Hi everybody! I have a problem with with using Kot...

# serialization

[Oleh Havrysh]

Hi everybody!
I have a problem with with using Kotlin serialization for PersistentList
Since it doesn't support serialization I need to implement (or generate) it by myself

I went through docs but seems like it's not trivial case because it's both polymorphic (in my case in runtime I have SmallPersistentVector which is internal BTW) and generic (<E> forList items)

So what I have now:

class PersistentListSerializer<T>(elementSerializer: KSerializer<T>) : KSerializer<PersistentList<T>> {

    private val listSerializer = ListSerializer(elementSerializer)

    override val descriptor: SerialDescriptor = listSerializer.descriptor

    override fun serialize(encoder: Encoder, value: PersistentList<T>) {
        listSerializer.serialize(encoder, value)
    }

    override fun deserialize(decoder: Decoder): PersistentList<T> =
        listSerializer.deserialize(decoder).toPersistentList()
}

I'll have a lot of usages among the UI entities in my app (I use PersistentList for Compose), so wanted to define serializer in the single place where I save the state:

private val json = Json {
        serializersModule = SerializersModule {
            polymorphic(PersistentList::class) {
                subclass(SmallPersistentVector::class) // can't access since it's internal
            }

            contextual(PersistentList::class) { PersistentListSerializer(it.first()) } // doesn't work because in runtime it receives SmallPersistentVector, not PersistentList
        }
    }

[phldavies]

Rather than using a contextual, I found your serializer works fine either brought into the model as @file:UseSerializers(PersistentListSerializer::class) or @Serializable(with = PersistentListSerializer::class) on the property, or using typealias SerializablePersistentList<T> = @Serializable(with = PersistentListSerializer::class) PersistentList<T> as an example

[phldavies]

The typealias is probably the better option, unless you’re happy with remembering to specify the @file:UseSerializers(PersistentListSerializer::class) in file that defines a @Serializable class that uses PersistentList

[Oleh Havrysh]

@phldavies Thank you!
Yeah, the solution with typealias is good for me, now it works

[pdvrieze]

Also, to make things work correctly in all cases you may want to use a serialdescriptor with a new name (IIRC just call SerialDescriptor with the new name and base descriptor).