<div dir="ltr">I just realized something we can already do *now* (albeit with a lot of boilerplate) that looks really sleek at the point of use. For example:<div><br></div><div><div><font face="monospace, monospace">let json = JSON.number(4)</font></div><div><font face="monospace, monospace"><br></font></div><div><font face="monospace, monospace">if let n = json.number {</font></div><div><font face="monospace, monospace"> // n is a Double here</font></div><div><font face="monospace, monospace">}</font></div></div><div><font face="monospace, monospace"><br></font></div><div><font face="monospace, monospace">guard let s = json.string else {</font></div><div><font face="monospace, monospace"> return</font></div><div><font face="monospace, monospace">}</font></div><div><br></div><div>Making this work is actually quite straightforward, and simply requires extending the enum with a property for each unwrappable case, which returns an Optional of the associated value or nil if it is a different case.</div><div><br></div><div>If we had a way to eliminate the boilerplate, such as an “@unwrappable” attribute or a magic “Unwrappable” protocol that would cause the complier to generate the requisite properties, then it might entirely obviate the need for an “unwrap” keyword, or any change to pattern matching at all.</div><div><br></div><div>Here is what it takes to make your JSON enum behave as I describe:</div><div><br></div><div><div><font face="monospace, monospace">extension JSON {</font></div><div><font face="monospace, monospace"> var string: String? {</font></div><div><font face="monospace, monospace"> if case let .string(x) = self { return x }</font></div><div><font face="monospace, monospace"> return nil</font></div><div><font face="monospace, monospace"> }</font></div><div><font face="monospace, monospace"> </font></div><div><font face="monospace, monospace"> var number: Double? {</font></div><div><font face="monospace, monospace"> if case let .number(x) = self { return x }</font></div><div><font face="monospace, monospace"> return nil</font></div><div><font face="monospace, monospace"> }</font></div><div><font face="monospace, monospace"> </font></div><div><font face="monospace, monospace"> var boolean: Bool? {</font></div><div><font face="monospace, monospace"> if case let .boolean(x) = self { return x }</font></div><div><font face="monospace, monospace"> return nil</font></div><div><font face="monospace, monospace"> }</font></div><div><font face="monospace, monospace"> </font></div><div><font face="monospace, monospace"> var array: [JSON]? {</font></div><div><font face="monospace, monospace"> if case let .array(x) = self { return x }</font></div><div><font face="monospace, monospace"> return nil</font></div><div><font face="monospace, monospace"> }</font></div><div><font face="monospace, monospace"> </font></div><div><font face="monospace, monospace"> var dictionary: [String: JSON]? {</font></div><div><font face="monospace, monospace"> if case let .dictionary(x) = self { return x }</font></div><div><font face="monospace, monospace"> return nil</font></div><div><font face="monospace, monospace"> }</font></div><div><font face="monospace, monospace">}</font></div></div><div><div><br></div><div>With compiler support this could probably avoid creating the intermediate Optional altogether.</div><div><br></div><div>Nevin</div><div><br></div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Nov 1, 2016 at 4:28 PM, Nevin Brackett-Rozinsky <span dir="ltr"><<a href="mailto:nevin.brackettrozinsky@gmail.com" target="_blank">nevin.brackettrozinsky@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Bikeshedding here—is there any way we can make it look like this for enums?<div><br></div><div><font face="monospace, monospace">if let str = unwrap json.string {</font></div><div><font face="monospace, monospace"> // str is the value from the .string enum case</font></div><div><font face="monospace, monospace">}</font></div><div><br></div><div>Essentially, the “unwrap” keyword would treat the last “path component” of what follows as an enum case, and extract the associated value if it matches.</div><div><br></div><div>This could even work with tuple destructuring, as in:</div><div><br></div><div><div><font face="monospace, monospace">guard let (theCode, someMessage) = unwrap myResponse.contact else {</font></div><div><font face="monospace, monospace"> return</font></div><div><font face="monospace, monospace">}</font></div></div><div><br></div><div>And of course we could add a sugared form for optionals to allow the simple, “<font face="monospace, monospace">if unwrap x { … }</font>”.</div><div><br></div><div>I’m not sure if this is where we want to take the idea, it’s just something I thought of.</div><div><br></div><div>If we did go that route, then we might need to disallow enums from having properties with the same names as their cases (otherwise, eg. json.string would refer to a property not a case).</div><div><br></div><div>On the other hand, a slightly different syntax would avoid that issue entirely—for instance,</div><div><br></div><div><font face="monospace, monospace">if let str = unwrap json(.string) { … }</font></div><div>or</div><div><font face="monospace, monospace">if let str = unwrap</font><span style="font-family:monospace,monospace">(.string)</span><font face="monospace, monospace"> json { … }</font></div><div><br></div><div>That last one could even be sugared further when shadowing is desired:</div><div><br></div><div><div><font face="monospace, monospace">if unwrap</font><span style="font-family:monospace,monospace">(.string)</span><font face="monospace, monospace"> json {</font></div><div><font face="monospace, monospace"> // json is a String in here</font></div><div><font face="monospace, monospace">}</font></div></div><div><br></div><div>Potentially worthwhile?<span class="HOEnZb"><font color="#888888"><br></font></span></div><span class="HOEnZb"><font color="#888888"><div><br></div><div>Nevin</div><div><br></div></font></span><div class="gmail_extra"><br><div class="gmail_quote"><div><div class="h5">On Tue, Nov 1, 2016 at 2:42 PM, Erica Sadun via swift-evolution <span dir="ltr"><<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>></span> wrote:<br></div></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div><div class="h5"><div style="word-wrap:break-word">With massive revisions. I've added Xiaodi Wu to author list. I've combined all unwrapping together. I've added a much more sensible approach (plus a bluesky one) for real world enumerations.<div><br></div><div>Gist with live updates here: <a href="https://gist.github.com/erica/db9ce92b3d23cb20799460f603c0ae7c" target="_blank">https://gist.github.com/<wbr>erica/db9ce92b3d23cb20799460f6<wbr>03c0ae7c</a></div><div><br></div><div>Send feedback, I will continue to revise.</div><div><br></div><div>-- E</div><div><br></div><div><br></div><div><h1 style="box-sizing:border-box;margin:0px 0px 16px;line-height:1.25;padding-bottom:0.3em;border-bottom:1px solid rgb(238,238,238);color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";background-color:rgb(255,255,255)">Better Unwrapping</h1><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><li style="box-sizing:border-box">Proposal: TBD</li><li style="box-sizing:border-box;margin-top:0.25em">Author: <a href="https://github.com/erica" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">Erica Sadun</a>, <a href="https://github.com/lattner" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">Chris Lattner</a>, <a href="https://github.com/xwu" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">Xiaodi Wu</a> David Goodine</li><span class="m_-4659585067960143237gmail-"><li style="box-sizing:border-box;margin-top:0.25em">Status: TBD</li><li style="box-sizing:border-box;margin-top:0.25em">Review manager: TBD</li></span></ul><h2 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;line-height:1.25;padding-bottom:0.3em;border-bottom:1px solid rgb(238,238,238);color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";background-color:rgb(255,255,255)"><a id="m_-4659585067960143237gmail-m_7548809065351022967user-content-introduction" class="m_-4659585067960143237gmail-m_7548809065351022967anchor" href="https://gist.github.com/erica/db9ce92b3d23cb20799460f603c0ae7c#introduction" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Introduction</h2><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">This proposal redesigns common unwrapping tasks:</p><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><li style="box-sizing:border-box">It introduces the <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">unwrap</code> keyword for optional values</li><li style="box-sizing:border-box;margin-top:0.25em">It re-architects <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">guard case</code> and <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">if case</code> grammar to support unwrapping more complex enumerations by dropping the <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">case</code> keyword and replacing <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">=</code> with <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">~=</code>.</li><li style="box-sizing:border-box;margin-top:0.25em">It applies <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">unwrap</code> to non-optional values</li></ul><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">Swift Evolution threads:</p><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><span class="m_-4659585067960143237gmail-"><li style="box-sizing:border-box"><a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20161024/028440.html" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">guard let x = x</a></li></span><li style="box-sizing:border-box;margin-top:0.25em"><a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160201/thread.html" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">Using a <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">bind</code> keyword</a>.</li><li style="box-sizing:border-box;margin-top:0.25em"><a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20161024/tbd.html" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">Fixing pattern matching grammar</a></li></ul><h2 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;line-height:1.25;padding-bottom:0.3em;border-bottom:1px solid rgb(238,238,238);color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";background-color:rgb(255,255,255)"><a id="m_-4659585067960143237gmail-m_7548809065351022967user-content-motivation" class="m_-4659585067960143237gmail-m_7548809065351022967anchor" href="https://gist.github.com/erica/db9ce92b3d23cb20799460f603c0ae7c#motivation" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Motivation</h2><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">Unwrapping values is one of the most common Swift tasks and it is unnecessarily complex. This proposal simplifies this process and enhances code safety and readability.</p><h3 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;font-size:1.25em;line-height:1.25;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";background-color:rgb(255,255,255)"><a id="m_-4659585067960143237gmail-m_7548809065351022967user-content-optionals" class="m_-4659585067960143237gmail-m_7548809065351022967anchor" href="https://gist.github.com/erica/db9ce92b3d23cb20799460f603c0ae7c#optionals" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Optionals</h3><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">Swift lacks a safe way to bind an optional to a shadowed same-name variable in condition clauses like those used in <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">guard</code> and <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">if</code> statements.</p><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">Compare:</p><div class="m_-4659585067960143237gmail-m_7548809065351022967highlight m_-4659585067960143237gmail-m_7548809065351022967highlight-source-swift" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:0px;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-radius:3px;word-break:normal"><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> foo <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> foo <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// redundant</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">some</span>(foo) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> foo <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// overly complex</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> unwrap foo <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// simple</span></pre></div><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><li style="box-sizing:border-box">Using "foo = foo" fails <a href="https://en.wikipedia.org/wiki/Don%27t_repeat_yourself" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">DRY principles</a>. </li><li style="box-sizing:border-box;margin-top:0.25em">Using <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">case let .some(foo) = foo</code> or <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">case .some(let foo) = foo</code> fails <a href="https://en.wikipedia.org/wiki/KISS_principle" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">KISS principles</a></li></ul><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">unwrap</code> guarantees that an unwrapped shadow uses the same name as the wrapped version. This ensures that a conditionally-bound item cannot accidentally shadow another symbol. It eliminates repetition and retains clarity. Further, the <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">unwrap</code> keyword is common, simple to understand, and easy to search for if Swift users are unfamiliar with it.</p><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">In the rare case that the binding is variable, use the re-imagined <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">var ~=</code> syntax</p><h3 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;font-size:1.25em;line-height:1.25;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";background-color:rgb(255,255,255)"><a id="m_-4659585067960143237gmail-m_7548809065351022967user-content-general-enumerations" class="m_-4659585067960143237gmail-m_7548809065351022967anchor" href="https://gist.github.com/erica/db9ce92b3d23cb20799460f603c0ae7c#general-enumerations" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>General Enumerations</h3><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">Swift's <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">guard case</code> and <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">if case</code> statements stand out for their unintuitive approach. They look like assignment statements but they are <em style="box-sizing:border-box">not</em> assignment statements. This violates the <a href="https://en.wikipedia.org/wiki/Principle_of_least_astonishment" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">principle of least astonishment</a>. This presents difficulties for new language adopters by combining several concepts in a confusing form. They are arguably underutilized by language experts.</p><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">The status quo for the <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">=</code> operator is iteratively built up in this fashion:</p><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><li style="box-sizing:border-box"><code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">=</code> performs assignment</li><li style="box-sizing:border-box;margin-top:0.25em"><code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">let x =</code> performs binding</li><li style="box-sizing:border-box;margin-top:0.25em"><code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">if let x =</code> performs conditional binding on optionals</li><li style="box-sizing:border-box;margin-top:0.25em"><code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">if case .foo(let x) =</code> and <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">if case let .foo(x) =</code> performs conditional binding on enumerations <em style="box-sizing:border-box">and</em> applies pattern matching</li></ul><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">Both <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">guard case</code> and <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">if case</code> statements perform simultaneous pattern matching and conditional binding. Here are examples demonstrating their use in current Swift:</p><pre style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:16px;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-radius:3px;color:rgb(51,51,51)"><code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;padding:0px;margin:0px;background-color:transparent;border-radius:3px;word-break:normal;border:0px;display:inline;overflow:visible;line-height:inherit;word-wrap:normal">enum Result<T> { case success(T), error(Error) }
// valid Swift
guard case let .success(value) = result
else { ... }
// valid Swift
guard case .success(let value) = result
else { ... }
</code></pre><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">The problems with <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">guard case</code> and <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">if case</code> include:</p><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><li style="box-sizing:border-box">The <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">=</code> operator looks like assignment and not like pattern matching (<code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">~=</code>). </li><li style="box-sizing:border-box;margin-top:0.25em">The <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">case</code> layout is both too close to a <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">switch</code>'s <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">case</code> but doesn't follow its syntax. In <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">switch</code>, a <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">case</code> is followed by a colon, not an equal sign.</li><li style="box-sizing:border-box;margin-top:0.25em">Using the <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">case</code> syntax is unneccessarily wordy. It incorporates <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">case</code>, <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">=</code>, and optionally <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">let</code>/<code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">var</code> assignments<wbr>.</li></ul><h3 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;font-size:1.25em;line-height:1.25;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";background-color:rgb(255,255,255)"><a id="m_-4659585067960143237gmail-m_7548809065351022967user-content-indirect-and-direct-pattern-matching" class="m_-4659585067960143237gmail-m_7548809065351022967anchor" href="https://gist.github.com/erica/db9ce92b3d23cb20799460f603c0ae7c#indirect-and-direct-pattern-matching" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Indirect and Direct Pattern Matching</h3><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">Swift uses two kinds of pattern matching.</p><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><span style="box-sizing:border-box;font-weight:600">Indirect pattern matching</span> such as the kind you see in <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">switch</code> and <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">for</code> statements receives an argument in from the statement structure. The argument is not mentioned directly in the <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">case</code>:</p><pre style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:16px;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-radius:3px;color:rgb(51,51,51)"><code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;padding:0px;margin:0px;background-color:transparent;border-radius:3px;word-break:normal;border:0px;display:inline;overflow:visible;line-height:inherit;word-wrap:normal">switch value {
case .foo(let x): ... use x ...
...
}
for case .foo(let x) in collection { ... }
</code></pre><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><span style="box-sizing:border-box;font-weight:600">Direct pattern matching</span> including <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">guard</code>/<code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">if</code> st<wbr>atements and with the pattern matching operator place the argument to be matched to the right of an operator, either <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">=</code> or <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">~=</code>. The argument is explicitly mentioned:</p><pre style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:16px;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-radius:3px;color:rgb(51,51,51)"><code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;padding:0px;margin:0px;background-color:transparent;border-radius:3px;word-break:normal;border:0px;display:inline;overflow:visible;line-height:inherit;word-wrap:normal">if case .foo(let x) = value { ... use x ... }
if 100...200 ~= value { ... }
</code></pre><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">When using <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">if case</code>/<code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">guard case</code> in the absence of conditional binding, statements duplicate basic pattern matching with less obvious semantics. These following two statements are functionally identical. The second uses an assignment operator and the <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">case</code> keyword.</p><pre style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:16px;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-radius:3px;color:rgb(51,51,51)"><code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;padding:0px;margin:0px;background-color:transparent;border-radius:3px;word-break:normal;border:0px;display:inline;overflow:visible;line-height:inherit;word-wrap:normal">if range ~= myValue { ... } // simpler
if case range = myValue { ... } // confusing
</code></pre><h2 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;line-height:1.25;padding-bottom:0.3em;border-bottom:1px solid rgb(238,238,238);color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";background-color:rgb(255,255,255)"><a id="m_-4659585067960143237gmail-m_7548809065351022967user-content-detailed-design" class="m_-4659585067960143237gmail-m_7548809065351022967anchor" href="https://gist.github.com/erica/db9ce92b3d23cb20799460f603c0ae7c#detailed-design" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Detailed Design</h2><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">This proposal introduces the <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">unwrap</code> keyword. The <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">unwrap</code> statement shadows an enumeration variable to an unwrapped version of the same type. Upon adopting this proposal the following statements produce equivalent behvior:</p><div class="m_-4659585067960143237gmail-m_7548809065351022967highlight m_-4659585067960143237gmail-m_7548809065351022967highlight-source-swift" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:0px;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-radius:3px;word-break:normal"><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// New unwrap keyword</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> unwrap myValue { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// Existing same-name shadowing</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> myValue <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> myValue { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// Existing same-name pattern matching and conditional binding</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">some</span>(<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> myValue) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> myValue { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// old grammar</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">some</span>(myValue) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> myValue { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// old grammar</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// Proposed same-name pattern matching and conditional binding</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">some</span>(<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> myValue) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> myValue { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// new grammar</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">some</span>(myValue) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> myValue { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// new grammar</span></pre></div><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">In <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">if case</code> and <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">guard case</code>, this proposal drops the <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">case</code> keyword and replaces the equal sign with the pattern matching operator. The results look like this:</p><div class="m_-4659585067960143237gmail-m_7548809065351022967highlight m_-4659585067960143237gmail-m_7548809065351022967highlight-source-swift" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:0px;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-radius:3px;word-break:normal"><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">success</span>(value) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> result <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">success</span>(<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> value) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> result <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">success</span>(value) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> result { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">success</span>(<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> value) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> result { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> x<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">?</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> anOptional <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> x<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">?</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> anOptional { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }</pre></div><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">Users may choose to use <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">var</code> instead of <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">let</code> to bind to a variable instead of a constant. </p><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">In this update:</p><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><li style="box-sizing:border-box">The <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">case</code> keyword is subsumed into the (existing) pattern matching operator</li><li style="box-sizing:border-box;margin-top:0.25em">The statements adopt the existing <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">if-let</code> and <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">guard-let</code> <wbr>syntax, including <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">Optional</code> syntactic sugar.</li></ul><div class="m_-4659585067960143237gmail-m_7548809065351022967highlight m_-4659585067960143237gmail-m_7548809065351022967highlight-source-swift" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:0px;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-radius:3px;word-break:normal"><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> x <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> anOptional { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// current</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> x<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">?</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> anOptional { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// current, would be removed</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> x<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">?</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> anOptional { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// proposed replacement for `if case`</span></pre></div><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">On adopting this syntax, the two identical range tests naturally unify to this single version:</p><div class="m_-4659585067960143237gmail-m_7548809065351022967highlight m_-4659585067960143237gmail-m_7548809065351022967highlight-source-swift" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:0px;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-radius:3px;word-break:normal"><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> range <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> myValue { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// before</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> range <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> myValue { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// before</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> range <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> myValue { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// after</span></pre></div><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">Using pattern matching without conditional binding naturally simplifies to a standalone Boolean condition clause.</p><h3 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;font-size:1.25em;line-height:1.25;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";background-color:rgb(255,255,255)"><a id="m_-4659585067960143237gmail-m_7548809065351022967user-content-unwrap-and-non-optionals" class="m_-4659585067960143237gmail-m_7548809065351022967anchor" href="https://gist.github.com/erica/db9ce92b3d23cb20799460f603c0ae7c#unwrap-and-non-optionals" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a><code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:inherit;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">unwrap</code> and Non-Optionals</h3><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">Real world Swift enumerations rarely follow the Optional pattern, which can be summed up like this:</p><div class="m_-4659585067960143237gmail-m_7548809065351022967highlight m_-4659585067960143237gmail-m_7548809065351022967highlight-source-swift" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:0px;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-radius:3px;word-break:normal"><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">enum</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-en" style="box-sizing:border-box;color:rgb(121,93,163)">OptionalLike</span><<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-v" style="box-sizing:border-box;color:rgb(237,106,67)">T</span>> { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">aCaseWithOneAssociatedValue</span>(T)<wbr>, <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">anotherCase</span> }</pre></div><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">They more typically look like this:</p><div class="m_-4659585067960143237gmail-m_7548809065351022967highlight m_-4659585067960143237gmail-m_7548809065351022967highlight-source-swift" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:0px;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-radius:3px;word-break:normal"><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// One generic, one known type</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">enum</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-en" style="box-sizing:border-box;color:rgb(121,93,163)">Result</span><<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-v" style="box-sizing:border-box;color:rgb(237,106,67)">Value</span>> { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">success</span>(<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">Value</span>), <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">failure</span>(<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">Error</span>) }
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// Many cases of mixed types</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">enum</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-en" style="box-sizing:border-box;color:rgb(121,93,163)">JSON</span> {
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">string</span>(<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">String</span>)
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">number</span>(<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">Double</span>)
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">boolean</span>(<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">Bool</span>)
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">array</span>([JSON])
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">dictionary</span>([<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">String</span>: JSON])
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">null</span>
}
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// Multiple associated values</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">enum</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-en" style="box-sizing:border-box;color:rgb(121,93,163)">Response</span> { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">contact</span>(<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-en" style="box-sizing:border-box;color:rgb(121,93,163)"><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-smi" style="box-sizing:border-box;color:rgb(51,51,51)">code</span></span>: <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">Int</span>, <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-en" style="box-sizing:border-box;color:rgb(121,93,163)"><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-smi" style="box-sizing:border-box;color:rgb(51,51,51)">message</span></span>: <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">String</span>), <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">failure</span> }</pre></div><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">You can adapt the <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">bind</code> keyword to work with these real-world cases in one of two ways. The first way uses <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">unwrap</code>instead of <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">let</code> or <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">var</code>. Here are a few varieties of how that call might look versus the proposed update for normal pattern matching:</p><div class="m_-4659585067960143237gmail-m_7548809065351022967highlight m_-4659585067960143237gmail-m_7548809065351022967highlight-source-swift" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:0px;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-radius:3px;word-break:normal"><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> unwrap .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">string</span>(myString) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> json { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> unwrap .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">contact</span>(code, <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">_</span>) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> response { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> unwrap .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">contact</span>(code, <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">var</span> message) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> response { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)">// vs proposed</span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c" style="box-sizing:border-box;color:rgb(150,152,150)"></span>
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">string</span>(myString) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> json { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">var</span> .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">string</span>(myString) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> json { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">contact</span>(<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> code, <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">_</span>) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> response { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">contact</span>(<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> code, <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">var</span> message) <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> response { <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }</pre></div><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">Although slightly wordier than <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">let</code> and <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">var</code>, the <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">unwrap</code> solution offers advantages:</p><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><li style="box-sizing:border-box">It enhances readability. If the goal is to unwrap an embedded value, <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">unwrap</code> uses a more appropriate term.</li><li style="box-sizing:border-box;margin-top:0.25em">It establishes <em style="box-sizing:border-box">one</em> place for the keyword to live instead of the "does it go inside or outside" status quo. A consistent place means prettier code.</li><li style="box-sizing:border-box;margin-top:0.25em">As shown in these examples, it can easily be adapted for variable binding. If you want to override the let behavior, you can insert a var inside the parentheses.</li></ul><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">A second, riskier, cleaner approach looks like this. It assumes the compiler can pick up and shadow using either the associated value labels (preferred) or the enumeration name (as you'd see with <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">String</code> raw value enumerations):</p><div class="m_-4659585067960143237gmail-m_7548809065351022967highlight m_-4659585067960143237gmail-m_7548809065351022967highlight-source-swift" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:0px;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;background-color:rgb(247,247,247);border-radius:3px;word-break:normal"><span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> unwrap .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-smi" style="box-sizing:border-box">contact</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> response {
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> some compiler magic picks up on the `code` and `message` labels
used <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">for</span> initialization, so the bound variables are `code`
and `message`
}
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> unwrap .<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-smi" style="box-sizing:border-box">string</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> json {
<span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> use `string` <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-c1" style="box-sizing:border-box;color:rgb(0,134,179)">here</span> (same name <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">as</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">enum</span> <span class="m_-4659585067960143237gmail-m_7548809065351022967pl-k" style="box-sizing:border-box;color:rgb(167,29,93)">case</span>) because
no label was used to define the associated value
}</pre></div><h2 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;line-height:1.25;padding-bottom:0.3em;border-bottom:1px solid rgb(238,238,238);color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";background-color:rgb(255,255,255)"><a id="m_-4659585067960143237gmail-m_7548809065351022967user-content-impact-on-existing-code" class="m_-4659585067960143237gmail-m_7548809065351022967anchor" href="https://gist.github.com/erica/db9ce92b3d23cb20799460f603c0ae7c#impact-on-existing-code" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Impact on Existing Code</h2><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255)">This proposal is breaking and would require migration.</p><h2 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;line-height:1.25;padding-bottom:0.3em;border-bottom:1px solid rgb(238,238,238);color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";background-color:rgb(255,255,255)"><a id="m_-4659585067960143237gmail-m_7548809065351022967user-content-alternatives-considered" class="m_-4659585067960143237gmail-m_7548809065351022967anchor" href="https://gist.github.com/erica/db9ce92b3d23cb20799460f603c0ae7c#alternatives-considered" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Alternatives Considered</h2><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;color:rgb(51,51,51);font-family:-apple-system,blinkmacsystemfont,"segoe ui",helvetica,arial,sans-serif,"apple color emoji","segoe ui emoji","segoe ui symbol";font-size:16px;background-color:rgb(255,255,255);margin-bottom:0px"><li style="box-sizing:border-box">Leaving the grammar as-is, albeit confusing</li><li style="box-sizing:border-box;margin-top:0.25em">Retaining <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">case</code> and replacing the equal sign with <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">~=</code> (pattern matching) or <code style="box-sizing:border-box;font-family:consolas,"liberation mono",menlo,courier,monospace;font-size:13.6px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-radius:3px">:</code> (to match the switch statement).</li></ul><div><br></div></div></div><br></div></div><span class="">______________________________<wbr>_________________<br>
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