<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="">On Jan 4, 2017, at 9:32 PM, Saagar Jha <<a href="mailto:saagar@saagarjha.com" class="">saagar@saagarjha.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div class="">
<br class="Apple-interchange-newline"><span style="font-family: 'SF UI Text'; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">Saagar Jha</span><br style="font-family: 'SF UI Text'; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br style="font-family: 'SF UI Text'; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br style="font-family: 'SF UI Text'; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">
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<br class=""><div class=""><blockquote type="cite" class=""><div class="">On Jan 4, 2017, at 8:35 PM, Douglas Gregor <<a href="mailto:dgregor@apple.com" class="">dgregor@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div style="font-family: SFUIText-Regular; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class="Apple-interchange-newline">On Jan 4, 2017, at 7:48 PM, Saagar Jha via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""></div><blockquote type="cite" style="font-family: SFUIText-Regular; 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=""><div class="">Check out <a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160606/020470.html" class="">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=""><br class=""></div><div class="">animate(identifier: “”, duration: 0, update: {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>// update</div><div class="">}, completion: {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>// completion</div><div class="">}</div><div class=""><div class=""><br class="Apple-interchange-newline"><span class="" style="font-family: 'SF UI Text'; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;">Saagar Jha</span><br class="" style="font-family: 'SF UI Text'; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class="" style="font-family: 'SF UI Text'; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class="" style="font-family: 'SF UI Text'; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"></div><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Jan 4, 2017, at 6:25 PM, Jay Abbott via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div class="markdown-here-wrapper"><p class="" style="margin: 0px 0px 1.2em !important;">When you have a function with a closure and then another optional default<span class="Apple-converted-space"> </span><code class="" 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-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; display: inline;">= nil</code><span class="Apple-converted-space"> </span>closure at the end, like this:</p><pre class="" style="font-family: Consolas, Inconsolata, Courier, monospace; font-size: 1em; line-height: 1.2em; margin: 1.2em 0px;"><code class="language-swift hljs" style="font-size: 1em; font-family: Consolas, Inconsolata, Courier, monospace; margin: 0px 0.15em; white-space: pre; overflow: auto; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; border: 1px solid rgb(204, 204, 204); padding: 0.5em; color: rgb(51, 51, 51); background-image: none; background-attachment: scroll; background-color: rgb(248, 248, 248); display: block !important; background-position: 0% 0%; background-repeat: repeat repeat;">open <span class="hljs-keyword" style="color: rgb(51, 51, 51); font-weight: bold;">static</span> <span class="hljs-func"><span class="hljs-keyword" style="color: rgb(51, 51, 51); font-weight: bold;">func</span> <span class="hljs-title" style="color: rgb(153, 0, 0); font-weight: bold;">animate</span><span class="hljs-params">(identifier: String,
duration: Double,
update: @escaping AnimationUpdate,
completion: AnimationCompletion? = <span class="hljs-built_in" style="color: rgb(0, 134, 179);">nil</span>)</span> </span>{
</code></pre><p class="" style="margin: 0px 0px 1.2em !important;">You can’t use trailing closure syntax for the<span class="Apple-converted-space"> </span><code class="" 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-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; display: inline;">update</code><span class="Apple-converted-space"> </span>argument when leaving the<span class="Apple-converted-space"> </span><code class="" 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-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; display: inline;">completion</code><span class="Apple-converted-space"> </span>argument out/default.</p><p class="" style="margin: 0px 0px 1.2em !important;">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 style="font-family: SFUIText-Regular; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">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><br style="font-family: SFUIText-Regular; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><blockquote type="cite" style="font-family: SFUIText-Regular; 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=""><div class=""><div class=""><div class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class="markdown-here-wrapper"><p class="" style="margin: 0px 0px 1.2em !important;">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 style="font-family: SFUIText-Regular; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">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></blockquote><div class=""><br class=""></div><div class="">Tried this out in the playground:</div><div class=""><br class=""></div><div class="">func foo(a: () -> (), b: (() -> ())? = nil) {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>a()</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>b?()</div><div class="">}</div><div class=""><br class=""></div><div class="">foo(a: {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>print(“Bar”)</div><div class="">})</div><div class=""><br class=""></div><div class="">and didn’t receive a warning for it, either.</div></div></div></div></blockquote></div><br class=""><div class="">We don’t warn here because ‘foo’ does have a trailing closure… it’s for the second parameter. I guess we could still warn about ‘a’ (maybe lump it into the same bug about the typealias case).</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- Doug</div><div class=""><br class=""></div></body></html>