Comment by zozbot234

Or they were just willing to accept a significant increase in language complexity, to deal with things that Rust just punts on by basically expecting you to stick to #[repr(C)] at your preferred dylib boundary. (Though, potentially, that #[repr(C)] could become e.g. #[repr(SomeArbitraryStableABI)], and there have been proposals to this effect.) And they did this precisely because of that perception that Swift "wouldn't be usable" otherwise.