<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 8, 2017, at 1:34 AM, Tino Heth 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=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><br class=""><blockquote type="cite" class=""><div class=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" 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></blockquote></div>Depending on the context, even with a default the change might be breaking — but without giving notice to the framework client!<div class="">Additionally, it would feel very strange for me to have a default clause for bool-like enums* or other examples where there can't be any additional cases.</div><div class=""><br class=""></div><div class="">When there are two types of enums, the proposal makes sense for the "open"-ones; but I'm not sure if I like the concept of having two kinds of enum.</div></div></div></blockquote><div><br class=""></div>Why not? Bool-like enums would be declared ‘closed’, and would not require a default case (but adding a new case would then break ABI).</div><div><br class=""></div><div>For better or worse we need the ability to define enums that admit new cases without breaking ABI. Whether or not this is the default for all enums, or enabled with a special attribute can be designed later when we send out evolution proposals for resilience-related features.</div><div><br class=""></div><div>Slava</div><div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><br class=""></div><div class="">- Tino</div><div class=""><br class=""></div><div class="">* tiny anecdote: I actually have seen the equivalent of this</div><div class=""><br class=""></div><div class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> reallyExhaustive(input: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Bool</span><span style="font-variant-ligatures: no-common-ligatures" class="">) {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">if</span><span style="font-variant-ligatures: no-common-ligatures" class=""> input </span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">==</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">true</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(209, 47, 27);" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">print</span><span style="font-variant-ligatures: no-common-ligatures;" class="">(</span><span style="font-variant-ligatures: no-common-ligatures" class="">"true"</span><span style="font-variant-ligatures: no-common-ligatures;" class="">)</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>} </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">else</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">if</span><span style="font-variant-ligatures: no-common-ligatures" class=""> input != </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">true</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(209, 47, 27);" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">print</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> (</span><span style="font-variant-ligatures: no-common-ligatures" class="">"not true"</span><span style="font-variant-ligatures: no-common-ligatures;" class="">)</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>} </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">else</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(209, 47, 27);" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><span class="Apple-tab-span" style="white-space:pre"> </span></span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">print</span><span style="font-variant-ligatures: no-common-ligatures;" class="">(</span><span style="font-variant-ligatures: no-common-ligatures" class="">"just to be save"</span><span style="font-variant-ligatures: no-common-ligatures;" class="">)</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>}</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div class="">in the wild… but I don't remember the comment I wrote ;-)</div></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class="">https://lists.swift.org/mailman/listinfo/swift-evolution<br class=""></div></blockquote></div><br class=""></body></html>