I definitely need a tooling ecosystem, so I'll be waiting for good integration between IDEs and LLVM for Swift. Maybe Atom or VSCode will get there soon. For libraries, when I really need something, I'll wrap it myself using C FFI. It is very easy to pass C structs by value or reference between Julia and C. Go is not bad either and does a lot of static checking for me. Swift sounds like for value types it should be easy. Java is super painful with the marshalling back and forth.