<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=""><br class=""><div><blockquote type="cite" class=""><div class="">On Feb 7, 2017, at 1:21 PM, Tanner Nelson <<a href="mailto:tanner@qutheory.io" class="">tanner@qutheory.io</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="content-type" content="text/html; charset=utf-8" class=""><div dir="auto" class=""><div class="">That's awesome. It looks like `<span style="background-color: rgba(255, 255, 255, 0);" class="">(planned) Open and closed enums` is exactly what I'm looking for. </span></div><div class=""><br class=""></div><div class="">Would it help if I created a concrete proposal for that or is it something the Swift team already has brewing?</div><div class=""><br class=""></div></div></div></blockquote><div><br class=""></div><div>Note that open enums also have to solve ABI stability across versions.</div><div><br class=""></div><div>Basically, it sounds like you have an enum for which there is a reasonable default handling in client code for any cases added in future versions of your framework. Note that this is not true of all enums. The current behavior of breaking clients when new cases are added forces them to think about this new variant and their assumptions associated therein. This is very desirable for many enums, even public ones.</div><div><br class=""></div><div>An intermediary approach could be to come up with an attribute to convey your intent ala <a href="https://github.com/apple/swift-evolution/blob/master/proposals/0047-nonvoid-warn.md" class="">https://github.com/apple/swift-evolution/blob/master/proposals/0047-nonvoid-warn.md</a>. The idea is to keep default behavior the same, but have something like (straw man syntax) @defaultCaseRequired.</div><div><br class=""></div><div><br class=""></div><blockquote type="cite" class=""><div class=""><div dir="auto" class=""><div class="">Sent from my iPhone</div><div class=""><br class="">On Feb 7, 2017, at 22:01, Michael Ilseman <<a href="mailto:milseman@apple.com" class="">milseman@apple.com</a>> wrote:<br class=""><br class=""></div><blockquote type="cite" class=""><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div class="">BTW, this will likely be part of the eventual design of “open”/resilient enums ala <a href="https://github.com/apple/swift/blob/master/docs/LibraryEvolution.rst#enums" class="">https://github.com/apple/swift/blob/master/docs/LibraryEvolution.rst#enums</a>. There, the goal is to reduce both ABI and source breakage caused by this sort of thing. It seems like for your purposes, you’re less inclined to care about ABI breakage than source breakage, though that may change in the future.</div><div class=""><br class=""></div><div class=""><br class=""></div><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Feb 7, 2017, at 7:12 AM, Tanner Nelson 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 dir="ltr" class="">Hello Swift Evolution,<div class=""><br class=""></div><div class="">I'd like to propose that a warning be emitted when default cases are omitted for enums from other modules. </div><div class=""><br class=""></div><div class="">What this would look like:</div><div class=""><br class=""></div><div class="">OtherModule:</div><div class="">```</div><div class="">public enum SomeEnum {</div><div class=""> case one</div><div class=""> case two</div><div class="">}</div><div class=""><br class=""></div><div class="">public let global: SomeEnum = .one</div><div class="">```</div><div class=""><br class=""></div><div class="">executable:</div><div class="">```</div><div class="">import OtherModule</div><div class=""><br class=""></div><div class="">switch OtherModule.global {</div><div class=""> case .one: break</div><div class=""> case .two: break</div><div class=""> ^~~~~ ⚠︎ Warning: Default case recommended for imported enums. Fix-it: Add `default: break`</div><div class="">}</div><div class="">```</div><div class=""><br class=""></div><div class="">Why:</div><div class=""><br class=""></div><div class="">Allowing the omission of a default case in an exhaustive switch makes the addition of a new case to the enum a breaking change. </div><div class="">In other words, if you're exhaustively switching on an enum from an imported library, the imported library can break your code by adding a new case to that enum (which the library authors may erroneously view as an additive/minor-bump change).</div><div class=""><br class=""></div><div class="">Background:</div><div class=""><br class=""></div><div class="">As a maintainer of a Swift framework, public enums have been a pain point in maintaining semver. They've made it difficult to implement additive features and have necessitated the avoidance of enums in our future public API plans.</div><div class=""><br class=""></div><div class="">Related Twitter thread: <a href="https://twitter.com/tanner0101/status/796860273760104454" class="">https://twitter.com/tanner0101/status/796860273760104454</a></div><div class=""><br class=""></div><div class="">Looking forward to hearing your thoughts.</div><div class=""><br class=""></div><div class="">Best,</div><div class="">Tanner</div><div class=""><br class=""></div><div class=""><div style="font-family:'sf ui text';font-size:12px" class=""><font color="#5f5f5f" class="">Tanner Nelson</font></div><div style="font-family:'sf ui text';font-size:12px" class=""><font color="#9dacd1" class="">Va</font><font color="#aeb2cf" class="">p</font><font color="#c8bacd" class="">o</font><font color="#d0becc" class="">r</font><font color="#9dacd1" class=""> </font></div><div style="font-family:'sf ui text';font-size:12px" class=""><font color="#676767" class="">+1 (435) 773-2831</font></div></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div></div>
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