[swift-dev] Using Objective C class in Swift (open source, Linux)

[Joe Groff]

> On Feb 12, 2016, at 3:13 AM, Труб Илья via swift-dev <swift-dev at swift.org> wrote:
> 
> As Joe suggested, I try to build swiftc and libSwiftCore on linux with some OpenSource ObjC runtime. Now, I have successfully built swiftc, but when building Swift.o, it generates a lot of homogenous errorsl for example:
> 
> home/itrub/swift-root/swift/stdlib/public/core/ObjCMirrors.swift:23:45: error: argument type '_swift_shims_CFStringRef' (aka 'UnsafeMutablePointer<objc_object>') does not conform to expected type '_CocoaStringType' (aka 'AnyObject')
>  return _cocoaStringToSwiftString_NonASCII(theDescription)
>                                            ^~~~~~~~~~~~~~
> /home/itrub/swift-root/swift/stdlib/public/core/StringBridge.swift:27:54: error: cannot convert value of type '_CocoaStringType' (aka 'AnyObject') to expected argument type '_swift_shims_CFStringRef' (aka 'UnsafeMutablePointer<objc_object>')
>  let result = _swift_stdlib_CFStringCreateCopy(nil, source)
> 
> There are also other errors, but all of them concern with mutual convertation of AnyObject and UnsafeMutablePointer<objc_object> or UnsafeMutablePointer<U>. Could somebody hint me direction of further researches? What swift compiler code and existence of which Objc-runtime functions I have to check firstly? 
> 

The errors suggest that it isn't recognizing CFStringRef as a CoreFoundation type, and is just importing it as a plain 'struct objc_object*' pointer type. The C importer is tuned toward Apple's headers so might need a lot of tweaking to properly handle a different CF implementation. The bridging code in the standard library is generally pretty intimately tied to the Apple implementation of NSString/NSArray/NSDictionary, so you might want to disable it altogether in order to make progress on the core interop.

-Joe