Idiomatic Swift shouldn't really be using inheritance though, protocols (which support associatedtype, making varying errors types not an issue) are generally p

Idiomatic Swift shouldn't really be using inheritance though, protocols (which support associatedtype, making varying errors types not an issue) are generally preferred. Functions would be free to just "throws ErrorType" (probably the default for blank "throws", to avoid breaking backwards compatibility) if they really wanted to though, just like they can accept and return "Any", and the behavior would be identical to today. I prefer Result though, which just solves the problem of disjoint error types by using "mapError" and a sum type.