<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 May 10, 2016, at 2:49 PM, Matthew Johnson via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><div class=""><blockquote type="cite" 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;" class=""><div class=""><div class="">That said, I’m not sure I understand the concrete use-cases. When is this concept important? When is “Self” not good enough?</div></div></blockquote><div 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;" class=""><br class=""></div><div 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;" class="">The only case where there is new functionality is when this is used in a protocol requirement. I gave an example earlier today. </div></div></blockquote></div><br class=""><div class="">This functionality is the key: Ability of an open (non-final) class to conform to a protocol that lets it return an instance of the conforming type (itself). Self does not work for that and we can’t change its behavior (or can we?) So one solution seems to be Matt’s proposal. This functionality is important for me and an example use case is class clusters. For the client code it is sealed and acts just like a final class, but internally it may return a subclass that is an implementation detail. We should be able to do this.</div><div class=""><br class=""></div><div class="">Hooman</div></body></html>