Support multiple class descriminators for polymorphism.

What is your use-case and why do you need this feature? As of writing this issue, only a single classDiscriminator can be specified on a Json object. I’m working with a REST api where for different endpoints or error codes, the object returned will use a different “class discriminator”.

For example, if the response code is != 200, then an error in form of JSON is returned.

The discriminator here is errcode.

sealed class MatrixError : Throwable() {
    abstract val errcode: String
}

@Serializable
@SerialName("M_NOT_FOUND")
data class NotFound(override val error: String) : MatrixError() {
    override val errcode get() = "M_NOT_FOUND"
}

@Serializable
@SerialName("M_LIMIT_EXCEEDED")
data class LimitExceeded(
    override val error: String,

    @SerialName("retry_after_ms")
    val retryAfterMillis: Long
) : MatrixError() {
    override val errcode get() = "M_LIMIT_EXCEEDED"
}

If the response code is 200, then the model uses type as the discriminator.

sealed class Event

@SerialName("m.room")
data class RoomEvent : Event

@SerialName("m.join")
data class JoinEvent(val userId: String) : Event

Describe the solution you’d like I would like to be able to annotate the parent class with a discriminator.

Or supply a class discriminator in the module like so.

SerializersModule {
    polymorphic<MatrixError>(discriminator="errcode") {
        addSubclass(MatrixError.Unknown.serializer())
        addSubclass(MatrixError.NotFound.serializer())
        addSubclass(MatrixError.Forbidden.serializer())
        addSubclass(MatrixError.UnsupportedRoomVersion.serializer())
        addSubclass(MatrixError.LimitExceeded.serializer())
   }
}

[kroegerama]

Will this be included in the next release? I’m really looking forward to it.

[sandwwraith]

@KamilJanda It is planned and in progress now