There's a fun thing like this in Swift too! `Void` is an empty tuple, and has all of the related constraints (can't conform to protocols, being the most salient one). If you have a type that has to conform to, say, `Equatable` or `Codable` you should instead use `Never?` which you can conform to most protocols via throwing `fatalError` on an extension of `Never` to the protocol.

Anyway, I write basically this on my blog for a more thorough explanation: https://www.jackyoustra.com/blog/non-equatable-void