# arrow

Hey guys, what's the best way to deal with this error? Thanks

If Nel is not serializable you can create a custom serializer for it

https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/serializers.md

in the custom serializer part you can choose among multiple ways to solve it

We should support these things from a common module, but it probably belongs in a separate repository (?) 🤔 @Benoît you should be able to delegate to List.serializer

It can be a good idea to have an additional artifact with arrow serializers so we haven't to depend on serialization dependency on arrow as Simon said

Thanks to both of you for your answers, I was thinking of doing this manually yes, was just wondering first if there was an already existing NelSerializer somewhere that I had missed

for serialization of (not just) arrow datatypes I have this handy interface:

interface IsoSerializer<ENTITY, SURROGATE> : KSerializer<ENTITY> {

    val surrogateSerializer: KSerializer<SURROGATE>
    val iso: Iso<ENTITY, SURROGATE>

    override fun deserialize(decoder: Decoder): ENTITY =
        decoder.decodeSerializableValue(surrogateSerializer).let(iso::reverseGet)


    override val descriptor: SerialDescriptor
        get() = surrogateSerializer.descriptor

    override fun serialize(encoder: Encoder, value: ENTITY) {
        encoder.encodeSerializableValue(surrogateSerializer, iso.get(value))
    }

    companion object {
        inline operator fun <ENTITY, reified SURROGATE> invoke(
            iso: Iso<ENTITY, SURROGATE>,
            surrogateSerializer: KSerializer<SURROGATE>,
        ) = object : IsoSerializer<ENTITY, SURROGATE> {
            override val surrogateSerializer = surrogateSerializer
            override val iso = iso
        }
    }
}

here you can easily serialize anything by just providing a serializable surrogate type and an iso between your type and the surrogate

class NelSerializer<T>(elementSerializer: KSerializer<T>) :
    IsoSerializer<NonEmptyList<T>, List<T>> by IsoSerializer(Nel.listIso(),
        ListSerializer(elementSerializer))

fun <T> NonEmptyList.Companion.listIso(): Iso<NonEmptyList<T>, List<T>> = Iso(
    get = ::identity,
    reverseGet = { if (it is Nel<T>) it else Nel.fromListUnsafe(it) }
)

Amazing! Thanks a lot @than_