Comment by dwaite

They are different language designs sharing quite a few of the same features/philosophies.

Swift is good for business logic, like writing an app.

Rust is better for infrastructure, like writing a HTTP/3 server or Javascript VM.

Swift has an extremely good story about ABI stability, which makes sense when Apple ships a swift runtime and libraries as part of the OS, and needs the binaries to work across two dozen different major/minor releases.

Rust has up-front memory control primitives and options to remove the core library to cater to things like embedded systems development.

People have written apps in Rust, and Apple has written API backends and even device firmwares in Swift. I would argue both push against the ergonomics of the respective languages.