SwiftUI relies on implicit return statements, property wrappers, keypath member lookup and function builders. All but the last have gone through the evolution process and are implemented completely in Swift 5.1. The function builders feature has been pitched and is going through the process; the current implementation uses an underscored attribute. The implementation might change but it will not affect client code, only the declarations of the relevant types in SwiftUI. This means you can’t define your own function builders today without a future compiler possibly breaking source compatibility with your implementation — but other than that there’s no magic in the SwiftUI API beyond the language itself.