Is there any way for Jackson-style

As.PROPERTY

polymoprhic deserialization (e.g.,

{"type": "some.class.Name", "property": "value"}

instead of

["some.class.Name", {"property": "value"}]

) with kotlinx.serialization? I actually have some even more polymorphic gnarly (de)serailization requirements, which I could handle by some pretty ugly custom Jackson (de)serializers, but I would be interested a JVM-idependent solution. A key idea seems to be some kind of lookahead, during which Jackson can put tokens into a

TokenBuffer

while searching for the

"type"

attribute, and prefix the remaining token stream with the buffer contents upon calling the concrete deserializer. As the JSON schema I have to handle clearly wasn't designed with ease of parsing in mind, I have to rely a lot on lookahead. I am unsure how to achieve something similar with

KInput

and

KSerialClassDesc

.

Unfortunately there is no general mechanism for this for now (because in some formats lookahead is not possible), so this should be implemented directly in JSON. For now, you can create a custom serializer which will cast KInput to particular JsonInput and read values as json tree to map it later (like here: https://github.com/Kotlin/kotlinx.serialization/blob/master/runtime/jvm/src/test/kotlin/kotlinx/serialization/formats/json/JsonTreeAndMapperTest.kt#L35)

Thanks for the reply! That's unfortunate, but completely understandable. Guess I will end up sticking to Jackson in the immediate future.

@k_marussy I did two versions of this use case for demonstration purposes. One straightforward one and a more generic one. You can have a look at them here : https://gist.github.com/tokou/1660906bd103b0a68f2da283a9c6522c

Thanks! I think now I understand. Your example looks great -- my use case is a bit more complicated, but having access to a tree that I am still able to pass to generated parsers will help a lot.

Right I didn't think about that...

When I'll have a bit of time, I think I'll try to patch

JsonTreeMapper

and try out recursive polymorphic serialization that way.

Maybe this is just a lack of design, if you have feeling that `JsonTreeMapper.JsonTreeInput`should be public, feel free to submit a PR with fix and example.

In general, just making it public is insufficient. I am thinking more along the lines of something like this: https://github.com/Kotlin/kotlinx.serialization/pull/254