<div><br><div class="gmail_quote"><div>On Fri, Jun 23, 2017 at 17:59 Mike Kluev via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div>On 23 June 2017 at 23:18, Tony Allevato <span><<a href="mailto:tony.allevato@gmail.com" target="_blank">tony.allevato@gmail.com</a>></span> wrote:</div><div><div><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-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div><div class="gmail_quote"><div>class C1: C2 ==> C1() is C2 == true</div><div>class C1: P ==> C1() is P == true</div><div>class C1: S ==> C1() is S == false?</div></div></div></blockquote><div><br></div></div></div></div></div><div><div><div class="gmail_extra"><div class="gmail_quote"><div>ok. changing the rule then:</div><div><br></div><div>C() is S == true</div><div><br></div><div><div><div>foo(x) acts the same way as foo(x.super)</div><div>bar(&x) acts the same way as bar(&x.super)</div></div></div><div><br></div><div>i am not quite sure i am getting the answers along the lines of "use protocol forwarding" instead. i have no protocol to begin with. for a preexisting value type (e.g. OS provided)</div></div></div></div></div></blockquote><div><br></div><div>Value subtyping has many uses and is something which will be very powerful, if and when it arrives in Swift. The idea of a reference type that can subtype a value type is intriguing but obviously requires a lot of thought. Certainly, it is something far into the future.</div><div><br></div><div>However, *even at that time*, I'm quite certain that you will not be able to subtype an OS-provided value type unless it has already been designed for subtyping, just as you are not able to subtype Swift-native reference types unless they are already designed for subtyping. At that time, just as now, the way to accomplish what you wish for would be some sort of forwarding. The difficulty of maintains a third-party protocol for core types should be much alleviated with greater API stability.</div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div><div class="gmail_extra"><div class="gmail_quote"><div> it would be a nightmare to create and maintain the corresponding protocol.</div></div></div></div></div><div><div><div class="gmail_extra"><div class="gmail_quote"><div><br></div><div>Mike<br></div><div><br></div></div></div></div></div>
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