How to create a serializer for a recursive map? Just like `class A : Map<String, A>` . The map...

# serialization

[Settingdust]

How to create a serializer for a recursive map? Just like class A : Map<String, A> . The map is guava multimap that not implement the map interface. But can be converted to a map.
Below is what I tried. Will throw StackOverflowError from SetSerializer

object Serializer : KSerializer<A> {
    private val serializer by lazy { MapSerializer(String.serializer(), SetSerializer(this)) }
    override val descriptor by lazy {
        SerialDescriptor(
            "A",
            serializer.descriptor
        )
    }
    override fun deserialize(decoder: Decoder) =
        A(Multimaps.newMultimap(serializer.deserialize(decoder)) { setOf() })
    override fun serialize(encoder: Encoder, value: A) =
        serializer.serialize(encoder, value.asMap().mapValues { it.value.toSet() })
}

[ephemient]

I don't think that's actually what you want to represent a multimap

[ephemient]

as Multimap<K, V> ≅ Map<K, Collection<V>> that would seem to be a better way to represent it

[ephemient]

class MultimapSerializer<K, V>(
    keySerializer: KSerializer<K>,
    valueSerializer: KSerializer<V>,
) : KSerializer<Multimap<K, V>> {
    private val surrogateSerializer = MapSerializer(keySerializer, ListSerializer(valueSerializer))
    override val descriptor = SerialDescriptor("com.google.common.collect.Multimap", surrogateSerializer.descriptor)
    override fun serialize(encoder: Encoder, value: Multimap<K, V>) {
        encoder.encodeSerializableValue(surrogateSerializer, value.asMap().mapValues { it.value.toList() })
    }
    override fun deserialize(decoder: Decoder): Multimap<K, V> {
        return Multimaps.newListMultimap(decoder.decodeSerializableValue(surrogateSerializer), ::ArrayList)
    }
}

[ephemient]

another representation is that Multimap<K, V> ≅ Collection<Map.Entry<K, V>>, so this would be an option as well

class MultimapSerializer<K, V>(
    keySerializer: KSerializer<K>,
    valueSerializer: KSerializer<V>,
) : KSerializer<Multimap<K, V>> {
    private val surrogateSerializer = ListSerializer(MapEntrySerializer(keySerializer, valueSerializer))
    override val descriptor = SerialDescriptor("com.google.common.collect.Multimap", surrogateSerializer.descriptor)
    override fun serialize(encoder: Encoder, value: Multimap<K, V>) {
        encoder.encodeSerializableValue(surrogateSerializer, value.entries().toList())
    }
    override fun deserialize(decoder: Decoder): Multimap<K, V> {
        return ImmutableListMultimap.copyOf(decoder.decodeSerializableValue(surrogateSerializer))
    }
}

depending on which representation you prefer

[Settingdust]

What's the different of set and list?
The problem is the cyclic dependencies. I've found the JsonElementSerializer is using a function named defer for this. But the element descriptor in my case is fetch from a SetSerializer , I don't know how to defer that

Edit: It's fine now. With the defer of the descriptor of MapSerializer