<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 class="">To what extend should pattern matching be used in "cases"?</div><div class=""><br class=""></div><div class="">Can there be value bindings? The current grammar says "pattern" which means:</div><div class=""><section class="section" style="padding: 15px 25px 30px;"><div class="syntax-defs" style="border-width: 0px 0px 0px 5px; border-left-style: solid; border-left-color: rgb(233, 233, 233); margin: 20px 0px; outline: 0px; padding: 0px 0px 0px 15px; vertical-align: baseline; line-height: 20.299999237060547px;"><div class="syntax-defs-group" style="border: 0px; margin: 0px 0px 12px; outline: 0px; padding: 0px; vertical-align: baseline;"><div style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" class=""><span class="syntax-def-name" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(128, 128, 128); font-style: italic;">pattern </span><span class="arrow" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 0px 0px 4px; vertical-align: baseline; color: rgb(128, 128, 128);">→ </span><span class="syntactic-cat" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 4px; vertical-align: baseline; font-style: italic; word-break: keep-all;"><a href="https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/wildcard-pattern" data-renderer-version="2" data-id="//apple_ref/swift/grammar/wildcard-pattern" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(0, 136, 204); text-decoration: none;" class="">wildcard-pattern</a></span><span class="optional" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"><span class="syntactic-cat" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 4px; vertical-align: baseline; font-style: italic; word-break: keep-all;"><a href="https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-annotation" data-renderer-version="2" data-id="//apple_ref/swift/grammar/type-annotation" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(0, 136, 204); text-decoration: none;" class="">type-annotation</a></span><sub class="subscript" style="border: 0px; margin: 0px 0px 0px -2px; outline: 0px; padding: 0px 4px 0px 0px; color: rgb(128, 128, 128); font-style: italic;">opt</sub></span></div><div style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" class=""><a name="//apple_ref/doc/uid/TP40014097-CH36-NoLink_627" style="border: 0px; margin: -85px 0px 0px; outline: 0px; padding: 85px 0px 0px; vertical-align: baseline; display: block; width: 0px; height: 0px; color: rgb(0, 136, 204);" class=""></a><span class="syntax-def-name" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(128, 128, 128); font-style: italic;">pattern </span><span class="arrow" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 0px 0px 4px; vertical-align: baseline; color: rgb(128, 128, 128);">→ </span><span class="syntactic-cat" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 4px; vertical-align: baseline; font-style: italic; word-break: keep-all;"><a href="https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/identifier-pattern" data-renderer-version="2" data-id="//apple_ref/swift/grammar/identifier-pattern" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(0, 136, 204); text-decoration: none;" class="">identifier-pattern</a></span><span class="optional" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"><span class="syntactic-cat" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 4px; vertical-align: baseline; font-style: italic; word-break: keep-all;"><a href="https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-annotation" data-renderer-version="2" data-id="//apple_ref/swift/grammar/type-annotation" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(0, 136, 204); text-decoration: none;" class="">type-annotation</a></span><sub class="subscript" style="border: 0px; margin: 0px 0px 0px -2px; outline: 0px; padding: 0px 4px 0px 0px; color: rgb(128, 128, 128); font-style: italic;">opt</sub></span></div><div style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" class=""><a name="//apple_ref/doc/uid/TP40014097-CH36-NoLink_628" style="border: 0px; margin: -85px 0px 0px; outline: 0px; padding: 85px 0px 0px; vertical-align: baseline; display: block; width: 0px; height: 0px; color: rgb(0, 136, 204);" class=""></a><span class="syntax-def-name" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(128, 128, 128); font-style: italic;">pattern </span><span class="arrow" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 0px 0px 4px; vertical-align: baseline; color: rgb(128, 128, 128);">→ </span><span class="syntactic-cat" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 4px; vertical-align: baseline; font-style: italic; word-break: keep-all;"><a href="https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/value-binding-pattern" data-renderer-version="2" data-id="//apple_ref/swift/grammar/value-binding-pattern" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(0, 136, 204); text-decoration: none;" class="">value-binding-pattern</a></span></div><div style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" class=""><a name="//apple_ref/doc/uid/TP40014097-CH36-NoLink_629" style="border: 0px; margin: -85px 0px 0px; outline: 0px; padding: 85px 0px 0px; vertical-align: baseline; display: block; width: 0px; height: 0px; color: rgb(0, 136, 204);" class=""></a><span class="syntax-def-name" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(128, 128, 128); font-style: italic;">pattern </span><span class="arrow" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 0px 0px 4px; vertical-align: baseline; color: rgb(128, 128, 128);">→ </span><span class="syntactic-cat" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 4px; vertical-align: baseline; font-style: italic; word-break: keep-all;"><a href="https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/tuple-pattern" data-renderer-version="2" data-id="//apple_ref/swift/grammar/tuple-pattern" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(0, 136, 204); text-decoration: none;" class="">tuple-pattern</a></span><span class="optional" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"><span class="syntactic-cat" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 4px; vertical-align: baseline; font-style: italic; word-break: keep-all;"><a href="https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-annotation" data-renderer-version="2" data-id="//apple_ref/swift/grammar/type-annotation" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(0, 136, 204); text-decoration: none;" class="">type-annotation</a></span><sub class="subscript" style="border: 0px; margin: 0px 0px 0px -2px; outline: 0px; padding: 0px 4px 0px 0px; color: rgb(128, 128, 128); font-style: italic;">opt</sub></span></div><div style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" class=""><a name="//apple_ref/doc/uid/TP40014097-CH36-NoLink_630" style="border: 0px; margin: -85px 0px 0px; outline: 0px; padding: 85px 0px 0px; vertical-align: baseline; display: block; width: 0px; height: 0px; color: rgb(0, 136, 204);" class=""></a><span class="syntax-def-name" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(128, 128, 128); font-style: italic;">pattern </span><span class="arrow" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 0px 0px 4px; vertical-align: baseline; color: rgb(128, 128, 128);">→ </span><span class="syntactic-cat" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 4px; vertical-align: baseline; font-style: italic; word-break: keep-all;"><a href="https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/enum-case-pattern" data-renderer-version="2" data-id="//apple_ref/swift/grammar/enum-case-pattern" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(0, 136, 204); text-decoration: none;" class="">enum-case-pattern</a></span></div><div style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" class=""><a name="//apple_ref/doc/uid/TP40014097-CH36-NoLink_631" style="border: 0px; margin: -85px 0px 0px; outline: 0px; padding: 85px 0px 0px; vertical-align: baseline; display: block; width: 0px; height: 0px; color: rgb(0, 136, 204);" class=""></a><span class="syntax-def-name" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(128, 128, 128); font-style: italic;">pattern </span><span class="arrow" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 0px 0px 4px; vertical-align: baseline; color: rgb(128, 128, 128);">→ </span><span class="syntactic-cat" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 4px; vertical-align: baseline; font-style: italic; word-break: keep-all;"><a href="https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/optional-pattern" data-renderer-version="2" data-id="//apple_ref/swift/grammar/optional-pattern" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(0, 136, 204); text-decoration: none;" class="">optional-pattern</a></span></div><div style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" class=""><a name="//apple_ref/doc/uid/TP40014097-CH36-NoLink_632" style="border: 0px; margin: -85px 0px 0px; outline: 0px; padding: 85px 0px 0px; vertical-align: baseline; display: block; width: 0px; height: 0px; color: rgb(0, 136, 204);" class=""></a><span class="syntax-def-name" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(128, 128, 128); font-style: italic;">pattern </span><span class="arrow" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 0px 0px 4px; vertical-align: baseline; color: rgb(128, 128, 128);">→ </span><span class="syntactic-cat" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 4px; vertical-align: baseline; font-style: italic; word-break: keep-all;"><a href="https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/type-casting-pattern" data-renderer-version="2" data-id="//apple_ref/swift/grammar/type-casting-pattern" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(0, 136, 204); text-decoration: none;" class="">type-casting-pattern</a></span></div><div style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" class=""><a name="//apple_ref/doc/uid/TP40014097-CH36-NoLink_633" style="border: 0px; margin: -85px 0px 0px; outline: 0px; padding: 85px 0px 0px; vertical-align: baseline; display: block; width: 0px; height: 0px; color: rgb(0, 136, 204);" class=""></a><span class="syntax-def-name" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(128, 128, 128); font-style: italic;">pattern </span><span class="arrow" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 0px 0px 4px; vertical-align: baseline; color: rgb(128, 128, 128);">→ </span><span class="syntactic-cat" style="border: 0px; margin: 0px; outline: 0px; padding: 0px 4px; vertical-align: baseline; font-style: italic; word-break: keep-all;"><a href="https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/expression-pattern" data-renderer-version="2" data-id="//apple_ref/swift/grammar/expression-pattern" style="border: 0px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; color: rgb(0, 136, 204); text-decoration: none;" class="">expression-pattern</a></span></div></div></div></section><section class="section" style="padding: 15px 25px 30px;"><a name="//apple_ref/doc/uid/TP40014097-CH36-ID420" style="border: 0px; font-size: 10px; margin: -85px 0px 0px; outline: 0px; padding: 85px 0px 0px; vertical-align: baseline; display: block; width: 0px; height: 0px; color: rgb(0, 136, 204); font-family: Helvetica, Arial, sans-serif;" class=""></a></section></div><br class=""><div><blockquote type="cite" class=""><div class="">Am 04.02.2016 um 19:35 schrieb Craig Cruden <<a href="mailto:ccruden@novafore.com" class="">ccruden@novafore.com</a>>:</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="">cases was added instead of using `cases` because of the potential problems foreseen where the parser would have trouble identifying a list of values. <div class=""><br class=""></div><div class="">cases would be restricted to key: value, key: value, key: value and would be considered syntactic sugar that would expand out to </div><div class=""> case key1: value1</div><div class=""> case key2: value2</div><div class=""> case key3: value3 </div><div class="">as far as the compilation was concerned.</div><div class=""><br class=""></div><div class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On 2016-02-05, at 1:31:09, Maximilian Hünenberger 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="">I definitely see the point against dictionaries but I’m afraid of the actual pattern matching in "cases".</div><div class=""><br class=""></div><div class="">match(1) {</div><div class=""> case 1, 3: 10</div><div class=""> case 2, 4: 20</div><div class=""> default: 30</div><div class="">}</div><div class=""><br class=""></div><div class="">// with "cases"</div><div class=""><br class=""></div><div class=""><div class="">match(1) { cases</div><div class=""> 1, 3: 10,</div><div class=""> 2, 4: 20,</div><div class=""> default: 30</div><div class="">}</div></div><div class=""><br class=""></div><div class="">// it is very hard to disambiguate between pattern and return value even though for the compiler it could be doable</div><div class=""><div class="">match(1) { cases</div><div class=""> 1, 3: 10, 2, 4: 20, default: 30</div><div class="">}</div></div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">There should be a more visible distinction between two "<span style="color: rgb(51, 51, 51); background-color: rgb(255, 255, 255);" class="">case-item-map" <b class=""><u class="">like</u></b> "|". But we have to consider "expression-patterns" where operators (like "|") are ambiguous.</span></div><div class=""><span style="color: rgb(51, 51, 51); background-color: rgb(255, 255, 255);" class=""><br class=""></span></div><div class=""><span style="background-color: rgb(255, 255, 255);" class=""><font color="#333333" class="">- Maximilian</font></span></div><br class=""><div class=""><blockquote type="cite" class=""><div class="">Am 04.02.2016 um 18:48 schrieb Paul Ossenbruggen <<a href="mailto:possen@gmail.com" class="">possen@gmail.com</a>>:</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 is a good point and I forgot about that. There are frequent cases where what I am dealing with is not hashable and it is generally a lot of work to make it hashable, including adding a heading function which if done wrong, can lead to errors. <br class=""><br class="">Sent from my iPhone</div><div class=""><br class="">On Feb 4, 2016, at 8:38 AM, Charles Constant via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""></div><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class="">I still vote for keeping "cases"</div><br class=""><div class="gmail_extra"><div class="gmail_quote"><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 style="word-wrap:break-word" class=""><div class="">I see it as a replacement for dictionary literal "pattern matching":<br class=""></div><div class=""><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(209,47,27)" class=""><span style="" class="">[</span><span style="color:rgb(39,42,216)" class="">1</span><span style="" class=""> : </span>"one"<span style="" class="">, </span><span style="color:rgb(39,42,216)" class="">2</span><span style="" class=""> : </span>"two"<span style="" class="">, </span><span style="color:rgb(39,42,216)" class="">3</span><span style="" class=""> : </span>"three"<span style="" class="">][</span><span style="color:rgb(39,42,216)" class="">1</span><span style="" class="">] ?? </span>"undefined"</div></div><div class=""></div></div></blockquote><div class=""><br class=""></div><div class="">A dictionary needs keys that are Hashable. A dictionary produces an optional. We've discussed this, and more, earlier in the thread.</div><div class=""><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 style="word-wrap:break-word" class=""><div class="">Even though it would be nice to have but I don’t think that I would use it frequently.</div></div></blockquote><div class=""><br class=""></div><div class="">Granted, it's a bit ugly, but given the choice, I would pick "cases" over "case case case case ..." every time.</div><div class=""><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 style="word-wrap:break-word" class=""><div class="">In addition, to be more consistent with "case", "cases" would introduce pattern matching which doesn’t seem right with this concise syntax.</div></div></blockquote><div class=""><br class=""></div><div class="">I haven't thought this through. It just bums me out a little to replace the switch with something that still has imho unnecessary verbosity.</div><div class=""><br class=""></div><div class=""><br class=""></div></div></div></div>
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