The problem is that for your decodeFunctionReturnValue function the type parameter T is not reified. Therefore at runtime the TypeToken you are creating is actually TypeToken<JsonFunctionReturnValueData<Object>>. When deserializing Object, Gson creates based on the JSON data standard objects, for a JSON object that is a Java Map (and Gson’s internal implementation is LinkedTreeMap).

So if possible the solution would be to make the type parameter T here reified as well. If that is not possible, maybe the type can be passed as separate TypeToken parameter to the function.

As side note: It was already suggested that Gson should throw an exception when a TypeToken capturing a type variable is created (which would have informed you about the problem with your code). However, due to backward compatibility concerns this was not implemented yet.

I have a problem that appear be simple, but im making something wrong.

How i can convert from a generic class with reified using GSON and Kotlin in my project called XPLPC?

The error is here:
https://github.com/xplpc/xplpc/actions/runs/3395808126/jobs/5646151499#step:9:503

com.xplpc.library.TodoTest > singleItem[test(AVD) - 12] FAILED 
    java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to com.xplpc.library.TodoTest$Todo
    at com.xplpc.library.TodoTest.singleItem(TodoTest.kt:44)

It don’t understand that i want convert to Todo class instead of LinkedTreeMap.

The code is here:
https://github.com/xplpc/xplpc/blob/main/kotlin/lib/library/src/main/java/com/xplpc/serializer/JsonSerializer.kt#L66-L79

And the code is called by this function:
https://github.com/xplpc/xplpc/blob/main/kotlin/lib/library/src/main/java/com/xplpc/client/RemoteClient.kt#L14-L27

Basically the code is:

// Part 1
object RemoteClient {
    inline fun <reified T> call(request: Request, defValue: T? = null): T? {
        try {
            val data = PlatformProxy.call(request.data)
            println(data)
            return XPLPC.config.serializer.decodeFunctionReturnValue<T>(data)
        } catch (e: Exception) {
            Log.e(
                Constants.LOG_GROUP,
                "[RemoteClient : call] Error when try to decode return value: ${e.message}"
            )
        }

        return defValue
    }

    inline fun <reified T> callAsync(request: Request, defValue: T? = null): Deferred<T?> {
        return CoroutineScope(Dispatchers.IO).async {
            [email protected] call<T>(request, defValue)
        }
    }
}

// Part 2
override fun <T> decodeFunctionReturnValue(data: String): T? {
    try {
        val type = object : TypeToken<JsonFunctionReturnValueData<T>>() {}.type
        val gson = createGson()
        return gson.fromJson<JsonFunctionReturnValueData<T>>(data, type).r
    } catch (e: Exception) {
        Log.e(
            Constants.LOG_GROUP,
            "[JsonSerializer : decodeFunctionReturnValue] Error when parse json: ${e.message}"
        )
    }

    return null
}