<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=""><div class="">I think there are two things going on here:</div><div class=""><br class=""></div><div class="">- The compiler allows a memory-corrupting cast, which should be rejected (a bug).</div><div class="">- But it's a useful thing to do (a language change).</div><div class=""><br class=""></div><div class="">I'm actually surprised about the bug, since we get plenty of questions about why the compiler doesn't allow it, implying that the compiler is indeed rejecting it. The answer is that protocol values and class values don't have the same representation, so converting between [Eatable] and [Burger] is an O(N) operation that requires allocating a new array. But that may not be a good enough reason not to allow it—conversions from NSArray to Array can do the same thing if the NSArray was mutable.</div><div class=""><br class=""></div><div class="">Jordan</div><div class=""><br class=""></div><br class=""><div><blockquote type="cite" class=""><div class="">On Feb 25, 2016, at 8:53 , Radosław Pietruszewski 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 style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Hey James,</div><div class=""><br class=""></div><div class="">The appropriate place for compiler bugs is <a href="https://bugs.swift.org/" class="">https://bugs.swift.org</a>, not Swift Evolution.</div><div class=""><br class=""></div>Best,<br class=""><div class="">
<div class="">— Radek</div>
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<br class=""><div class=""><blockquote type="cite" class=""><div class="">On 25 Feb 2016, at 17:44, James Campbell 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 dir="ltr" class="">Say I have been passed an array of objects that conform to a protocol called "Eatable" i.e [Eatable]<div class=""><br class=""></div><div class="">If I then try to cast them to an array of classes who happen to implement that protocol i.e [Burger]</div><div class=""><br class=""></div><div class="">The compiler lets me but in the runtime it corrupts the memory.</div><div class=""><div class=""><div class="gmail_signature"><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><p class=""><b class=""><font color="#cc0000" class="">___________________________________</font></b></p><p class=""><b class="">James⎥iOS Lead</b></p><p class=""><b class=""><font color="#cc0000" class=""><a href="mailto:james@supmenow.com" target="_blank" class="">james@supmenow.com</a>⎥<a href="http://supmenow.com/" target="_blank" class="">supmenow.com</a></font></b></p><p class=""><b class=""><font size="2" class="">Sup</font></b></p><p class=""><b class=""><font size="2" class="">Runway East
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