<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 May 12, 2016, at 18:34, Andrew Trick <<a href="mailto:atrick@apple.com" class="">atrick@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><div class=""><blockquote type="cite" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class=""><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">- On the flip side, I think we <i class="">do</i> need to preserve the ability to reference-cast in order to send Objective-C messages, at least for now. I don’t know how I want to expose that to users, though. (In general it’s probably worth seeing how unsafeBitCast is used in the wild and what we’d recommend instead.)</div></div></blockquote><br class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"></div><div class=""><div class="">Does ``X as Y`` fail for some reason? We have unchecked versions of ``X as Y`` for performance reasons: ``unsafeDowncast`` and ``_unsafeReferenceCast``.</div></div></div></div></div></blockquote></div><div class=""><br class=""></div><div class="">The particular case I’m thinking about is where we reinterpret an AnyObject as an @objc protocol because we don’t know the dynamic type we would need to add a method to. This doesn’t happen much, and maybe we just say sending arbitrary messages requires an ObjC-side workaround. Or we commit to ‘_unsafeReferenceCast’ and de-underscore it.</div><div class=""><br class=""></div><div class="">(_unsafeReferenceCast is probably a better choice for StdlibUnittest, which is where I used this.)</div><div class=""><br class=""></div><div class="">Jordan</div></body></html>