Thanks–your not only did you method work, it had the side effect of obviating the need for a Bridging Header. One more thing: what happens if self isn’t a Bar (crash, I’m guessing)? Is there a way to compare the type of self, other than using `is` (which has the same issue as unsafeBitCast in that I don’t have the declaration for it)?
Saagar Jha > On Feb 4, 2017, at 4:02 PM, Dave Abrahams via swift-users > <swift-users@swift.org> wrote: > > > on Fri Feb 03 2017, Saagar Jha <swift-users-AT-swift.org > <http://swift-users-at-swift.org/>> wrote: > >> Hello, >> >> I’m having an issue migrating some old Objective-C code that looks like this: >> >> @implementation Foo >> >> - (void)load { >> // Swizzle one of Bar’s methods to call Foo’s baz method >> } >> >> - (void)baz { >> [self baz]; >> if ([self isKindOfClass:NSClassFromString(@“Bar”)]) { >> Bar *bar = (Bar *)self; // I can’t migrate this >> // work with bar >> } >> } >> >> @end >> >> I’m trying to cast self to a Bar at runtime, and use it to call Bar’s >> methods. Sounds like an easy >> to task for unsafeBitCast, right? The issue is that I don’t have access to >> the implementation of >> Bar’s class at compile time (this is a plugin, so it’s loaded by another >> application which contains >> Bar). In Objective-C I can create a header and stick a dummy interface for >> Bar in it; the cast will >> work if Bar exists at runtime. However, in Swift, unsafeBitCast requires me >> to use Bar.self, which >> does not exist. Is there any way to get this cast to work? > > Bar.self exists if you have a declaration of it exposed to swift, which > would be required for all the “work with bar” code above. If you don't > have Bar.self, it's because there's no declaration visible to your Swift > code. My usual workaround would be to declare an @objc protocol having > the bar APIs you want to use, and then cast self to an instance of that > @objc protocol. The right way to do that is by using > UnsafePointer.withMemoryRebound(to: ), e.g. > > var mutableSelf = self // can't get pointer to immutable value > withUnsafePointer(to: &mutableSelf) { selfPtr in > selfPtr.withMemoryRebound(to: BarProtocol, capacity: 1) { barPtr in > let bar = barPtr.pointee > // work with bar > } > } > > HTH, > > -- > -Dave > > _______________________________________________ > swift-users mailing list > swift-users@swift.org <mailto:swift-users@swift.org> > https://lists.swift.org/mailman/listinfo/swift-users > <https://lists.swift.org/mailman/listinfo/swift-users>
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