Custom polymorphic class discriminators.kt

@OptIn(ExperimentalSerializationApi::class)
@Serializable
@JsonClassDiscriminator("languageType")
sealed class Language {
    abstract val name: String
}

@Serializable
class Kotlin(override val name: String, private val version: String) : Language() {
    fun getFormattedVersion(): String {
        return version
    }
}

@Serializable
class Java(override val name: String) : Language()
/*
Result:

{
  "languageType":"Kotlin",
  "name":"Kotlin",
  "version":"1.5.30"
}
*/