I have a class `Foo<Self>` and `Foo#seriali...

# serialization

[Eric Ou]

I have a class Foo<Self> and Foo#serializer: KSerializer<Self>, but when I try to serialize it, it says: Star projection isn't allowed, so instead of

abstract class Foo<Self: Foo<Self>> {
    abstract val serializer: KSerializer<Self>
}

@OptIn(ExperimentalSerializationApi::class)
val module = SerializersModule {
    polymorphicDefaultSerializer(Foo::class) {
        it.serializer as KSerializer<Foo>
    }
}

I have to do

abstract class Foo<Self: Foo<Self>>: SerializableFoo {
    abstract val serializer: KSerializer<Self>

    override val s
        get() = serializer
}

interface SerializableFoo {
    val s: KSerializer<*>
}

@OptIn(ExperimentalSerializationApi::class)
val module = SerializersModule {
    polymorphicDefaultSerializer(SerializableFoo::class) {
        it.s as KSerializer<SerializableFoo>
    }
}

And always call

Json.encodeToString<SerializableFoo>(foo)

Which is much less clean, is there a workaround to tell it to ignore the <*> and "just move on"?

[ephemient]

https://github.com/Kotlin/kotlinx.serialization/issues/607?

[ephemient]

also it seems very unusual to have serializer on each instance… how could deserialization possibly work

[ephemient]

you can get around the module with

abstract class Foo<Self : Foo<Self>> {
    abstract val serializer: KSerializer<Self>

    @ExperimentalSerializationApi
    @InternalSerializationApi
    object Serializer : SerializationStrategy<Foo<*>> {
        override val descriptor: SerialDescriptor =
            buildSerialDescriptor(Foo::class.qualifiedName!!, PolymorphicKind.OPEN)

        @Suppress("UNCHECKED_CAST")
        override fun serialize(encoder: Encoder, value: Foo<*>) {
            encoder.encodeSerializableValue(value.serializer as SerializationStrategy<Foo<*>>, value)
        }
    }
}

@Serializable
class FooImpl : Foo<FooImpl>() {
    override val serializer: KSerializer<FooImpl>
        get() = serializer()
}

@OptIn(ExperimentalSerializationApi::class, InternalSerializationApi::class)
fun main() {
    println(Json.encodeToString(Foo.Serializer, FooImpl()))
}