I’m using polymorphic serialization in an app, and...

# serialization

[Landry Norris]

I’m using polymorphic serialization in an app, and I get a serialization error when I run in release mode, but not debug mode.

[Landry Norris]

The error I get is “l.d.j: Serializer for class ‘c’ is not found.
E/AndroidRuntime(27144): Mark the class as @Serializable or provide the serializer explicitly.”

I have tried applying the serialization plugin to the final app as well as providing the serializer explicitly, and get the same error.

[Landry Norris]

The class and function that calls Json.encodeToString(strategy, value) are in another library that gets imported as an aar.

[ephemient]

that sounds like there's something that is trying to look up a serializer at runtime (which is also what happens with encodeToString<T>(value)), getting the stacktrace and looking up the original (pre-proguard) classes with retrace should help you narrow down where that is happening

[ephemient]

but also the README contains some proguard rules that make it possible for runtime serializer lookup to work, https://github.com/Kotlin/kotlinx.serialization#android

[Landry Norris]

I refactored my code to remove encodeToString<T> and use the version passing in a serializer explicitly instead. I was under the impression that this method would not have to look up the type at runtime. Does this apply to polymorphic classes as well?

[ephemient]

good. until https://github.com/Kotlin/kotlinx.serialization/issues/1348 is resolved, that is the best approach

[ephemient]

the reified helper uses reflection currently, due to lack of compiler assistance

[Landry Norris]

I seem to get the same error with the encodeToString that passes the serializer explicitly. I wonder if polymorphism causes it to use reflection?

[ephemient]

serializable sealed classes are registered at compile time

[ephemient]

but if you're registering other polymorphic classes via serializersModule, there are reified helpers there that also currently rely on reflection

[Landry Norris]

I did make sure that my classes are sealed.

[Landry Norris]

It turned out I forgot to update decodeFromString to use the non-reflective version as well. Fixed that and the code doesn’t crash anymore.