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hey serialization friends- I've looked at <https://github.com/Kotlin/kotlinx.serialization/blob/mast...
# serialization
c
hey serialization friends- I've looked at https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/json.md#content-based-polymorphic-deserialization but I wonder if it's possible to augment how a single field is deserialised based on another field. Something like:
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{
  "type": "STATE",
  "state": {
    "foo": "bar"
  }
}
and
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{
  "type": "STATE-CHANGE",
  "state": {
    "foo": [
      "bar",
      "baz"
    ]
  }
}
I'm not clever enough to parse the documentation to understand if that is possible, or if I need to go turbo and make a custom serializer
a
a regular ol’ sealed class should handle that situation, if you use a separate subclass for each response type https://github.com/Kotlin/kotlinx.serialization/blob/v1.5.1/docs/polymorphism.md#sealed-classes
c
I went with a sealed interface and that didn't seem to work, I'll try a sealed class instead, cheers Adam
a
what problem did you have? There shouldn’t be a significant difference between a sealed class and sealed interface. Did you set 
@SerialName("STATE-CHANGE")
and 
@SerialName("STATE")
on the subclasses?
c
oh 😮 wait, I can set a discriminator based on the type field?
ok I really need to read the docs now
because that's starting to make sense!
because the type implies the state field's type, I was confused how I could associate them
a
yeah, it should just work! Normally it’s a little bit awkward to decode polymorphic JSON because not all JSON has the 
type
field, but it looks like you’re lucky
c
thank dyson for that >_>, <_<
a
the vacuum company?
c
the very same
a
haha weird
c
wait so, their actual data structure uses a 'message' field, not a 'type' one
if I literally change the json text to replace "message" with "type" 😂 would that actually work? Sorry I'm doing that thing where I ask questions instead of just trying
a
yeah, that should work
and no problem, questions are good :)
try taking a look at this answer, it tackles a similar problem https://stackoverflow.com/a/73145311/4161471
c
ok I was looking at this all wrong thinking about it, I messed up my representation of the data structures coming back, I think I can do everything I need now. What I was trying to do was have a kind of generic parent class called 
Message
and the contents of that class would vary wildly depending on the type of message being received. I was trying to be able to deserialise the 
Message
type with a single member having it's class type changed, but that's a no go. What's more accurate and easier to deal with, is having a sealed interface called 
Message
and a 
StateMessage
and 
StateChangeMessage
accordingly
cheers @Adam S, really helped us crack the case on this one
a
yeah exactly! It’s really best to be as explicit as possible with KxS, and avoid generic types. So even if you did need some generic typed class, e.g.
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class Message<T>(
  val contents: T
)
instead make T sealed, and remove the generic type from Message
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class Message(
  val contents: MessageContent
)
That’s a rough rule of thumb, it won’t always hold. And it seems a bit weird and counter-intuitive, but it will pay off with explicitness.
c
the compile time nature of the serializers makes that a requirement too right?
a
basically, yeah. KxS can handle classes with generic types, but it just requires a bit more setup and care, so you have to manually specify them.
so it’s not a strict requirement, but it does require some manual definition
c
cheers dude, really appreciate the heads up! I can confirm I can get all kinds of status updates from my fan now 😂
a
haha, good to know
what fan do you have?
c
the Dyson Pure Cool, you can get them for like 100 quid off refurb on ebay
though when I got mine, they sent me the wrong remote... which I think was a guerilla attempt to get me to download the app
it has an MQTT interface that I got integrated into home assistant thanks to the work of some legend on github (https://github.com/shenxn/libdyson) and now I'm just working it into my little remote control noddy app I've got for learning KMM
a
ahh that’s cool, thanks for the tip
c
fwiw too! If I change the classDisriminator property on the 
Json
instance used to deserialise the object I don't have to text replace 
msg
to 
type
which is cool
a
oooh yes, good point, I forgot about that
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