The important sentence is: "Obviously it would be nicer if Scala supported union types as primitives, but at least this construction shows that the Scala compi

The important sentence is: "Obviously it would be nicer if Scala supported union types as primitives, but at least this construction shows that the Scala compiler has all the information it needs to be able to do that. " Which means the compiler can do this but need syntactic sugar to make it more accessible.