<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div><br><br>Sent from my iPad</div><div><br>On Jun 2, 2016, at 12:42 AM, Austin Zheng 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=utf-8">Excellent.<div class=""><br class=""></div><div class="">I put together a PR with a revised proposal containing the core team's recommended approach. If anyone is curious they can see it here: <a href="https://github.com/austinzheng/swift-evolution/blob/ef6adbe0fe09bff6c44c6aa9d73ee407629235ce/proposals/0095-any-as-existential.md" class="">https://github.com/austinzheng/swift-evolution/blob/ef6adbe0fe09bff6c44c6aa9d73ee407629235ce/proposals/0095-any-as-existential.md</a></div><div class=""><br class=""></div><div class="">Since this is the de-facto second round discussion thread, I'll start with my personal opinion (which is *not* reflected in the PR): the '&' separators in lieu of commas are a good idea, but I would still prefer the types to be wrapped in "Any<>", at least when being used as existentials.</div></div></blockquote><div><br></div>Thanks for writing up the revision Austin, especially since it does not reflect your own opinion.<div><br></div><div>My opinion is that we should view these as type expressions. We don't require any kind of delimiters around value expressions, allowing optional parentheses for clarification and as a matter of style. I don't see any reason to treat type expressions any different than that syntactically. </div><div><div><br><blockquote type="cite"><div><div class=""><br class=""></div><div class="">My reasons:</div><div class=""><br class=""></div><div class="">- Jordan Rose brought up a good point in one of the discussion threads today: a resilience goal is to allow a library to add an associated type to a protocol that had none and not have it break user code. If this is true whatever syntax is used for existentials in Swift 3 should be a valid subset of the generalized existential syntax used to describe protocol compositions with no associated types.</div><div class=""><br class=""></div><div class="">- I would rather have "Any<>" be used consistently across all existential types eventually than have it only be used for (e.g.) existential types with `where` constraints, or allowing two different representations of the same existential type (one with Any, and one without).</div><div class=""><br class=""></div><div class="">- I think any generalized existential syntax without delimiting markers (like angle braces) is harder to read than syntax with such markers, so I would prefer a design with those markers.</div><div class=""><br class=""></div><div class="">Best,</div><div class="">Austin</div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jun 1, 2016, at 10:17 PM, Chris Lattner <<a href="mailto:clattner@apple.com" class="">clattner@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class=""><br class=""><blockquote type="cite" class="">On Jun 1, 2016, at 9:53 PM, Austin Zheng <<a href="mailto:austinzheng@gmail.com" class="">austinzheng@gmail.com</a>> wrote:<br class=""><br class="">This was indeed a very thorough review by the core team. I'll prepare a v2 proposal with this feedback taken into account so we can continue moving things along.<br class=""><br class="">One quick question - is making whatever syntax is chosen for Swift 3 "forward-compatible" with a future generalized existential feature a concern?<br class=""></blockquote><br class="">Yes it is a concern, but we assume that the “X & Y” syntax will always be accepted going forward, as sugar for the more general feature that is yet to be designed.<br class=""><br class="">-Chris</div></div></blockquote></div><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></div></div></body></html>