<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div></div><div><br></div><div><br>On Jan 4, 2018, at 10:49 AM, Jordan Rose <<a href="mailto:jordan_rose@apple.com">jordan_rose@apple.com</a>> wrote:<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html; charset=utf-8">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.<div class=""><br class=""></div><div class="">To Cheyo's point, if this <i class="">were</i> 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.</div><div class=""><br class=""></div><div class="">(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 _`.)</div></div></blockquote><div><br></div><div>Can case _ be mixed with unknown case? How can we match all compile time known cases but exclude future cases? 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. </div><div><br></div><div><br></div><blockquote type="cite"><div><div class=""><br class=""></div><div class="">I'll add these points to the "Alternatives Considered" section in the PR later today.</div><div class=""><br class=""></div><div class="">Jordan<br class=""><div class=""><br class=""><div class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Jan 3, 2018, at 22:56, Xiaodi Wu <<a href="mailto:xiaodi.wu@gmail.com" class="">xiaodi.wu@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">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.<br class=""><br class="">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.<br class=""><br class=""><div class="gmail_quote"><div dir="ltr" class="">On Wed, Jan 3, 2018 at 23:57 Cheyo Jimenez <<a href="mailto:cheyo@masters3d.com" class="">cheyo@masters3d.com</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="auto" class=""><div class=""></div><div class=""><br class=""></div><div class=""><br class="">On Jan 3, 2018, at 6:52 PM, Xiaodi Wu via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""></div><blockquote type="cite" class=""><div class=""><div dir="ltr" class="">This is a very nice revision. One bikeshedding thought:<div class=""><br class=""></div><div class="">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"?</div></div></div></blockquote><div class=""><br class=""></div></div><div dir="auto" class="">`case _ :` is already a special case of default. <div class="">I’d rather have `case unknown :`</div><div class="">`unknown case :` is weird because of the order of `case`. </div><div class=""><br class=""></div><div class="">Another alternative is `case \unknown :`</div><div class="">`\unknown` would also allow pattern matching. </div></div><div dir="auto" class=""><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class=""><br class=""></div><div class="gmail_extra"><br class=""><div class="gmail_quote">On Wed, Jan 3, 2018 at 8:05 PM, Jordan Rose via swift-evolution <span dir="ltr" class=""><<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word;line-break:after-white-space" class=""><span class=""><div class=""><blockquote type="cite" class=""><div class="">On Jan 2, 2018, at 18:07, Jordan Rose <<a href="mailto:jordan_rose@apple.com" target="_blank" class="">jordan_rose@apple.com</a>> wrote:</div><br class="m_3038813019960738014m_4426090214486360640Apple-interchange-newline"><div class=""><div style="word-wrap:break-word;line-break:after-white-space" class=""><div class="">[Proposal: <a href="https://github.com/apple/swift-evolution/blob/master/proposals/0192-non-exhaustive-enums.md" style="font-family:Helvetica,arial,sans-serif" target="_blank" class="">https://github.com/apple/swift-evolution/blob/master/proposals/0192-non-exhaustive-enums.md</a>]</div><div class=""><br class=""></div><div class="">Whew! Thanks for your feedback, everyone. On the lighter side of feedback—naming things—it seems that most people seem to like '<b class="">@frozen</b>', and that does in fact have the connotations we want it to have. I like it too.</div><div class=""><br class=""></div><div class="">More seriously, this discussion has convinced me that it's worth including what the proposal discusses as a <b class="">'future' case</b>. The key point that swayed me is that this can produce a <i class="">warning</i> when the switch is missing a case rather than an <i class="">error,</i> 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?</div><div class=""><br class=""></div><div class="">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.</div><div class=""><br class=""></div><div class="">I too would like to just do `unknown:` or `unexpected:` but that's technically a source-breaking change:</div><div class=""><br class=""></div><blockquote style="margin:0 0 0 40px;border:none;padding:0px" class=""><div class="">switch foo {</div><div class="">case bar:</div><div class=""> unknown:</div><div class=""> while baz() {</div><div class=""> while garply() {</div><div class=""> if quux() {</div><div class=""> break unknown</div><div class=""> }</div><div class=""> }</div><div class=""> }</div><div class="">}</div></blockquote><div class=""><br class=""></div><div class="">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.</div><div class=""><br class=""></div><div class="">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.</div><div class=""><br class=""></div><div class="">---</div><div class=""><br class=""></div><div class=""><div class="">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!</div></div></div></div></blockquote><br class=""></div></span><div class="">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 <a href="https://github.com/apple/swift-evolution/pull/777" target="_blank" class="">https://github.com/apple/swift-evolution/pull/777</a>.</div><div class=""><br class=""></div><div class="">In particular, I want to at least address:</div><div class="">- Dave D and Drew C's points about versioned libraries / linking semantics of modules.</div><div class="">- Jason M's point about migration</div>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.)<div class=""><br class=""></div><div class="">Jordan</div><div class=""><br class=""></div><div class="">P.S. Enjoying the Disney references. Thanks, Nevin and Dave. :-)</div></div><br class="">_______________________________________________<br class="">
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