<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 4, 2016, at 9:54 PM, Russ Bishop 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=""><blockquote type="cite" 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="Apple-interchange-newline">On Apr 4, 2016, at 9:22 PM, Brent Royal-Gordon via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""><blockquote type="cite" class=""><span class="Apple-tab-span" style="white-space: pre;"> </span><a href="https://github.com/apple/swift-evolution/blob/master/proposals/0058-objectivecbridgeable.md" class="">https://github.com/apple/swift-evolution/blob/master/proposals/0058-objectivecbridgeable.md</a><br class=""></blockquote><br class="">There are a number of things I'm not really clear on.<br class=""><br class="">* * *<br class=""><br class="">Consider this Objective-C API:<br class=""><br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>ObjCFizzer* myFizzer;<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 myFizzer: ObjCFizzer<br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>var myFizzer: Fizzer<br class=""></blockquote><br 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=""><span 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;" class="">The latter. The idea is that the importer sees the bridged type is available and substitutes it on all imported signatures. The actual mechanics of that will involve some generated code (thunk) to call the protocol. I could update the proposal to include what the body of that thunk might look like but it didn’t seem terribly interesting.</span><br 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=""></div></blockquote><div><br class=""></div><div>Right. There will be some thunking the compiler does.</div><br class=""><blockquote type="cite" class=""><div class=""><blockquote type="cite" 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="">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 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=""><span 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;" class="">The intention there is that it imports as the bridged type so the latter.</span><br 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=""></div></blockquote><div><br class=""></div><div>I disagree here: ObjCFizzer is bridged, not ObjCMutableFizzer, so it would be the former.</div><br class=""><blockquote type="cite" class=""><div class=""><br 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 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" 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="">On the basis of NSArray and friends, I assume they come across like this:<br class=""><br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>var myFizzer: Fizzer<br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>var myMutableFizzer: ObjCMutableFizzer<br class=""><br class="">Is that correct?<br class=""></blockquote><br 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=""><span 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;" class="">No</span><br 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=""></div></blockquote><div><br class=""></div>I would have said “yes" ;)</div><div><br class=""></div><div><blockquote type="cite" class=""><div class=""><blockquote type="cite" 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="">* * *<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 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=""><span 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;" class="">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 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=""></div></blockquote><div><br class=""></div><div>We can bridge from, e.g., Fizzer to ObjCFizzer via “as Fizzer” using the entry-point</div><div><br class=""></div><div><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 style="color: rgb(51, 51, 51); font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; background-color: rgb(247, 247, 247);" class=""> </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 style="color: rgb(51, 51, 51); font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; background-color: rgb(247, 247, 247);" class="">() </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 style="color: rgb(51, 51, 51); font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; background-color: rgb(247, 247, 247);" class=""> ObjectiveCType</span></div><div class=""><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><span 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;" class="">For bridging an Objective-C library into Swift, ideally all the APIs will be annotated with SWIFT_BRIDGED so on import the Swift code won’t even be aware the Objective-C type exists. All you’ll see in Swift is the appropriate Swift types. This gives a library (say Photos.framework or UIKit) the chance to provide truly native Swift types by shipping a module with combined Swift and Objective-C code.</span><br 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 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=""><span 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;" class="">Similarly, going the other direction (an app with Objective-C and Swift code) this proposal eliminates the need to deal with the Objective-C types in Swift.</span><br 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=""></div></blockquote><div><br class=""></div>The ObjC types will still exist (unless explicitly banned via NS_UNAVAILABLE_IN_SWIFT or similar), and can leak through in some cases (e.g., UnsafeMutablePointer<ObjCFuzzer>).<br class=""><div><br class=""></div></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- Doug</div><div class=""><br class=""></div></body></html>