<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Composing a base class and protocol requirements opens up the possibility of using the base class to constrain away a protocol's associated types, e.g.:<div class=""><br class=""></div><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class=""><div class="">protocol P { associatedtype T; func foo(_: T) }</div></blockquote><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class=""><div class="">class C<T>: P { func foo(_: T) {}</div></blockquote><div class=""><br class=""></div><div class="">It'd be worth calling out explicitly whether this proposal allows `C<T> & P` to be used as an existential type, since although P has free associated types, the composition does not.</div><div class=""><br class=""></div><div class="">-Joe</div><div class=""><br class=""><blockquote type="cite" class="">On Feb 28, 2017, at 1:11 PM, Douglas Gregor via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class="">Hello Swift community,<br class=""><br class="">The review of SE-0156 "Class and Subtype existentials" begins now and runs through March 7, 2017. The proposal is available here:<br class=""><br class=""><a href="https://github.com/apple/swift-evolution/blob/master/proposals/0156-subclass-existentials.md" class="">https://github.com/apple/swift-evolution/blob/master/proposals/0156-subclass-existentials.md</a><br class="">Reviews are an important part of the Swift evolution process. All reviews should be sent to the swift-evolution mailing list at<br class=""><br class="">https://lists.swift.org/mailman/listinfo/swift-evolution<br class="">or, if you would like to keep your feedback private, directly to the review manager. When replying, please try to keep the proposal link at the top of the message:<br class=""><br class="">Proposal link:<br class=""><br class="">https://github.com/apple/swift-evolution/blob/master/proposals/0156-subclass-existentials.md<br class="">Reply text<br class=""><br class="">Other replies<br class="">What goes into a review?<br class=""><br class="">The goal of the review process is to improve the proposal under review through constructive criticism and, eventually, determine the direction of Swift. When writing your review, here are some questions you might want to answer in your review:<br class=""><br class=""><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>• What is your evaluation of the proposal?<br class=""></div><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 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 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 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>More information about the Swift evolution process is available at<br class=""><br class="">https://github.com/apple/swift-evolution/blob/master/process.md<br class="">Thank you,<br class=""><br class="">-Doug<br class=""><br class="">Review Manager<br class=""><br class="">_______________________________________________<br class="">swift-evolution mailing list<br class="">swift-evolution@swift.org<br class="">https://lists.swift.org/mailman/listinfo/swift-evolution<br class=""></blockquote><br class=""></div></body></html>