<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 Mar 15, 2016, at 10:03 PM, Chris Willmore 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 style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Hi, swift-evolution,</div><div class=""><br class=""></div><div class="">Some colleagues and I have been working on a <a href="https://github.com/cwillmor/swift-evolution/blob/master/proposals/0000-abolish-iuo.md" class="">proposal</a> to remove the ImplicitlyUnwrappedOptional type from Swift and replace it with an IUO decl attribute. Please have a look; I would greatly appreciate any comments you have before I push this proposal forward.</div><div class=""><br class=""></div><div class=""><a href="https://github.com/cwillmor/swift-evolution/blob/master/proposals/0000-abolish-iuo.md" class="">https://github.com/cwillmor/swift-evolution/blob/master/proposals/0000-abolish-iuo.md</a></div><div class=""><br class=""></div><div class="">Thanks,</div><div class="">— Chris Willmore</div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><h1 style="box-sizing: border-box; font-size: 2.25em; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.2; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class="">Abolish <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-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">ImplicitlyUnwrappedOptional</code> type</h1><ul style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class=""><li style="box-sizing: border-box;" class="">Proposal: SE-NNNN</li><li style="box-sizing: border-box;" class="">Author: <a href="http://github.com/cwillmor" style="box-sizing: border-box; background-color: transparent; color: rgb(64, 120, 192); text-decoration: none;" class="">Chris Willmore</a></li><li style="box-sizing: border-box;" class="">Status: TBD</li><li style="box-sizing: border-box;" class="">Review Manager: TBD</li></ul><p style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class="">This proposal seeks to remove the <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">ImplicitlyUnwrappedOptional</code> type from the Swift type system and replace it with an IUO attribute on declarations. Appending <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">!</code> to the type of a Swift declaration will give it optional type and annotate the declaration with an attribute stating that it (or, in the case of a function, the return value of its application) may be implicitly unwrapped.</p><h2 style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a id="user-content-motivation" class="anchor" href="https://github.com/cwillmor/swift-evolution/blob/89971a8162eba3aeb238d47772cda295a02cc585/proposals/0000-abolish-iuo.md#motivation" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1;"><svg aria-hidden="true" class="octicon octicon-link" height="16" role="img" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>Motivation</h2></div></div></div></blockquote><br class=""></div><div><br class=""></div><div>Let me play devil’s advocate: why not just get rid of implicit unwrapping entirely?</div><div><br class=""></div><div>Apple’s Objective-C APIs have had plenty of time to be audited by now. Anything not annotated can be assumed to be optional (which is the safest bet). </div><div><br class=""></div><div>The only case where IUOs are necessary is when you can’t cram something into the Swift initialization patterns (view controllers with outlets are the primary example). Having an attribute to suppress the compiler errors about failing to initialize outlet properties solves that problem (and any similar initialization problem) while limiting the scope. For example:</div><div><span class="Apple-tab-span" style="white-space:pre"> </span></div><div><font face="Monaco" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>@noinit @IBOutlet var view: UIView</font></div><div><br class=""></div><div>I’ve gotten into the habit of treating `!` as if it were `?` anyway and it hasn’t steered me wrong yet.</div><div><br class=""></div><div><br class=""></div><div>Russ</div><br class=""></body></html>