<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 24 Jul 2016, at 01:26, Chris Lattner 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="">Hello Swift community,<br class=""><br class="">The review of "SE-0131: Add AnyHashable to the standard library" begins now and runs through July 25. This proposal is a bit unusual, since it is a late additive proposal. The reason we need to do something here is as a critical part of "SE-0116: Import Objective-C id as Swift Any type”, enabling importing untyped NSDictionary's and NSSet’s properly. The core team considers this already conceptually approved for Swift 3 as part of SE-0116, but would greatly appreciate feedback on the details of the proposed design.<br class=""><br class="">The proposal is available here:<br class=""><br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><a href="https://github.com/apple/swift-evolution/blob/master/proposals/0131-anyhashable.md" class="">https://github.com/apple/swift-evolution/blob/master/proposals/0131-anyhashable.md</a><br class=""><br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>* What is your evaluation of the proposal?<br class=""></div></div></blockquote><div><br class=""></div><div>+1, this is a nice addition, and useful at times.</div><div><br class=""></div><div>There's one <a href="https://swiftlang.ng.bluemix.net/#/repl/c1ddd24113169ab82df118660c8e0de6ea24e48d32997c327638a88dc686e91f" class="">very obscure gotcha</a> with AnyHashable that subclass instances of a Hashable base class should be cast to the base type before wrapping into AnyHashable, otherwise such wrapped values may break the equivalence law of symmetry (`a == b` iff `b == a`).</div><div><br class=""></div><div>But now that most of Foundation's class clusters are bridged into value types, that problem is unlikely to occur to anyone anymore.</div><div><br class=""></div><blockquote type="cite" class=""><div class=""><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>* Is the problem being addressed significant enough to warrant a change to Swift?<br class=""></div></div></blockquote><div><br class=""></div><div>So and so.</div><br class=""><blockquote type="cite" class=""><div class=""><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>* Does this proposal fit well with the feel and direction of Swift?<br class=""></div></div></blockquote><div><br class=""></div><div>Yes. Maybe it will also help us gain more experience when designing real existential types.</div><br class=""><blockquote type="cite" class=""><div class=""><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>* If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?<br class=""></div></div></blockquote><div><br class=""></div><div>A bit of a hack compared to real existentials. But a good one.</div><br class=""><blockquote type="cite" class=""><div class=""><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>* How much effort did you put into your review? A glance, a quick reading, or an in-depth study?<br class=""></div></div></blockquote></div><br class=""><div class="">Quick reading.</div><div class=""><br class=""></div><div class="">— Pyry</div><div class=""><br class=""></div></body></html>