<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">Le 25 mai 2017 à 17:47, Nate Cook via swift-evolution &lt;<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>&gt; a écrit :</div><br class="Apple-interchange-newline"><div class=""><div dir="auto" class=""><div class=""><div class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><div class=""><blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class=""><font class=""><span style="background-color: rgba(255, 255, 255, 0);" class="">For consistency, the decision was to make closure parameter lists work the same way as function parameters. Function parameters do not allow destructuring of arguments in their declaration, so it seemed weird to let closures do that.</span></font></blockquote><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="background-color: rgba(255, 255, 255, 0);" class=""><br class=""></span></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="background-color: rgba(255, 255, 255, 0);" class="">I have to say that for me, it has never seemed weird at the use site to destructure tuples like that. The only confusion I've ever seen from users is when deconstruction didn't work enough, like if the parameter was (Int, (Int, Int)) and you couldn't destructure the nested tuple.</span></div></div></div></div></div></div></div></div></div></blockquote><br class=""></div><div>I even suggest that tuple destructuring gets more consideration.</div><div><br class=""></div><div>That is because without restructuring, many closures that could be written as a single line have to be written with several lines (in order to explicitly destructure input tuples, as in the sample code provided by the OP):</div><div><br class=""></div><div><span style="font-family: Menlo;" class="">+ &nbsp; &nbsp; &nbsp; &nbsp;self.forEach&nbsp;{ (arg)&nbsp;in</span><br class="" style="font-family: Menlo;"><span style="font-family: Menlo;" class="">+ &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;let&nbsp;(keyItem, valueItem)&nbsp;=&nbsp;arg</span><br class="" style="font-family: Menlo;"></div><div><br class=""></div><div>Unfortunately, multiline closures are less nice than single line closures: multiline closures can't avoid the `return` keyword. And multiline closures have downgraded type inference:</div><div><br class=""></div><div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> f&lt;T&gt;(</span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class=""> closure: () -&gt; </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">T</span><span style="font-variant-ligatures: no-common-ligatures" class="">) -&gt; </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">T</span><span style="font-variant-ligatures: no-common-ligatures" class=""> { </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> closure() }</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(0, 132, 0);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">// Yeah!</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">f</span><span style="font-variant-ligatures: no-common-ligatures" class=""> { </span><span style="font-variant-ligatures: no-common-ligatures; color: #272ad8" class="">1</span><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(0, 132, 0);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">// Meh: unable to infer complex closure return type; add explicit type to disambiguate</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">f</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">&nbsp; &nbsp; </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> x = </span><span style="font-variant-ligatures: no-common-ligatures; color: #272ad8" class="">1</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">&nbsp; &nbsp; </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> x</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div></div><div><br class=""></div><div>Of course, the type inference problem above could be fixed independently of tuple destructuring. But it looks like it is difficult to implement: see Jordan Rose's comment in&nbsp;<a href="https://bugs.swift.org/browse/SR-1570" class="">https://bugs.swift.org/browse/SR-1570</a>&nbsp;which links to&nbsp;<a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/002583.html" class="">https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/002583.html</a>.</div><div><br class=""></div><div>Gwendal Roué</div><div><br class=""></div></body></html>