<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div></div><div>Why is exposing an Optional as an opaque box less error prone than an NSNull? That doesn't seem obviously true to me.</div><div><br>On Aug 24, 2016, at 8:00 PM, Charles Srstka via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html charset=us-ascii"><blockquote type="cite" class="">On Aug 24, 2016, at 8:27 PM, Greg Parker via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""></blockquote><div><blockquote type="cite" class=""><br class="Apple-interchange-newline"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><blockquote type="cite" class="" 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-stroke-width: 0px;"><div class="">On Aug 23, 2016, at 3:36 PM, Douglas Gregor 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 class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><h2 class="" style="box-sizing: border-box; margin-top: 24px; margin-bottom: 16px; line-height: 1.25; 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: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);">Proposed solution</h2><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">When an <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; 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;">Optional<T></code> value is bridged to an Objective-C object, if it contains <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; 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;">some</code> value, that value should be bridged; otherwise, <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; 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;">NSNull</code> or another sentinel object should be used.</p></div></div></blockquote><span 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-stroke-width: 0px; float: none; display: inline !important;" class="">I don't think I like this.</span></div><div class=""><br class=""></div><div class="">Let me verify my understanding. If I have this:</div><div class=""><br class=""></div><div class=""><font face="Menlo" class=""> // imported from ObjC</font></div><div class=""><font face="Menlo" class=""> func f(with object: Any)</font></div><div class=""><font face="Menlo" class=""> </font></div><div class=""><font face="Menlo" class=""> let s: String? = nil</font></div><div class=""><font face="Menlo" class=""> f(s)</font></div><div class=""><br class=""></div><div class="">then at runtime it will call </div><div class=""><font face="Menlo" class=""> f([NSNull null])</font></div><div class="">?</div><div class=""><br class=""></div><div class="">The problem is that NSNull is in fact rare in Cocoa. They are used in the Foundation containers and almost nowhere else. Passing NSNull into almost any API is going to do something confusing at runtime. If you're lucky you get a prompt error "-[NSNull something]: unrecognized selector". If you're not lucky you'll get that error somewhere much later, or something even less obviously related to NSNull and your call site. That sounds like the wrong outcome for developers who are confused or careless or unaware of an optional.</div></div></div></blockquote></div><br class=""><div class="">I agree, particularly since passing an array of optionals to an Objective-C API is much more likely to be the result of a typo or other programmer error than something actually intentional that ought to invoke the bridge.</div><div class=""><br class=""></div><div class="">Charles</div><div class=""><br class=""></div></div></blockquote><blockquote type="cite"><div><span>_______________________________________________</span><br><span>swift-evolution mailing list</span><br><span><a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a></span><br><span><a href="https://lists.swift.org/mailman/listinfo/swift-evolution">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br></div></blockquote></body></html>