I have a question regarding registering subclasses...

# serialization

[Alvin Dizon]

I have a question regarding registering subclasses of a base class--so I have an abstract class that other response classes extend from and it looks similar to this:

@Serializable
abstract class BaseResponseV2<out T>(val success: Success<T>? = null)

@Serializable data class Success<out T>(val data: T? = null)

I usually register subclasses like this:

polymorphic(BaseResponseV2::class) {
   subclass(SomeResponse::class)
}

But I forgot to do so for the class below, but didn't encounter any crashes. Based on my understanding of https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/polymorphism.md#registered-subclasses and previous experiences, I should have gotten errors, but I'm puzzled as to why I didn't receive any for this particular case.

@Serializable class GetItemResponse : BaseResponseV2<GetItemResponseData>()

@Serializable
data class GetItemResponseData(val itemName: String? = null)

[glureau]

How did you serialize/deserialize?

[Alvin Dizon]

Alvin Dizon [5:48 PM]
I use this together with Retrofit:

private val serializerModule = SerializersModule {
        polymorphic(BaseResponseV2::class) {
            // subclasses go here
        }
    }    

private val jsonConfig = Json {
        ignoreUnknownKeys = true
        serializersModule = serializerModule
    }

    val serializationFactory =
        JsonConfig.asConverterFactory("application/json".toMediaType())

val retrofit = Retrofit.Builder()
            .client(okHttpClient)
            .baseUrl(BASE_URL)
            .addConverterFactory(serializationFactory)
            .build()
            .create(ItemService::class.java)

[glureau]

Can your post also your ItemService class?

[Alvin Dizon]

It should look similar to this:

interface ItemService {

    @GET("ItemService/getItem/v1") suspend fun getItem(): GetItemResponse
}

[glureau]

I was expecting a GetItemResponseData as the return type to be honest. But as it's reworked code I've some doubts 🙂 (like GetItemResponse is not abstract/open in your example, so there's no polymorphism here...)

[Alvin Dizon]

Hello, so what I'm getting is that GetItemResponse does not need to be registered like this:

polymorphic(BaseResponseV2::class) {
   subclass(GetItemResponse::class)
}

Even if it is a subclass of BaseResponseV2?