<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div></div><div><br></div><div><br>Am 23.05.2016 um 00:18 schrieb Austin Zheng via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>:<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html charset=utf-8">I agree; the difference between protocols with and without associated types has been an endless source of confusion for a lot of people.<div class=""><br class=""></div><div class="">Speaking of which, for those who care I rewrote the draft proposal to attempt a much more rigorous treatment of the semantics of the generalized existential, including a discussion about existential type equivalence and subtyping. It would be nice to see people poke holes in my logic so I can patch them up. <a href="https://github.com/austinzheng/swift-evolution/blob/az-existentials/proposals/XXXX-enhanced-existentials.md" class="">https://github.com/austinzheng/swift-evolution/blob/az-existentials/proposals/XXXX-enhanced-existentials.md</a></div></div></blockquote><div><br></div>I think that *all* methods should be available - at least in principle - with associated types <div>- replaced by their upper bounds (i.e. Any if no constraints have been given either by the protocol definition itself or th existential) if in covariant position and </div><div>- replaced by their lower bounds if in contravariant position</div><div><br></div><div>As it is not possible to define lower bounds in Swift, the lower bounds are always the bottom type (called `Nothing` in Swift and not be confused with optionals). The bottom type has no members and therefore a method referencing that type cannot be called and is effectively not available.</div><div><br></div><div>-Thorsten </div><div><br><blockquote type="cite"><div><div class=""><br class=""></div><div class="">Austin<br class=""><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On May 22, 2016, at 3:05 PM, Russ Bishop 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=""><br class=""><blockquote type="cite" class="">On May 17, 2016, at 1:55 PM, Joe Groff via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class="">I agree with this. If we're certain we should reskin protocol<> as Any<>, we should frontload that change—in addition to affecting source code, it'd also influence the runtime behavior of type printing/parsing, which can't be statically migrated in the future. I think any discussion of extending existentials has to be considered out of scope for Swift 3, though, so the Any rename deserves its own proposal.<br class=""><br class="">-Joe<br class=""></blockquote><br class=""><br class="">Its really unfortunate that the generics work is probably going to be deferred. When you really dive in to protocol-oriented programming and designing frameworks to be native Swift (taking advantage of Swift features) the existential problem comes up a lot and leads to sub-optimal designs, abandonment of type safety, or gobs of boilerplate. <br class=""><br class=""><br class="">Russ<br class=""><br class="">_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></div></div></blockquote></div><br class=""></div></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></div></body></html>