This is great news!

I was also kind of surprised to see the article talking about algebraic data types... table stakes for ADTs is sum types and I have missed them considerably in the Java ecosystem.

Kotlin has something like them with sealed classes, although I'm a newcomer to the Kotlin and Spring Boot ecosystem so I don't see explicitly how I make some simple case like JSON

    {"type": "left", "abc": 123}
    {"type": "right", "def": "456"}

turn into some structure like:

    sealed class EitherTest {
        data class Left(val abc: Long): EitherTest()
        data class Right(val def: String): EitherTest()
    }

rather than the hacky version that you have to do in relational databases and Java which don't support such things,

    enum class EitherType { LEFT, RIGHT }
    data class EitherTest(val type: EitherType, val abc: Int?, val def: String?)

Like I’m not saying that there’s no way, I’m sure there’s a way... just that the ecosystem seems so hesitant to embrace sum types that like the above sealed class is widely viewed as a hack and there is no statement about “here is how you actually use sum types for everything in your Spring application with Kotlin.”

Was gonna give the choose-your-own-adventure example of why sum types are handy and how you have to kind of hack around them with inheritance when you don't have them but it occurs to me that anyone who has stuck with this comment this far probably already has some familiarity with this?