What is the suggested approach for declaring a typ...

# serialization

[Justin]

What is the suggested approach for declaring a type that is basically Any but constrained to String | Boolean | Int | Array | Map, and then make that type serializable?


Because there are no true union types in Kotlin, what I tried to do is this:

@Serializable
sealed class Value<out T>(val value: T) {
    class STRING(value: String): Value<String>(value)
    class BOOLEAN(value: Boolean): Value<Boolean>(value)
    class NUMBER(value: Number): Value<Number>(value)
    class ARRAY<V>(value: List<V>): Value<List<V>>(value)
    class DICTIONARY(value: Map<String, Any?>): Value<Map<String, Any?>>(value)
    object NULL: Value<Nothing?>(null)
}

Then, I have a number of data classes/interfaces that need to use this type, for example:

interface StoredValue {
    val type: String
    val value: JsonElement // This would become of type Value
}

@Serializable
data class NetworkRequest(
    val type: String,
    val data: JsonElement // This would become of type Value
)

But if I try to use Value in place of JsonElement, then I need to attach the generic type parameter to those classes/interfaces, and then I'm not sure how to deal with serialization on them.

[Big Chungus]

create marker interface and wrapper objects for those types that has value as prop and extend marker interface

[Big Chungus]

That's what dukat is doing

[Big Chungus]

e.g.

interface StringOrNumber
inline class MyString(val value:String):StringOrNumber
inline class MyNumber(val value:Number):StringOrNumber

Inline classes are great for that as well as compiler unboxes them when spitting out bytecode