<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 Apr 12, 2016, at 11:23 PM, David Hart 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=""><meta http-equiv="content-type" content="text/html; charset=utf-8" class=""><div dir="auto" class=""><div class="">I wouldn't mind driving the discussion and proposal, because I'd really like to see a more complete generics system. Before I start, can David or Doug, or someone else with a high-level view of the generics system tell me if this is where to start or if there is another feature in the Complete Generics manifesto which is more urgent first?</div></div></div></blockquote><div><br class=""></div><div>I think this is a fine feature to focus on. It’s useful, fits well in the system, and it’s scope is small enough that it’s achievable.</div><div><br class=""></div><span class="Apple-tab-span" style="white-space:pre"> </span>- Doug</div><div><br class=""><blockquote type="cite" class=""><div class=""><div dir="auto" class=""><div class=""><br class=""></div><div class="">David</div><div class=""><br class="">On 13 Apr 2016, at 01:46, Jacob Bandes-Storch via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""></div><blockquote type="cite" class=""><div class=""><div dir="ltr" class="">I'm interested, but I'm by no means claiming I'll have enough time to drive any of the discussion/proposal/implementation. :-(<div class="gmail_extra"><br clear="all" class=""><div class=""><div class="gmail_signature"><div dir="ltr" class=""><div class="">Jacob<br class=""></div></div></div></div>
<br class=""><div class="gmail_quote">On Tue, Apr 12, 2016 at 3:07 PM, Dave Abrahams via swift-evolution <span dir="ltr" class=""><<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5"><br class="">
on Tue Apr 12 2016, Douglas Gregor <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class="">
<br class="">
> On Apr 11, 2016, at 1:01 AM, Jacob Bandes-Storch via swift-evolution<br class="">
> <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class="">
><br class="">
> Doug wrote this in the Completing Generics manifesto, under "Minor<br class="">
> extensions":<br class="">
><br class="">
> *Arbitrary requirements in protocols<br class="">
><br class="">
> Currently, a new protocol can inherit from other protocols, introduce<br class="">
> new associated types, and add new conformance constraints to associated<br class="">
> types (by redeclaring an associated type from an inherited protocol).<br class="">
> However, one cannot express more general constraints. Building on the<br class="">
> example from “Recursive protocol constraints”, we really want the<br class="">
> element type of a Sequence’s SubSequence to be the same as the element<br class="">
> type of the Sequence, e.g.,<br class="">
><br class="">
> protocol Sequence {<br class="">
> associatedtype Iterator : IteratorProtocol<br class="">
> …<br class="">
> associatedtype SubSequence : Sequence where SubSequence.Iterator.Element<br class="">
> == Iterator.Element<br class="">
> }<br class="">
><br class="">
> +1.<br class="">
><br class="">
> To make it into Swift 3, would this feature require a proposal of its own?<br class="">
><br class="">
> Yes. Also, be wary that the syntax above potentially conflicts with the syntax<br class="">
> discussed as "moving the where clauses”:<br class="">
><br class="">
> <a href="http://thread.gmane.org/gmane.comp.lang.swift.evolution/13886/focus=14058" rel="noreferrer" target="_blank" class="">http://thread.gmane.org/gmane.comp.lang.swift.evolution/13886/focus=14058</a><br class="">
><br class="">
> How feasible would it be to implement on top of the current system?<br class="">
><br class="">
> Definitely! The archetype builder would need to learn to check these extra where<br class="">
> clauses, and one would need to be sure that the constraint solver is picking<br class="">
> them up as well.<br class="">
<br class="">
</div></div>By the way, having this would enable us to massively simplify the<br class="">
standard library, and potentially lots of user-written generic code,<br class="">
too. So I'm very excited that someone's interested!<br class="">
<span class="HOEnZb"><font color="#888888" class=""><br class="">
--<br class="">
Dave<br class="">
</font></span><div class="HOEnZb"><div class="h5"><br class="">
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