Hey would it be possible to create some sort of "optional" serializer? E.g. Some generic type that c...

# serialization

[fkrauthan]

Hey would it be possible to create some sort of "optional" serializer? E.g. Some generic type that can have 3 states (unset; set but null; set with value) and in case the generic type indicates its unset I don't want to include it in the serialization output?

[gildor]

Looks that you need some wrapper class for this to represent unset behaviour (like Optional<T?>) and write a custom serializer for it

[fkrauthan]

Yes exactly. But can a custom serializer for Optional<T?> decide to omit a field? or will it always write that field?

[gildor]

I believe yes, you call serialize/encode manually, so you can just do not write anyting, never tried though

[fkrauthan]

Hmm does not work unfortunately. I tried the following Code:

class ValueSerializer <T> (private val dataSerializer: KSerializer<T>) : KSerializer<Value<T>> {
    override val descriptor: SerialDescriptor = dataSerializer.descriptor

    override fun serialize(encoder: Encoder, value: Value<T>) {
        if (value.isSet) {
            if (value.value == null) {
                encoder.encodeNull()
            } else {
                dataSerializer.serialize(encoder, value.value!!)
            }
        }
    }
    override fun deserialize(decoder: Decoder) = TODO("Not implemented!")
}

But when running

val testObject = TestClass()
    testObject.value1.value = "Hello World"
    testObject.value3.value = null

    println(Json.encodeToString(testObject))

The output is {"value1":"Hello World","value2":,"value3":null}

[gildor]

hmm, yeah, it probably about JsonSerializer itself

[fkrauthan]

It's a very unique problem but would be cool if someone has an idea how I could do this

[gildor]

I think all logic about skipping values is baked to json serializer itself

[gildor]

so encoder will not help here

[gildor]

because it just encodes value, but it should be a part of serializer itself I believe

[gildor]

but unclear how to make it work per type

[fkrauthan]

yeah that would be the important component to have a generic system

[fkrauthan]

Like my main idea behind this is to have a simple "patch" system where I can ether not update a value or I can explicit set a value to Null

[fkrauthan]

and it would be cool if I can use this to create a JSON to be send to a server but also to receive on the server and put back into a object

[kqr]

I am wondering, that would mean that your request class would be full of this wrappers right?

[Vampire]

Maybe if you have a special "this is unset" marker value, then set this as default value and configure the JSON serializer to not encode default values.

[fkrauthan]

@kqr yes that is correct my request class would instead of String always have my OptionalValue<String> as data type for example. But its a small price to pay if I don’t have to work with basic JsonObject trees as I still get data safety etc. In that regards Javascript can be useful as you have undefined and null that you can use for that.