Sounds similar to how you need to do Some(x) when passing x to something expecting an Option in rust.

Swift interestingly doesn’t require this, but only because Optionals are granted lots of extra syntax sugar in the language. It’s really wrapping it in .some(x) for you behind the scenes, but the compiler can figure this out on its own.

This means that in swift, changing a function from f(T) to f(T?) (ie. f(Optional<T>)) is a source-compatible change, albeit not an ABI-compatible one.