Hey everyone wave I am trying to create a gson type adapter

Question

Hey everyone wave I am trying to create a gson type adapter to process the object after it is de serialized following the pattern described here However not getting the right approach to convert that impl to Kotlin Specifically using generic type on an interface and apply the interface to an annotation class Could someone provide any ideas or hint to get this approach right This is what I have got so far

Skc · Answer

Problem that I am running into is that I cant use a type for my interface which is passed as an argument to the annotation class so I tried to use ` ` projection ``` Retention AnnotationRetention RUNTIME Target AnnotationTarget CLASS annotation class EmptyObjectValidator val deserializer KClass lt out JsonPostDeserializer lt gt gt ``` ^ this enables me to use the concrete impl for any class with annotation e g ``` EmptyObjectValidator FluffValidator class data class Fluff val blah String = ``` and this is how the concrete impl might look like ```class FluffValidator JsonPostDeserializer lt Fluff gt override fun postDeserialize type Fluff TODO Not yet implemented ```

Skc · Answer

However use of ` ` projection type doesn t allow me to call the interface method when called like this ```val objectValidator = type rawType getAnnotation EmptyObjectValidator class java return null override fun read `in` JsonReader T val result = delegate read `in` val postDeserializer JsonPostDeserializer lt gt = objectValidator deserializer javaObjectType newInstance postDeserializer postDeserialize result return result ``` it errors out when calling the method here `postDeserializer postDeserialize result `

ephemient · Answer

on one hand you can ```annotation class EmptyObjectValidator lt T gt val deserializer KClass lt out JsonPostDeserializer lt T gt gt EmptyObjectValidator lt Fluff gt FluffValidator class ``` instead of using a raw type in the annotation but regardless I think your caller will need to perform an unchecked cast since ` getAnnotation` won t understand the generic there