- Slow to compile
- Breaks compilers/doesn't have a stable ABI
- Optimizes poorly (at least, worse than GCC)
Swift I never used but I tried compiling it once and it was the bottom 2 slowest compiler I ever tested. The only thing nearly as bad was kotlin but 1) I don't actually remember which of these are worse 2) Kotlin wasn't meant to be a CLI compiler, it was meant to compile in the background as a language server so it was designed around that