, >>> including the syntax of putting a new declaration inside the enum rather >>> than outside. Thank you again, everyone, and happy new year! >>> >>> >>> I ended up doing these in the opposite order, writing up the new >>> proposal first and not yet responding to the discussion that's further out. >>> You can read my revisions at >>> https://github.com/apple/swift-evolution/pull/777. >>> >>> In particular, I want to at least address: >>> - Dave D and Drew C's points about versioned libraries / linking >>> semantics of modules. >>> - Jason M's point about migration >>> and I'll do one more pass over the thread to see if there's anything >>> else I didn't address directly. (That doesn't mean everyone who disagrees, >>> just messages where I think there's more I can do to explain why the >>> proposal is the way it is.) >>> >>> Jordan >>> >>> P.S. Enjoying the Disney references. Thanks, Nevin and Dave. :-) >>> >>> _______________________________________________ >>> swift-evolution mailing list >>> swift-evolution@swift.org >>> https://lists.swift.org/mailman/listinfo/swift-evolution >>> >>> >> _______________________________________________ >> swift-evolution mailing list >> swift-evolution@swift.org >> https://lists.swift.org/mailman/listinfo/swift-evolution >> >> >
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