I'm getting a `kotlinx.serialization.SerializationException` but the error doesn't make sense. This ...

# getting-started

[Chris B]

I'm getting a kotlinx.serialization.SerializationException but the error doesn't make sense. This is the error:

Exception in thread "main" kotlinx.serialization.SerializationException: Serializer for subclass 'GridClueSelection' is not found in the polymorphic scope of 'Selection'.
Check if class with serial name 'GridClueSelection' exists and serializer is registered in a corresponding SerializersModule.
To be registered automatically, class 'GridClueSelection' has to be '@Serializable', and the base class 'Selection' has to be sealed and '@Serializable'.

except GridClueSelection is Serializable, and Selection is sealed and Serializable.

[Chris B]

@Serializable
sealed class Selection { ... }

@Serializable
abstract class ClueSelection(val clueKey : String) : Selection() { ... }

@Serializable
class GridClueSelection( ... ) : ClueSelection(_clueKey) { ... }

[Michael Krussel]

I'm guessing that since ClueSelection is not sealed, the automatic lookup polymorphism for GridClueSelection is not getting created, and you will need to manually configure the serializers.

[Chris B]

So the error message is wrong?

[Chris B]

That did fix the problem.

[Michael Krussel]

No it is right. GridClueSelection is not in the polymorphic scope of Selection because it is not a subclass of Selection and is instead a subclass of ClueSelection. I don't know if making ClueSelection sealed will fix it or if you need to manually configure if the polymorphic scope of Selection.

[Chris B]

The error specifically says "To be registered automatically, class 'GridClueSelection' has to be '@Serializable', and the base class 'Selection' has to be sealed and '@Serializable'"

[Chris B]

At best that's misleading. It's necessary but not sufficient.

[Michael Krussel]

Yeah, the message message about what to check is wrong, but not what is wrong. They need to add an extra check to make, I guess.

[Chris B]

I guess they weren't thinking of an inheritance hierarchy when they wrote it.

[Joffrey]

I guess the message should say that all super classes need to be sealed too

[Michael Krussel]

Not all super classes, just the ones in between the serialized polymorphic root and the leaf. Object obviously won't be sealed or Serializable.