Kotlinx Serialization, inlining sealed class/interface [duplicate] - kotlin

Question

This question already has an answer here:
kotlinx deserialization: different types && scalar && arrays
(1 answer)
Closed 7 months ago.
With a structure similar to the following:
#Serializable
sealed class Parameters
#Serializable
data class StringContainer(val value: String): Parameters()
#Serializable
data class IntContainer(val value: Int): Parameters()
#Serializable
data class MapContainer(val value: Map<String, Parameters>): Parameters()
// more such as list, bool and other fairly (in the context) straight forward types
And the following container class:
#Serializable
data class PluginConfiguration(
// other value
val parameters: Parameters.MapContainer,
)
I want to reach a (de)serialization where the paramters are configured as a flexible json (or other) map, as one would usually expect:
{
"parameters": {
"key1": "String value",
"key2": 12,
"key3": {}
}
}
And so on. Effectively creating a flexible structure that is still structured enough to not be completely uncontrolled as Any would be. There's a fairly clearly defined (de)serialization, but I cannot figure how to do this.
I've tried reading the following
https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/serialization-guide.md
And I do have a hunch that a polymorphic serializer is needed, but so far I'm bumping in to either generic structures, which I believe is way overkill for my purpose or that it for some reason cannot find the serializer for my subclasses, when writing a custom serializer for Parameters.
Update
So using custom serializers combined with surrogate classes, most things are working. The current problem is when values are put into the map, I get a kotlin.IllegalStateException: Primitives cannot be serialized polymorphically with 'type' parameter. You can use 'JsonBuilder.useArrayPolymorphism' instead. Even when I enable array polymorphism this error arises

Answer 1

The answer with kotlinx deserialization: different types && scalar && arrays is basically the answer, and the one I will accept. However, for future use, the complete code to my solution is as follows:
Class hierarchy
#kotlinx.serialization.Serializable(with = ParametersSerializer::class)
sealed interface Parameters
#kotlinx.serialization.Serializable(with = IntContainerSerializer::class)
data class IntContainer(
val value: Int
) : Parameters
#kotlinx.serialization.Serializable(with = StringContainerSerializer::class)
data class StringContainer(
val value: String
) : Parameters
#kotlinx.serialization.Serializable(with = MapContainerSerializer::class)
data class MapContainer(
val value: Map<String, Parameters>
) : Parameters
#kotlinx.serialization.Serializable
data class PluginConfiguration(
val plugin: String,
val parameters: MenuRunnerTest.MapContainer
)
Serializers:
abstract class BaseParametersSerializer<T : Parameters> : KSerializer<T> {
override val descriptor: SerialDescriptor = JsonElement.serializer().descriptor
override fun serialize(encoder: Encoder, value: T) {
fun toJsonElement(value: Parameters): JsonElement = when (value) {
is IntContainer -> JsonPrimitive(value.value)
is MapContainer -> JsonObject(
value.value.mapValues { toJsonElement(it.value) }
)
is StringContainer -> JsonPrimitive(value.value)
}
val sur = toJsonElement(value)
encoder.encodeSerializableValue(JsonElement.serializer(), sur)
}
override fun deserialize(decoder: Decoder): T {
with(decoder as JsonDecoder) {
val jsonElement = decodeJsonElement()
return deserializeJson(jsonElement)
}
}
abstract fun deserializeJson(jsonElement: JsonElement): T
}
object ParametersSerializer : BaseParametersSerializer<Parameters>() {
override fun deserializeJson(jsonElement: JsonElement): Parameters {
return when(jsonElement) {
is JsonPrimitive -> when {
jsonElement.isString -> StringContainerSerializer.deserializeJson(jsonElement)
else -> IntContainerSerializer.deserializeJson(jsonElement)
}
is JsonObject -> MapContainerSerializer.deserializeJson(jsonElement)
else -> throw IllegalArgumentException("Only ints, strings and strings are allowed here")
}
}
}
object StringContainerSerializer : BaseParametersSerializer<StringContainer>() {
override fun deserializeJson(jsonElement: JsonElement): StringContainer {
return when(jsonElement) {
is JsonPrimitive -> StringContainer(jsonElement.content)
else -> throw IllegalArgumentException("Only strings are allowed here")
}
}
}
object IntContainerSerializer : BaseParametersSerializer<IntContainer>() {
override fun deserializeJson(jsonElement: JsonElement): IntContainer {
return when (jsonElement) {
is JsonPrimitive -> IntContainer(jsonElement.int)
else -> throw IllegalArgumentException("Only ints are allowed here")
}
}
}
object MapContainerSerializer : BaseParametersSerializer<MapContainer>() {
override fun deserializeJson(jsonElement: JsonElement): MapContainer {
return when (jsonElement) {
is JsonObject -> MapContainer(jsonElement.mapValues { ParametersSerializer.deserializeJson(it.value) })
else -> throw IllegalArgumentException("Only maps are allowed here")
}
}
}
This structure should be expandable for lists, doubles and other structures, not included in the example :)