Might be a strange question but how do you write a...

# serialization

[ghedeon]

Might be a strange question but how do you write a serializer for kotlin.Result class?
Let say I want to write a custom call adapter for Retrofit that wraps all my requests in Result class. Right now serialization converter is failing with Can't locate argument-less serializer for class kotlin.Result which sounds reasonable. How would one workaround this situation?

[spand]

Seems like asking for trouble serializing its Throwable no ?

[ghedeon]

I don't expect serialization to happen at all, I can even leave it not implemented. The only reason it's an issue is that my requests return Result<T> now, where T is an actual object to deserialize from json and Result is something that kotlin serialization is not aware of. As you can imagine, it's one way.

[Nikky]

so you want a Result.Success<T> to serialize like a T ?

[ghedeon]

you can say that, yes. Although, this path should never be called, I can even throw NotImplemented exception or something.

[Nikky]

val <T> T.result: KSerializer<Result<T>> = ResultSerializer<T>(this)

for the shorthand

[Nikky]

that way the ResultSerializer has the child serializer and can call it

[ghedeon]

Not sure where I'm supposed to put it. As you can imagine, I don't controll deserialization manually, it happes inside of Retrofit. So, by the time the call is performed, the Result Serializer is expected to be registered somewhere...

[Nikky]

you pass retrofit some sort of Json object right ?

[Nikky]

anyways this is the Serializer i would use.. not sure if it will work..

class ResultSerializer<T: Any>(val childSerializer: KSerializer<Result<T>>) : KSerializer<Result<T>> {
    override val descriptor: SerialDescriptor = SerialClassDescImpl(Result::class.simpleName!!)
    override fun deserialize(decoder: Decoder): Result<T> {
        TODO()
    }
    override fun serialize(encoder: Encoder, obj: Result<T>) {
        encoder.encodeSerializableValue(childSerializer,obj)
    }
}

[ghedeon]

well, somewhere internally that's what is happening, yes. But I don't pass anything, it's already abstracted for the user. All you have to do is fun foo(): Bar where Bar must be serializable. And now it's fun foo(): Result<Bar>.

[Nikky]

you register it to use kotlinx-serialization somehow though ?

[Nikky]

otherwise does theu ser have no control over the Json options ?

[ghedeon]

yep

.addConverterFactory(Json.asConverterFactory(MediaType.get("application/json")))

[Nikky]

is it this ? https://github.com/JakeWharton/retrofit2-kotlinx-serialization-converter

[Nikky]

i think you can use Json() too there

[Nikky]

and install default modules or whatever they are called in there

[Nikky]

otherwise ping the author i guess

[Nikky]

https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/custom_serializers.md#registering-and-context
keyword: SerialModule

[Nikky]

that is what kotlinx-serialization should use to look up the serializer for Result .. not sure how to register it in a way that the retrofit adapter supports