Migrate from Objective-C++ to pure Swift

[alex-vasenin]

Swift 5.9 introduced direct interoperability with C++ without relying on Objective-C as a bridge. That means that we can get rid of Objective-C wrappers and improve performance a bit. Backward compatibility isn't much of problem, since starting from 29.04.2024 apps uploaded to the App Store must be build with Xcode 15.

[alex-vasenin]

I tried to port CAARiseTransitSet2 to SwiftAA using native C++ interoperability and I think it's not ready for production.

First, at the moment if one of your dependencies needs cxx-interop you must enable it for entire project (see swiftlang/swift#66156).

Second, enabling cxx-interop for existing project is potentially a code-breaking change. Specifically, in SwiftAA I have to make one testing function which returns Never private because it produces an error in generated SwiftAA-Swift.h file. Another similar error in this file is that compiler can't find definitions of UIColor/NSColor and CLLocation classes (I have to resort to ObjC-style forward-declaring them in one of the header, but it didn't work on the client).

And the third thing is enabling cxx-interop increases compilation duration 3-4 times. Considering one have to enable interop for entire project it's a deal breaker.

The results are here (it's not finished, some headers and ObjC forward declarations are missing from produced framework)

I hope the situation will improve in future.