<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div><br><br><div>Daniel Duan</div>Sent from my iPhone</div><div><br>On Jan 24, 2017, at 2:18 PM, Christopher Kornher via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html charset=utf-8"><meta http-equiv="Content-Type" content="text/html charset=utf-8"><div class="">I agree that this rule would be consistent with the handing of Swift function signatures, but my proposal is self-consistent and:</div><div class=""><br class=""></div><div class="">1) It is more powerful, matching on the case name or not as required.</div><div class="">2) Is consistent with existing switches that ignore associated values</div><div class="">3) Is constant with ignored labels in other Swift constructs (proposed and in past versions of Swift, at least)</div><div class="">4) Avoids a possible API change for current enums. This is currently legal but would not be if the enum case “name” is the entire signature for constructing it:</div><div class=""><br class=""></div><div class="">```</div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">enum</span><span style="font-variant-ligatures: no-common-ligatures" class=""> E {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> a( a: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Int</span><span style="font-variant-ligatures: no-common-ligatures" class=""> )</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> b( a: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Int</span><span style="font-variant-ligatures: no-common-ligatures" class=""> )</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo; min-height: 15px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> anEmum = </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">E</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">a</span><span style="font-variant-ligatures: no-common-ligatures" class="">( a: </span><span style="font-variant-ligatures: no-common-ligatures; color: #272ad8" class="">4</span><span style="font-variant-ligatures: no-common-ligatures" class=""> )</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo; min-height: 15px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo; min-height: 15px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo; color: rgb(186, 45, 162);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">switch</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">anEmum</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> .</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">a</span><span style="font-variant-ligatures: no-common-ligatures" class="">( let x ) :</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo; color: rgb(186, 45, 162);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">break</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> .</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">b</span><span style="font-variant-ligatures: no-common-ligatures" class="">( let x ) :</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo; color: rgb(186, 45, 162);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">break</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo; min-height: 15px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo; color: rgb(186, 45, 162);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">switch</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">anEmum</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> .</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">a</span><span style="font-variant-ligatures: no-common-ligatures" class="">( let y ) :</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo; color: rgb(186, 45, 162);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">break</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo; min-height: 15px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> .</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">b</span><span style="font-variant-ligatures: no-common-ligatures" class="">( let y ) :</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo; color: rgb(186, 45, 162);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">break</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Menlo;" class=""><span style="-webkit-text-stroke-width: initial; -webkit-text-stroke-color: rgb(0, 0, 0);" class="">```</span></div><div class="">So is this proposal worth creating a breaking change? I don’t think so. it would be possible to ignore the associated parameter name, but not the type, but that would further confuse case matching, I believe.</div><div class=""><br class=""></div><div class="">I personally don’t see much purpose in having two enum cases with the same name if they are always treated as distinct and there is no way to reason on the case name.</div></div></blockquote><div><br></div><div>Would you say the same for functions? Our opinions differ in what constitute a "name". In Swift, function names include parameters. Each enum case declares a function that creates a enum value. That's why it's *more* consistent for enum to have a similar definition of "name".</div><div><br></div><div>As for pattern matching, number of patterns the number of cases being matched have a many-to-one relationships. This is true in Swift and many </div><br><blockquote type="cite"><div><div class=""> If they are always distinct, then requiring different names eliminates unnecessary cognitive load. There is a good reason for functions to have the same “name” and different signatures, and there are precedents in many languages. </div><div class=""><br class=""></div><div class="">You may disagree, but I believe that enums exist to support reasoning on distinct cases and that muddying that by treating the associated value as part of the “signature" increases the language “surface area” while adding no tangible benefit.</div><div class=""><br class=""></div><br class=""><div><blockquote type="cite" class=""><div class="">On Jan 24, 2017, at 2:23 PM, Matthew Johnson 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 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=""><blockquote type="cite" class=""><div class=""><br class="Apple-interchange-newline">On Jan 24, 2017, at 3:10 PM, Christopher Kornher 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="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class="">Your example is only has only one case, which is not typical. Perhaps I am missing something, but the only reason that I can imagine for having a case with multiple ways to “construct” it is to have all variants of the case to match. If you don’t want them to match, use a different case name. </div></div></div></blockquote><div class=""><br class=""></div><div class="">It sounds like you are missing something. The `bar(a:)` and `bar(b:)` are the full case names. These are *not* the same case. The `bar` shorthand is allowed when there is no ambiguity, however for an enum with both `bar(a:)` and `bar(b:)` there *is* ambiguity and therefore the `bar` shorthand is not allowed. The programmer is required to spell out the full name of the case they wish to match.</div><div class=""><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><br class=""></div><div class="">It would still be possible to match on the different types of bar when needed:</div><div class=""><br class=""></div><div class="">```</div><div class="">enum Foo {<br class=""> case bar(a: Int)<br class=""> case bar(b: String)</div><div class=""> case notAbar<br class=""><div class="gmail_quote"><div dir="auto" class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg">}</div></div></div></div></div><div class=""><div class="gmail_quote"><div dir="auto" class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg"><br class=""></div></div></div></div></div><br class="Apple-interchange-newline"><div class=""> switch aFoo {</div><div class=""> case .bar( let a: Int) : // matches Ints only </div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>...</div><div class=""><br class=""> case .bar( let b: String) : // matches Strings only<br class=""> ...<br class=""><div class="gmail_quote"><div dir="auto" class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg">}</div><div class="gmail_msg"><br class=""></div><div class="gmail_msg"><div class="">switch aFoo {</div><div class=""> case .bar : // Matches both cases and that is a good thing</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>…</div><div class=""><br class=""></div><div class=""> case notAbar:</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>….</div><div class="">}<br class=""><div class="gmail_quote"><div dir="auto" class="gmail_msg"><div class="gmail_msg"><div class=""><br class=""></div></div></div></div></div></div><div class="gmail_msg">```</div><div class="gmail_msg"><br class=""></div></div></div></div></div><div class=""><blockquote type="cite" class=""><div class="">On Jan 24, 2017, at 5:27 AM, Xiaodi Wu 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="">I would imagine it would be logical to have it work just like it does now with functions. If case bar is distinct, then that should still work, but if bar is "overloaded," then case bar should be invalid for ambiguity. Seems fine to me, shouldn't break any existing code and therefore we don't lose anything.<br class=""><br class=""><br class=""><div class="gmail_quote"><div dir="ltr" class="">On Tue, Jan 24, 2017 at 01:13 David Hart via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex;"><div dir="auto" class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg"><br class="gmail_msg">On 24 Jan 2017, at 00:52, Joe Groff via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a>> wrote:<br class="gmail_msg"><br class="gmail_msg"></div><blockquote type="cite" class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg">We're not terribly principled about this right now with non-pattern declaration references. You can still reference an unapplied function by its base name alone without its labels, if it's unambiguous:</div><div class="gmail_msg"><br class="gmail_msg"></div><blockquote class="gmail_msg" style="margin: 0px 0px 0px 40px; border: none; padding: 0px;"><div class="gmail_msg">func foo(x: Int, y: Int) {}</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">let foo_x_y: (Int, Int) -> () = foo</div></blockquote><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">so it'd be consistent to continue to allow the same in pattern references.</div></div></blockquote><br class="gmail_msg"></div></div><div dir="auto" class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg">WRT ambiguity, do we loose the ability to pattern match on the naked case name when two cases share the same base name?</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">enum Foo {</div><div class="gmail_msg"> case bar(a: Int)</div><div class="gmail_msg"> case bar(b: String)</div><div class="gmail_msg">}</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">switch aFoo {</div><div class="gmail_msg"> case .bar: // matches both cases</div><div class="gmail_msg"> break</div><div class="gmail_msg">}</div></div></div>_______________________________________________<br class="gmail_msg">swift-evolution mailing list<br class="gmail_msg"><a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a><br class="gmail_msg"><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" class="gmail_msg" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class="gmail_msg"></blockquote></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></div></blockquote></div><br class=""></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></div></blockquote></div><br class="" style="font-family: Helvetica; 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