[CodeWithCoffee]

Furthermore, Apple did bring up a slide during the Platform State of the Uniform (slide 56 in the PDF) saying source compatibility wouldn't be guaranteed (but that converters would be provided) because the language will evolve. I can't imagine that they'll introduce dramatic changes that will break code generated by PaintCode, but it would be a pain if you have to completely regenerate your all rendering code with each update to Xcode/Swift.

[Someone]

I haven't listened to that presentation or read the PDF, but from what I read about it I would bet that 'evolve' refers more to the time until the official release than to the time after that. Of course the language will evolve, but it will be slower and shouldn't do so in incompatible ways.

Until official release, though, Apple may make huge breaking changes (change keywords, tweak the grammar, maybe drop a feature or two. For example, do we really need trap on overflow for integers in what, in the end, is a compiled language?)