Though Swift's `if let` is AFAIK hardcoded to their built-in optional type, whereas when Rust lifted the idea they made it work with any enum. I believe Swift recently gained `if case let` as an equivalent to how `if let` works in Rust.
It was new in Swift 2 I think. Didn't use it yet. But it's basically a single case statement lifted from switch, nothing more. But enums and switch statements can be really complex beasts by themselves in Swift.
If Rust only allows it on enums that would be extremely weird.
In a switch statement I sometimes want to switch on the object, then see if I'm allowed to unwrap it to a certain class and immediately use it afterwards. Useful for parsing an array of mixed object types that should be processed differently.
But I honestly think Swift allows people to write elaborate illegible codegolf-y bullshit sometimes. Sometimes the Swift compiler still chokes on too complex expressions and you need to add some explicit types or separate out in several statements what you were trying to do in one statement. Usually a good warning that your code is hard to read even by humans.
If-let can be used with refutable patterns (the refutation/counterexample to the pattern is when the else case runs). Irrefutable patterns can be used with regular let.
