Is or will it be possible to write a serializer for `Map<String, (Number|Boolean|String)?>` , ...

# serialization

[pniederw]

Is or will it be possible to write a serializer for Map<String, (Number|Boolean|String)?> , ideally in a serialization format agnostic way? I guess what I'm asking for is Decoder.peekType(). I've looked at JsonDecoder.decodeJsonElement() but the implementation is all internal.

[ephemient]

use a Map<String, JsonPrimitive> or something as a surrogate maybe? https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/serializers.md#composite-serializer-via-surrogate

[Nikky]

do you want union type in the serialized thing ?
or just support either one of them with a single serializer ?

[pniederw]

@ephemient That's my current workaround, but I'd rather not convert the input to JsonElement (in fact I need to support nested lists and maps too) and I want this to be serialization format agnostic.

[ephemient]

JsonPrinitive there will serialize like any other sealed class

[pniederw]

@Nikky I don't understand your question

[pniederw]

@ephemient I want to directly serialize a Map<String, (Number|Boolean|String|List|Map)?> without any input conversion steps.

[ephemient]

not all formats will support variant types so if you want to be format agnostic you need a custom wrapper somewhere

[pniederw]

I think all I'm missing is Decoder.peekType(), a generalization of what JsonDecoder.decodeJsonElement already does.

[ephemient]

and not all formats will support that

[pniederw]

@ephemient I'm OK with doing this for all formats that support it.

[pniederw]

(in a format agnostic way)

[ephemient]

well that's basically just JSON

[pniederw]

you sure? I don't think that's correct

[pniederw]

and having this just for JSON would be much better than nothing

[ephemient]

properties format doesn't have types, relies on serialized type to know what the type of.
protobuf schema doesn't support variant types.
might work with cbor, not sure.

[ephemient]

to make it work work json just cast the decoder

[pniederw]

Yes, it does work for CBOR. JsonDecoder returns JsonElement, which requires me to recursively convert back to Map<String, (Number|Boolean|String|List|Map)?>, which is my current workaround.

[pniederw]

What would also help is an easy way to write a serializer that uses its own type tags.

[Nikky]

it sounds like what you want is to make the serializer of the value a argument to your Serializer so you can construct it the same way as MapSerializer(keySerializer, valueSerializer) or ListSerializer(valueSerializer)

[Nikky]

unless the type of your values in the map/object is mixed

[pniederw]

yes it's mixed, that's the point

[pniederw]

Basically I need to serialize Map<String, Any>. If necessary, I can tag values in the serialized format, but it's not clear to me how to make this work without using wrapper types similar to JsonElement on the Kotlin side (which I absolutely don't want), and it shouldn't be necessary as long as I'm using JSON/CBOR.

[ephemient]

just make a custom serializer that wraps/unwraps, see the doc I linked earlier

[pniederw]

I don't want to wrap on the Kotlin side because recursively wrapping/unwrapping a large data structure is inefficient. Even with internal wrapping, I'm not sure if I can have a KSerializer<Map<String, Any>> (last time I tried I got some compiler plugin error).