<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="">The one downside I see to this is that it puts the ‘inout’ in a less prominent position. It looks fine after an argument name like ‘x’, but if the argument is named ‘textRepresentation’ or something longer like that, the ‘inout’ isn’t quite as noticeable as it is now, particularly if it’s in a long parameter list. In cases where the the inout parameter is the first one in the function call, the current position for ‘inout’ allows it to stand out nicely at the head of the line.<div class=""><br class=""></div><div class="">So a +/-1 for me.</div><div class=""><br class=""></div><div class="">The related idea of replacing ‘&’ with ‘inout’ at the call site seems completely contradictory to this proposal. Developers would then have to remember that the ‘inout’ goes before the argument at the call site but after it in the function definition. That seems like a constant source of mis-typings and something that would be viewed as an inconsistency in the language. Or do people want to put it after the argument name at the call site too? It seems a little like change just for the sake of change, IMO.<br class=""><div class=""><br class=""></div><div class="">—CK</div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jan 29, 2016, at 11:37 AM, Erica Sadun via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><a href="https://github.com/apple/swift-evolution/pull/127" class="">https://github.com/apple/swift-evolution/pull/127</a><div class=""><br class=""></div><div class=""><h1 id="adjustinginoutdeclarationsfortypedecoration" style="margin: 0px 0px 0.875em; font-size: 1.5em; line-height: 0.875em; font-family: 'Helvetica Neue', Helvetica, Arial, Verdana, sans-serif;" class="">Adjusting <code class="">inout</code> Declarations for Type Decoration</h1><ul style="color: rgb(17, 17, 17); font-family: 'Helvetica Neue', Helvetica, Arial, Verdana, sans-serif; font-size: 16px;" class=""><li style="font-size: 18px;" class="">Proposal: TBD</li><li style="font-size: 18px;" class="">Author(s): <a href="https://github.com/jckarter" style="color: rgb(13, 110, 161); text-decoration: none; transition: color 0.2s ease-in-out; -webkit-transition: color 0.2s ease-in-out;" class="">Joe Groff</a>, <a href="http://github.com/erica" style="color: rgb(13, 110, 161); text-decoration: none; transition: color 0.2s ease-in-out; -webkit-transition: color 0.2s ease-in-out;" class="">Erica Sadun</a></li><li style="font-size: 18px;" class="">Status: TBD</li><li style="font-size: 18px;" class="">Review manager: TBD</li></ul><h2 id="introduction" style="color: rgb(17, 17, 17); margin: 0px 0px 0.9545454545454546em; font-size: 1.375em; line-height: 0.9545454545454546em; font-family: 'Helvetica Neue', Helvetica, Arial, Verdana, sans-serif;" class="">Introduction</h2><p style="color: rgb(17, 17, 17); font-family: 'Helvetica Neue', Helvetica, Arial, Verdana, sans-serif; word-wrap: break-word; font-size: 1.1429em; line-height: 1.3125em; margin: 1.3125em 0px;" class="">The <code class="">inout</code> keyword indicates copy-in/copy-out argument behavior. In its current implementation<br class="">the keyword prepands argument names. We propose to move the <code class="">inout</code> keyword to the right<br class="">side of the colon to decorate the type instead of the parameter label. </p><p style="color: rgb(17, 17, 17); font-family: 'Helvetica Neue', Helvetica, Arial, Verdana, sans-serif; word-wrap: break-word; font-size: 1.1429em; line-height: 1.3125em; margin: 1.3125em 0px;" class=""><em class="">The initial Swift-Evolution discussion of this topic took place in the “Replace ‘inout’ with &” thread.</em></p><h2 id="motivation" style="color: rgb(17, 17, 17); margin: 0px 0px 0.9545454545454546em; font-size: 1.375em; line-height: 0.9545454545454546em; font-family: 'Helvetica Neue', Helvetica, Arial, Verdana, sans-serif;" class="">Motivation</h2><p style="color: rgb(17, 17, 17); font-family: 'Helvetica Neue', Helvetica, Arial, Verdana, sans-serif; word-wrap: break-word; font-size: 1.1429em; line-height: 1.3125em; margin: 1.3125em 0px;" class="">In Swift 2, the <code class="">inout</code> parameter lives on the label side rather than the type side of the colon<br class="">although the keyword isn’t modifying the label but its type. Decorating<br class="">types instead of labels offers identifiable advantages: </p><ul style="color: rgb(17, 17, 17); font-family: 'Helvetica Neue', Helvetica, Arial, Verdana, sans-serif; font-size: 16px;" class=""><li style="font-size: 18px;" class=""><div style="word-wrap: break-word; line-height: 1.3125em; margin: 0px;" class="">It enables the <code class="">inout</code> keyword to properly integrate into full type syntax, for example: </div><pre class=""><code class="swift coffeescript hljs" style="display: block; padding: 0.5em; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248); background-position: initial initial; background-repeat: initial initial;"><span class="hljs-function"><span class="hljs-params" style="color: rgb(153, 0, 0); font-weight: bold;">(x: inout T)</span> -></span> U <span class="hljs-regexp" style="color: rgb(0, 153, 38);">//</span><span class="hljs-function"> =></span> <span class="hljs-function"><span class="hljs-params" style="color: rgb(153, 0, 0); font-weight: bold;">(inout T)</span> -></span> U</code></pre></li><li style="font-size: 18px;" class=""><div style="word-wrap: break-word; line-height: 1.3125em; margin: 0px;" class="">It avoids notational similarity with arguments labeled <code class="">inout</code>, for example:</div><pre class=""><code class="swift coffeescript hljs" style="display: block; padding: 0.5em; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248); background-position: initial initial; background-repeat: initial initial;">func foo<span class="hljs-function"><span class="hljs-params" style="color: rgb(153, 0, 0); font-weight: bold;">(inOut x: T)</span> // <span class="hljs-title" style="color: rgb(153, 0, 0); font-weight: bold;">foo</span><span class="hljs-params" style="color: rgb(153, 0, 0); font-weight: bold;">(inOut:)</span>, <span class="hljs-title" style="color: rgb(153, 0, 0); font-weight: bold;">type</span> <span class="hljs-params" style="color: rgb(153, 0, 0); font-weight: bold;">(T)</span> -></span> Void
func foo<span class="hljs-function"><span class="hljs-params" style="color: rgb(153, 0, 0); font-weight: bold;">(inout x: T)</span> // <span class="hljs-title" style="color: rgb(153, 0, 0); font-weight: bold;">foo</span><span class="hljs-params" style="color: rgb(153, 0, 0); font-weight: bold;">(_:)</span>, <span class="hljs-title" style="color: rgb(153, 0, 0); font-weight: bold;">type</span> <span class="hljs-params" style="color: rgb(153, 0, 0); font-weight: bold;">(inout T)</span> -></span> Void</code></pre></li><li style="font-size: 18px;" class=""><div style="word-wrap: break-word; line-height: 1.3125em; margin: 0px;" class="">It better matches similar patterns in other languages such as borrowing in Rust, that may be later introduced back to Swift </div></li></ul><h2 id="detaileddesign" style="color: rgb(17, 17, 17); margin: 0px 0px 0.9545454545454546em; font-size: 1.375em; line-height: 0.9545454545454546em; font-family: 'Helvetica Neue', Helvetica, Arial, Verdana, sans-serif;" class="">Detailed design</h2><pre style="color: rgb(17, 17, 17); font-size: 16px;" class=""><code class=" lasso hljs" style="display: block; padding: 0.5em; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248); background-position: initial initial; background-repeat: initial initial;">parameter → external<span class="hljs-attribute" style="color: rgb(0, 128, 128);">-parameter</span><span class="hljs-attribute" style="color: rgb(0, 128, 128);">-name</span> optlocal<span class="hljs-attribute" style="color: rgb(0, 128, 128);">-parameter</span><span class="hljs-attribute" style="color: rgb(0, 128, 128);">-name</span> : <span class="hljs-keyword" style="font-weight: bold;">type</span><span class="hljs-attribute" style="color: rgb(0, 128, 128);">-annotation</span>
<span class="hljs-keyword" style="font-weight: bold;">type</span><span class="hljs-attribute" style="color: rgb(0, 128, 128);">-annotation</span> → inout <span class="hljs-keyword" style="font-weight: bold;">type</span><span class="hljs-attribute" style="color: rgb(0, 128, 128);">-annotation</span></code></pre><h2 id="alternativesconsidered" style="color: rgb(17, 17, 17); margin: 0px 0px 0.9545454545454546em; font-size: 1.375em; line-height: 0.9545454545454546em; font-family: 'Helvetica Neue', Helvetica, Arial, Verdana, sans-serif;" class="">Alternatives Considered</h2><p style="color: rgb(17, 17, 17); font-family: 'Helvetica Neue', Helvetica, Arial, Verdana, sans-serif; word-wrap: break-word; font-size: 1.1429em; line-height: 1.3125em; margin: 1.3125em 0px;" class="">Decorations using <code class="">@inout</code> (either <code class="">@inout(T)</code> or <code class="">@inout T</code>) were considered and discarded</p></div></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class="">https://lists.swift.org/mailman/listinfo/swift-evolution<br class=""></div></blockquote></div><br class=""></div></div></body></html>