<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 Apr 11, 2016, at 11:41 , Dave Abrahams 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=""><br style="font-family: Monaco; font-size: 11px; 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=""><span style="font-family: Monaco; font-size: 11px; 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="">on Mon Apr 11 2016, Charles Srstka <</span><a href="http://cocoadev-at-charlessoft.com/" style="font-family: Monaco; font-size: 11px; 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="">cocoadev-AT-charlessoft.com</a><span style="font-family: Monaco; font-size: 11px; 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="">> wrote:</span><br style="font-family: Monaco; font-size: 11px; 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: Monaco; font-size: 11px; 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: Monaco; font-size: 11px; 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=""> On Apr 11, 2016, at 12:03 PM, Dave Abrahams via swift-evolution<br class=""> <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""> on Sun Apr 10 2016, Dietmar Planitzer <<a href="http://dplanitzer-at-q.com" class="">dplanitzer-AT-q.com</a>> wrote:<br class=""><br class=""> On Apr 10, 2016, at 11:46, Dave Abrahams via swift-evolution<br class=""><br class=""> <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""> on Sun Apr 10 2016, Dietmar Planitzer <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>><br class=""><br class=""> wrote:<br class=""><br class=""> I’m not sure whether you’ve read the conclusion of my<br class=""> mail since<br class=""> you’ve only commented on the introductory part. In the<br class=""> conclusion I<br class=""> wrote that a possible approach for the replacement of ObjC-style<br class=""> optional protocol methods would be:<br class=""><br class=""> 1) the default implementation of a protocol method must be<br class=""> defined<br class=""><br class=""> in<br class=""><br class=""> the protocol (so just like in native Swift protocols today).<br class=""><br class=""> ? They can and must be defined in protocol extensions today.<br class=""><br class=""> I know.<br class=""><br class=""> 2) we add a way for a protocol provider to check whether the<br class=""><br class=""> protocol<br class=""><br class=""> adopter has provided an “override” of the default method.<br class=""><br class=""> I object to this part.<br class=""><br class=""> You object why? I do understand why you object to the ObjC model since<br class=""> there is not necessarily an implementation of the protocol method and<br class=""> thus the protocol provider has to guard every call with an existence<br class=""> check. But in this model here we would be guaranteed that there would<br class=""> be an implementation of the protocol method and thus guarding the call<br class=""> wouldn’t be necessary.<br class=""><br class=""> Because it's a needless complication that will encourage protocol and<br class=""> algorithm designers to create inefficient programs because they know the<br class=""> user can fall back on this hack. Nobody thinks that classes need the<br class=""> ability to check whether a given method is overridden. Why should this<br class=""> be needed for protocols?<br class=""><br class="">Actually, Apple’s frameworks have often contained code to check whether given<br class="">methods are overridden, and this has allowed them to deprecate override points<br class="">and replace them with better API without breaking source or binary<br class="">compatibility. The most obvious example that comes to mind is NSDocument; when<br class="">they introduced the newer override points such as -readFromURL:ofType:error:<br class="">that used NSURLs instead of paths and allowed returning an NSError, they added<br class="">code in the default implementation to check whether the subclass overrode the<br class="">older -readFromFile:ofType: method and if it did, called that method. Otherwise,<br class="">it would call the modern methods. This way, older applications that were still<br class="">overriding -readFromFile:ofType: would continue to work correctly.<br class=""></blockquote><br style="font-family: Monaco; font-size: 11px; 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=""><span style="font-family: Monaco; font-size: 11px; 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 believe we're aiming to support this kind of evolution in Swift,</span><br style="font-family: Monaco; font-size: 11px; 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=""><span style="font-family: Monaco; font-size: 11px; 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="">but others understand our resilience plans better than I, so we should</span><br style="font-family: Monaco; font-size: 11px; 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=""><span style="font-family: Monaco; font-size: 11px; 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="">probably let them comment.</span><br style="font-family: Monaco; font-size: 11px; 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=""></div></blockquote></div><br class=""><div class="">It's a useful enough pattern that I wouldn't want to rule it out entirely, but it's rare enough that it could be some strange runtime call. (Also, in many cases there's a simpler implementation, like "call the old method unilaterally".)</div><div class=""><br class=""></div><div class="">Jordan</div><div class=""><br class=""></div></body></html>