Re: [RFC] [VOTE] Union types

> I'm personally against Union types because it makes no sense for classes I've been over this before but I'll repeat it here for completeness: this is not true. Unions provide a way to discriminate between potential sets of types. Even among classes there is power in unions. Consider the idea of encoding a Something or Nothing with methods such as map, flatmap, filter, etc. A Something will return a Something for map, and a Nothing will return a Nothing. By using inheritance there are two problems: 1. We can create additional subclasses that do not obey the semantics of the type. Imagine how frustrating a stack that does not behave like a stack would be; same principle here. 2. We don't have covariant return types so we cannot express that Nothing::map will return Nothing and Something::map will return Something. Using two final classes for Something and Nothing and then doing a union on them has neither of these downsides. Even if we add return type covariance we cannot solve problem 1. Given that there are numerous other uses with built-in types such as Array | Traversable (iterable), int | string (array key), int | float (numeric) and so forth it does not make sense to me to special case these things. Generality is better for language features than special casing.