<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div><blockquote type="cite" class=""><div class="">On Aug 8, 2017, at 3:28 PM, Jordan Rose via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">Let's now flip this to the other side of the equation. I've been talking about us disallowing exhaustive switching, i.e. "if the enum might grow new cases you must have a 'default' in a switch". In previous (in-person) discussions about this feature, it's been pointed out that the code in an otherwise-fully-covered switch is, by definition, unreachable, and therefore untestable. This also isn't a desirable situation to be in, but it's mitigated somewhat by the fact that there probably aren't many framework enums you should exhaustively switch over anyway. (Think about Apple's frameworks again.) I don't have a great answer, though.<br class=""><br class="">For people who like exhaustive switches, we thought about adding a new kind of 'default'—let's call it 'unknownCase' just to be able to talk about it. This lets you get warnings when you update to a new SDK, but is even more likely to be untested code. We didn't think this was worth the complexity.<br class=""></div></div></blockquote><br class=""></div><div>A question: Does it make sense to switch on a non-exhuastive enum at all? Maybe, from the public vantage point, a closed enum should be indistinguishable from a struct with static properties/methods—if you can switch over one, it's only through its conformance to `Equatable` or its implementation of a public `~=` operator.</div><div><br class=""></div><div>(IIRC, we ended up somewhere quite similar to this with our "import Objective-C string constants as enums" feature—it actually ends up creating structs instead.)</div><br class=""><div class="">
<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div class=""><div style="font-size: 12px; " class="">-- </div><div style="font-size: 12px; " class="">Brent Royal-Gordon</div><div style="font-size: 12px; " class="">Architechies</div></div></span>
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