<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div><br><br>Sent from my iPhone</div><div><br>On Jan 4, 2017, at 8:40 PM, Derrick Ho <<a href="mailto:wh1pch81n@gmail.com">wh1pch81n@gmail.com</a>> wrote:<br><br></div><blockquote type="cite"><div>So could we add a @trailing or @nontrailing to the block argument to toggle on and off the feature?<br></div></blockquote><div><br></div> But... why? That's a nontrivial amount of complexity for a fairly limited use case. <div><br></div><div> - Doug</div><div><br><blockquote type="cite"><div><br><br><div class="gmail_quote"><div dir="ltr">On Wed, Jan 4, 2017 at 8:35 PM Douglas Gregor via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="auto" class="gmail_msg"><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">On Jan 4, 2017, at 7:48 PM, Saagar Jha via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a>> wrote:<br class="gmail_msg"><br class="gmail_msg"></div><blockquote type="cite" class="gmail_msg"><div class="gmail_msg">Check out <a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160606/020470.html" class="gmail_msg" target="_blank">this thread</a>–it’s very similar to what you proposed, but it didn’t go anywhere. FWIW +1 to this as well as the ability to use multiple trailing closures like so:<div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">animate(identifier: “”, duration: 0, update: {</div><div class="gmail_msg"><span class="m_3277681189286428966Apple-tab-span gmail_msg" style="white-space:pre-wrap"> </span>// update</div><div class="gmail_msg">}, completion: {</div><div class="gmail_msg"><span class="m_3277681189286428966Apple-tab-span gmail_msg" style="white-space:pre-wrap"> </span>// completion</div><div class="gmail_msg">}</div><div class="gmail_msg"><div class="gmail_msg">
<br class="m_3277681189286428966Apple-interchange-newline gmail_msg"><span style="color:rgb(0,0,0);font-family:'SF UI Text';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;float:none;display:inline!important" class="gmail_msg">Saagar Jha</span><br style="color:rgb(0,0,0);font-family:'SF UI Text';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" class="gmail_msg"><br style="color:rgb(0,0,0);font-family:'SF UI Text';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" class="gmail_msg"><br style="color:rgb(0,0,0);font-family:'SF UI Text';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" class="gmail_msg">
</div>
<br class="gmail_msg"><div class="gmail_msg"><blockquote type="cite" class="gmail_msg"><div class="gmail_msg">On Jan 4, 2017, at 6:25 PM, Jay Abbott via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a>> wrote:</div><br class="m_3277681189286428966Apple-interchange-newline gmail_msg"><div class="gmail_msg"><div dir="ltr" class="gmail_msg"><div class="m_3277681189286428966markdown-here-wrapper gmail_msg"><p style="margin:0px 0px 1.2em!important" class="gmail_msg">When you have a function with a closure and then another optional default <code style="font-size:1em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline" class="gmail_msg">= nil</code> closure at the end, like this:</p>
<pre style="font-size:1em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em 0px" class="gmail_msg"><code class="m_3277681189286428966language-swift m_3277681189286428966hljs gmail_msg" style="font-size:1em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline;white-space:pre-wrap;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important;display:block;overflow-x:auto;padding:0.5em;color:rgb(51,51,51);background:rgb(248,248,248) none repeat scroll 0% 0%">open <span class="m_3277681189286428966hljs-keyword gmail_msg" style="color:rgb(51,51,51);font-weight:bold">static</span> <span class="m_3277681189286428966hljs-func gmail_msg"><span class="m_3277681189286428966hljs-keyword gmail_msg" style="color:rgb(51,51,51);font-weight:bold">func</span> <span class="m_3277681189286428966hljs-title gmail_msg" style="color:rgb(153,0,0);font-weight:bold">animate</span><span class="m_3277681189286428966hljs-params gmail_msg">(identifier: String,
duration: Double,
update: @escaping AnimationUpdate,
completion: AnimationCompletion? = <span class="m_3277681189286428966hljs-built_in gmail_msg" style="color:rgb(0,134,179)">nil</span>)</span> </span>{
</code></pre><p style="margin:0px 0px 1.2em!important" class="gmail_msg">You can’t use trailing closure syntax for the <code style="font-size:1em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline" class="gmail_msg">update</code> argument when leaving the <code style="font-size:1em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline" class="gmail_msg">completion</code> argument out/default.</p><p style="margin:0px 0px 1.2em!important" class="gmail_msg">This kind of breaks one of the benefits of default arguments, which is that you can add them to existing released functions without breaking the calling code. This means you have to add a separate convenience function without the extra argument, which is annoying and inelegant. </p></div></div></div></blockquote></div></div></div></blockquote></div><div dir="auto" class="gmail_msg"><div class="gmail_msg">Why not simply add the "completion" parameter before the trailing closure? That would still allow existing callers to work, without having to change the language. </div></div><div dir="auto" class="gmail_msg"><br class="gmail_msg"><blockquote type="cite" class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg"><blockquote type="cite" class="gmail_msg"><div class="gmail_msg"><div dir="ltr" class="gmail_msg"><div class="m_3277681189286428966markdown-here-wrapper gmail_msg"><p style="margin:0px 0px 1.2em!important" class="gmail_msg">Another annoying thing is that you can easily miss this error if you happen to not use trailing closure syntax in your tests or other usage, because adding the extra default argument compiles fine for code that uses normal syntax.</p></div></div></div></blockquote></div></div></div></blockquote></div><div dir="auto" class="gmail_msg"><div class="gmail_msg">The Swift compiler warns when a parameter written as a closure type isn't the last parameter. The warning is actually disabled in the specific case above because you've written it using a typealias... maybe we should warn on such cases (it's worth a bug report). Regardless, in the majority of instances, you'll get a warning, so it won't be silent on disabling trailing closure syntax. </div></div><div dir="auto" class="gmail_msg"><br class="gmail_msg"><blockquote type="cite" class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg"><blockquote type="cite" class="gmail_msg"><div class="gmail_msg"><div dir="ltr" class="gmail_msg"><div class="m_3277681189286428966markdown-here-wrapper gmail_msg"><p style="margin:0px 0px 1.2em!important" class="gmail_msg">Are there any issues/gotchas if the trailing closure syntax were to work for the last <em class="gmail_msg">specified</em> argument rather than the last <em class="gmail_msg">defined</em> argument?</p></div></div></div></blockquote></div></div></div></blockquote></div><div dir="auto" class="gmail_msg"><div class="gmail_msg">The main gotcha, and the reason the rule is the way it is, is that it means you'd lose trailing closure syntax if the caller wanted to specify an argument for the last parameter.</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg"> - Doug</div></div><div dir="auto" class="gmail_msg"><div class="gmail_msg"><br class="gmail_msg"></div><br class="gmail_msg"><blockquote type="cite" class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg"><blockquote type="cite" class="gmail_msg"><div class="gmail_msg"><div dir="ltr" class="gmail_msg"><div class="m_3277681189286428966markdown-here-wrapper gmail_msg">
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