Actually we're just talking about two different ways to represent the same concept. In the ML-derived languages, which traditionally did not have first-class union types - which I assume derives from the fact that they don't have _subtyping_, the workaround for representing A|B is to create an algebraic sum type Either which wraps the actual value we're interested in. For the case of null|B, there's a specialized Maybe or Option type.

Now, this pattern has recently been imported into object-oriented land by languages like Scala and now Java 8, because these languages also don't have first-class union types.

But in my opinion, that's the wrong path to have taken. In OO-land, we _do_ have subtyping, so things like unions and intersections are well-representable within the type system, and we don't need these workaround wrapper types.

I don't understand the difference, and a quick search turned up nothing. Care to educate?