<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=""><div class="">Excellent! I’m glad to see someone pick this up (and interest this time! I was disheartened earlier by lack of discussion when I proposed this)</div><div class=""><br class=""></div><div class="">One initial bit of feedback - I believe if you have existential types, I believe you can define Sequence Element directly, rather than with a type alias. e.g.</div><div class=""><div class=""><br class=""></div><div class="">protocol Sequence {</div><div class=""> associatedtype Element</div><div class=""> associatedtype Iterator: any<IteratorProtocol where IteratorProtocol.Element==Element> </div><div class=""> associatedtype SubSequence: any<Sequence where Sequence.Element == Element></div><div class=""> …</div><div class="">}</div><div class=""><br class=""></div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On May 22, 2016, at 6:18 PM, Austin Zheng 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="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;"><br class="Apple-interchange-newline">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 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;"><br class=""></div><div 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;">Austin</div></div></blockquote></div><br class=""></div></div></body></html>