At work, I just spent the last few weeks exploring and evaluating every format I could find, and my number one criteria was whether they supported sum types. I was especially interested in schema languages in which I could describe my types and then some standard specifies how to encode them using an on-the-wire format, usually JSON.
- Swagger represents sum types like Scala does, using subtyping. So you have a parent type
EitherIntStringwith two subtypesLeftandRightrepresented as{"discriminator": "Left", value: 42}and{"discriminator": "Right", value": "foo"}. Unfortunately, unlike in Scala in which the parent type is abstract and cannot be instantiated, in Swagger it looks like the parent type is concrete, so when you specify that your input is anEitherIntString, you might receive{"discriminator": "EitherIntString"}instead of one of its two subtypes. - JSON-schema supports unions, which isn't quite the same thing as sum types because