<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 5, 2016, at 11:36 AM, Russ Bishop <<a href="mailto:xenadu@gmail.com" class="">xenadu@gmail.com</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=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Apr 5, 2016, at 10:14 AM, Douglas Gregor <<a href="mailto:dgregor@apple.com" class="">dgregor@apple.com</a>> wrote:</div><div class=""><div 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;" class=""><blockquote type="cite" class=""><div class=""><br class=""></div></blockquote><blockquote type="cite" 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;">Suppose there is also a subclass (say, ObjCMutableFizzer), and we have this Objective-C API:<br class=""><br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>ObjCMutableFizzer* mutableFizzer;<br class=""><br class="">Which of these represents how it is imported?<br class=""><br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>var myMutableFizzer: ObjCMutableFizzer<br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>var myMutableFizzer: Fizzer<br class=""></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;"><span 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; float: none; display: inline !important;">The intention there is that it imports as the bridged type so the latter.</span><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></blockquote><div class=""><br class=""></div><div class="">I disagree here: ObjCFizzer is bridged, not ObjCMutableFizzer, so it would be the former.</div><br class=""></div></div></blockquote><div class=""><br class=""></div><div class="">Hmmm… So all subclasses are hidden as far as the interface is concerned (and the ambiguity rules)? I’m fine with that, it seems like it suites the class cluster approach just fine.</div></div></div></div></blockquote><div><br class=""></div><div>Not “hidden”; they’re accessible and not bridged.</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><blockquote type="cite" class=""><div 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;" class=""><br class=""></div><div 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;" class=""><blockquote type="cite" 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;"><br class="">* * *<br class=""><br class="">Foundation classes can sometimes be bridged using an upcast (a plain `as`), which cannot crash. Is this possible with ObjectiveCBridgeable? If so, how? If not, will Foundation classes lose that ability?<br class=""><br class="">If this feature can't be expressed with ObjectiveCBridgeable, is this seen as a shortcoming we should try to overcome, or the proper design? I worry about the unnecessary proliferation of exclamation points, especially since many style guides strongly discourage them, which will turn this into an unnecessary proliferation of unnecessary `if let`s.<br class=""></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;"><span 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; float: none; display: inline !important;">This would not be possible. This sort of bridging only works with special magic types because they are known to always succeed. There is no condition under which Swift will fail to convert String to NSString. The compiler/runtime can’t prove that about any arbitrary type.</span><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></blockquote><div class=""><br class=""></div><div class="">We can bridge from, e.g., Fizzer to ObjCFizzer via “as Fizzer” using the entry-point</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span><span class="pl-k" style="font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; background-color: rgb(247, 247, 247); box-sizing: border-box; color: rgb(167, 29, 93);">func</span><span class="" style="color: rgb(51, 51, 51); font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; background-color: rgb(247, 247, 247);"><span class="Apple-converted-space"> </span></span><span class="pl-en" style="font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; background-color: rgb(247, 247, 247); box-sizing: border-box; color: rgb(121, 93, 163);">bridgeToObjectiveC</span><span class="" style="color: rgb(51, 51, 51); font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; background-color: rgb(247, 247, 247);">()<span class="Apple-converted-space"> </span></span><span class="pl-k" style="font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; background-color: rgb(247, 247, 247); box-sizing: border-box; color: rgb(167, 29, 93);">-></span><span class="" style="color: rgb(51, 51, 51); font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; background-color: rgb(247, 247, 247);"><span class="Apple-converted-space"> </span>ObjectiveCType</span></div><div class=""><br class=""></div></div></blockquote><div class=""><br class=""></div><div class="">It does seem strange that this is asymmetrical but I don’t know that it is worth the complexity to introduce an extended protocol to declare a type has a bi-directional always-succeeds bridging conversion.</div></div></div></div></blockquote><div><br class=""></div><div>It is a little odd; we have isBridgedToObjectiveC and bridgeToObjectiveC, where we could possibly have the latter produce an ObjectiveCType? and remove the former.</div></div><br class=""><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- Doug</div><div class=""><br class=""></div></body></html>