<div dir="ltr">On Thu, Jun 2, 2016 at 12:42 AM, Austin Zheng via swift-evolution <span dir="ltr"><<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>></span> wrote:<br><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="word-wrap:break-word">Excellent.<div><br></div><div>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" target="_blank">https://github.com/austinzheng/swift-evolution/blob/ef6adbe0fe09bff6c44c6aa9d73ee407629235ce/proposals/0095-any-as-existential.md</a></div><div><br></div><div>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><br></div><div>My reasons:</div><div><br></div><div>- 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><br></div><div>- 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><br></div><div>- 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></blockquote><div><br></div><div>Agree with your reasons, but I'm still uncomfortable that things inside the angle brackets would behave differently here than elsewhere. Would it help to make a keyword out of `any` for existentials? Then you could have this:</div><div><br></div><div>```</div><div><div style="font-size:13px">func foo(value: any X & Y)</div></div><div>```</div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="word-wrap:break-word"><div>Best,</div><div>Austin</div><span class=""><div><br><div><blockquote type="cite"><div>On Jun 1, 2016, at 10:17 PM, Chris Lattner <<a href="mailto:clattner@apple.com" target="_blank">clattner@apple.com</a>> wrote:</div><br><div><div><br><blockquote type="cite">On Jun 1, 2016, at 9:53 PM, Austin Zheng <<a href="mailto:austinzheng@gmail.com" target="_blank">austinzheng@gmail.com</a>> wrote:<br><br>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><br>One quick question - is making whatever syntax is chosen for Swift 3 "forward-compatible" with a future generalized existential feature a concern?<br></blockquote><br>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><br>-Chris</div></div></blockquote></div><br></div></span></div><br>_______________________________________________<br>
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