How can I serialize deserialize a `Map lt String Map lt Stri

Question

How can I serialize deserialize a `Map lt String Map lt String Any gt gt ` where `Any` can be one of `String` `Set lt String gt ` or `Map lt String String gt ` I don t mind if instead of `Any` I d have a `sealed interface AnyValue` with wrappers for those options although I d maybe prefer a `value class` that could have my own helper functions to cast and retreive one of those I would know in advance which one it is using the `String` key in the inner map

Adam S · Answer

it might be easier to decode to a JsonObject and then manually decode

Adam S · Answer

I answered a similar question here <https kotlinlang slack com archives C0B8MA7FA p1672313784581899 thread ts=1672310136 005409 amp cid=C0B8MA7FA>

dave08 · Answer

Thanks I guess I could get the Ktor client to return a String and then just use decodeToJsonElement

Adam S · Answer

if you wanted to set up `sealed interface AnyValue` then you could use value classes for the `String` `Set lt String gt ` `Map lt String String gt ` then you would have your own type hierarchy If the value classes were ` Serializable` then the plugin generated serializers would work just fine The slightly tricky bit would be writing the KSerializer for `AnyValue` It wouldn t be too hard if you used the `JsonPolymorphicSerializer` or whatever the real name is provided by KxS

dave08 · Answer

Yeah the only thing is that I don t think you can use value classes in sealed interfaces yet and they would probably be boxed anyways as soon as you use the interface in the map value

Adam S · Answer

I m sure you can

Adam S · Answer

Something like this should work except there s a bug ```Exception in thread main java lang IndexOutOfBoundsException Index 1 out of bounds for length 0 at java base jdk internal util Preconditions outOfBounds Preconditions java 64 at java base jdk internal util Preconditions outOfBoundsCheckIndex Preconditions java 70 at java base jdk internal util Preconditions checkIndex Preconditions java 248 ``` I ve made an issue <https github com Kotlin kotlinx serialization issues 2159>

dave08 · Answer

See <https github com Kotlin KEEP blob 3adcaf7c6e5d2ff756d26d2b60ba494947a72678 proposals sealed inline classes md>

dave08 · Answer

and <https youtrack jetbrains com issue KT 27576 Support inline sealed classes> which is scheduled for Kotlin 1 9

Adam S · Answer

ahh right yes Inline classes can t extend abstract open sealed classes Inline classes can extend from interfaces though

dave08 · Answer

I think the problem is that as soon as you use an interface it boxes the value class and there is no real benefit I guess the proposed KEEP is to have a special sealed value interface that doesn t box

dave08 · Answer

Actually it s a sealed value class in the KEEP

Adam S · Answer

I m confused by KT 27576 I thought that sealed classes were already implemented in 1 4 My guess is that it s specifically regarding JVM Currently Kotlin has a bespoke implementation that requires some under the hood workarounds so if JVM supports value classes natively then Kotlin will migrate to that

Adam S · Answer

anyway I m promoting the use of value classes here not because they re more performant but because it means KxS can automatically generate a serializer that matches the internal type which is very convenient