3 ms·

Swift has Never, which is the return type of functions that don't terminate, such as fatalError(). https://developer.apple.com/documentation/swift/never https:

• Latty 6y ago
  As a use case other than the bottom type or "doesn't terminate", some pure languages use it to mean "this code path is impossible". I always liked the way Elm (and I assume many other pure functional languages) define(s) `Never`: type Never = JustOneMore Never As the only constructor takes an instance of itself as an argument, any attempt to construct one would become infinite. This very naturally allows for a function to obtain any value you want: never : Never -> a never (JustOneMore nvr) = never nvr If you can get a `Never` instance that can't possibly exist, you must be in a code path that can't happen, so you can get any value you want to short circuit early and make impossible return values. That makes it very useful in a language with no runtime exceptions to handle impossible cases. (E.g: you can go from a `Result Never a` to an `a` where normally you'd have to handle the error case). [1]: https://github.com/elm/core/blob/1.0.5/src/Basics.elm#L948 https://github.com/elm/core/blob/1.0.5/src/Basics.elm#L948