[Question] Can't figure out sealed class polymorphism with protobuf

Target code:

//@Polymorphic
@Serializable
sealed class Request {

    @Serializable
    @SerialName("StockHistory")
    data class StockHistory(
        @Polymorphic @Required val ticker: String,
        @Polymorphic @Required val hours: Int
    ) : Request()



    companion object {
        val protoBuf = ProtoBuf(SerializersModule {
            polymorphic(Request::class) {
                addSubclass(StockHistory.serializer())
            }
        })
    }
    
}

Main:

println(Request.protoBuf.load<Request>(Request.protoBuf.dump(Request.StockHistory("BTCs", 10))))

This results in this error: class kotlin.String is not registered for polymorphic serialization in the scope of class kotlin.String

I can’t seem to piece together what I’m doing wrong, I also tried doing this without the experimental “ImplicitReflectionSerializer” stuff, results in the same issue.

Any help is greatly appreciated.

[sandwwraith]

You need to remove @Polymorphic @Required from val ticker and hours, because you don’t want to serialize ticker and hours polymorphically, right? String always has one implementation, since it is a final class.

Also, correct form of dump would be Request.protoBuf.dump(Request.serializer(), Request.StockHistory("BTCs", 10)) (or dump<Request>(...)) – you need to use Request.serializer(), not Request.StockHistory.serializer(), since only the sealed class serializer knows about all hierarchy.

Unfortunately, due to #721 bug, you may experience java.lang.ArrayIndexOutOfBoundsException: 1 with a [funny] workaround of adding additional class. So final correct code would look like:

@Serializable
sealed class Request {

    @Serializable
    @SerialName("StockHistory")
    data class StockHistory(
        val ticker: String,
        val hours: Int
    ) : Request()

    @Serializable
    class Unused: Request()

    companion object {
        val protoBuf = ProtoBuf()
    }
}

println(Request.protoBuf.load<Request>(Request.protoBuf.dump<Request>(Request.StockHistory("BTCs", 10))))
// prints StockHistory(ticker=BTCs, hours=10)

[camdenorrb]

@sandwwraith Thank you so much! The array out of bounds exception really threw me off when I got it from experimenting. Glad this is all clear now.