CODEWITHSUNDEEP
androidkotlinserialization
Brett
Brett

Reputation: 1837

Generics in Kotlin Serialization produces compile time error

I am having trouble compiling a Serialization data class that is also a generic. I am very new to Android and Kotlin, but am an experienced iOS/Swift developer (don't hold it against me).

I am trying to set up a generic data class wrapper around a GraphQL Response that can return me either the T generic in a data field, or an error in the error field.

import kotlinx.serialization.Serializable

@Serializable
data class GraphQLResponse<T:Serializable> (
    val errors : List<ErrorResponse>? = null,
    val data : Map<String, T>? = null
) {
    @Serializable
    data class Location(
        val line: Int? = 0,
        val column: Int? = 0,
        val sourceName: String? = null
    )

    @Serializable
    data class ErrorResponse(
        val locations: List<Location>? = null,
        val errorType: String? = null,
        val message: String? = null
    )
}

Compiling this I get the following error:

java.lang.AssertionError: Couldn't load KotlinClass from /Users/brett/Development/Company/android/app/build/tmp/kotlin-classes/debug/com/company/company/network/GraphQLResponse.class; it may happen because class doesn't have valid Kotlin annotations

And also a bunch of warning around reflection.

Is what I am trying to do possible with Generics and Serialization? Do I need to write my own deserialisation methods ?

Any help and advice would be appreciated.

Upvotes: 6

Views: 2042

Answers (1)

SorrowBeaver
SorrowBeaver

Reputation: 88

You need to provide a custom serializer for type T. check this guide (BTW, in your code type T shouldn't be Serializable - T:Serializable. It's just annotation)

There is a similar question, check this out. However, as you can see it may not work well if you use kapt in your project even you provide the serializer.

I found this comment from the serialization repository :

However, due to the mentioned kapt issue, it's impossible for now. Probably, a viable workaround can be to move models and serializers to the separate Gradle module, which is not processed by kapt.

And there are more issues about this problem :

Upvotes: 1

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