On Thu, Jan 4, 2018 at 19:29 Cheyo J. Jimenez <ch...@masters3d.com> wrote:
> On Jan 4, 2018, at 3:50 PM, Xiaodi Wu <xiaodi...@gmail.com> wrote: > > > On Thu, Jan 4, 2018 at 18:39 Cheyo J. Jimenez <ch...@masters3d.com> wrote: > >> >> On Jan 4, 2018, at 2:55 PM, Xiaodi Wu <xiaodi...@gmail.com> wrote: >> >> >> On Thu, Jan 4, 2018 at 17:15 Cheyo J. Jimenez <ch...@masters3d.com> >> wrote: >> >>> On Jan 4, 2018, at 11:53 AM, Xiaodi Wu <xiaodi...@gmail.com> wrote: >>> >>> >>> 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. >>> >>> >>> I was thinking of a generalized `unknown case` pattern but that is out >>> of scope for this proposal. >>> <https://github.com/apple/swift-evolution/pull/777/files#diff-a68dc745ee86d09566b232b6954c5158R321> >>> >>> >>> switch excuse { >>> case .eatenByPet : >>> //… >>> unknown case: >>> // … >>> case _: >>> // … >>> } >>> >>> >>> Should there be something like `case *` that would capture all currently >>>> known cases during compile time? case * and case _ would be the same in >>>> exhaustive enums. >>>> >>> >>> This is why I was suggesting another pattern that only captures known >>> cases at compile time: >>> >>> switch excuse { >>> case .eatenByPet : >>> //… >>> case * : // All cases captured at compile time. >>> // … >>> unknown case: >>> // … >>> } >>> >> >> Sorry, I don’t understand. However you spell it, what is your use case >> for this? The stated purpose of “unknown case” is to gain compile-time >> exhaustiveness testing, but this would not allow for that. >> >> >> >> >> >> switch (excuse, notifiedTeacherBeforeDeadline) {case (.eatenByPet, true): >> // …case (.thoughtItWasDueNextWeek, true): >> // …case (unknown case, true): >> // …case (_, false): >> // …} >> >> >> Im referring to the future direction section in the new PR >> <https://github.com/jrose-apple/swift-evolution/blob/6061c01fb4a6d742ba7213f46979c9b82891fc14/proposals/0192-non-exhaustive-enums.md#future-directions>. >> The above example if from there. >> >> I am fine with `unknown case` being required to be at the end of the >> switch for now. >> >> I think of `unknown case` as a pattern that only matches unknown cases no >> matter where on the switch it is. >> >> This is why I do not think that `default unknown` would work well once >> `unknown case` can be used a pattern. >> >> We can start a new thread on this if you’d like. >> > > The reason I put forward “default unknown” is precisely because the > proposed feature *cannot* be used in a pattern and therefore seems more apt > as not a case. > > It can not be used in a pattern now but you could in the future if left as > `case`. > > > It actually makes it more natural to use in the given example above > because “default unknown” could actually be used to provide compile-time > exhaustiveness checking for such a tuple pattern, whereas without being > able to use “unknown case” in a pattern you can’t write “case (unknown > case, _)”. > > > The way `unknown case` enforces compile-time exhaustiveness is by only > matching unknown cases. The implementation may be more close to default by > the virtue of being forced to go at the end of the switch statement now but > that should not dictate the user experience. > We seem to agree that, by virtue of not supporting use in a pattern and being placed at the end, the feature is a flavor of default. I’m still not sure I understand why you believe it should not be a flavor of default going forward. > You still haven’t answered my question, though—what’s the use case for the > feature you propose? > > > My use case would be distinguishing between compile time known cases vs > “future only” cases (or unknown cases). > I understand that the feature you propose would allow you to make such a distinction, but again, what is your use case for doing so? This depends on generalized `unknown case` patterns which is out of scope. > I am happy to talk more about this on a different thread when this proposal > gets approved. > > > > > >> >> >> >> >> >>> >>>> >>>> >>>> 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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