kotshi/se.ansman.kotshi/Polymorphic

Polymorphic

@Target(allowedTargets = [AnnotationTarget.CLASS])

annotation class Polymorphic(val labelKey: String, val onMissing: Polymorphic.Fallback = Fallback.DEFAULT, val onInvalid: Polymorphic.Fallback = Fallback.DEFAULT)(source)

Annotation to be placed on a sealed class to describe how it should be parsed.

The label key should point out the key in the json to use when figuring out which subtype the json represents. The value can be either a string or a number, in which case it's parsed as a string.

Subclasses use the PolymorphicLabel annotation to indicate which value represents that subtype.

If you want to use a fallback in case the type is invalid or missing you can annotate one of the subtypes with JsonDefaultValue.

Example:

@JsonSerializable
@Polymorphic(labelKey = "handType")
sealed class HandOfCards

@JsonSerializable
@PolymorphicLabel("blackjack")
data class BlackjackHand(val hiddenCard: Card, val visibleCards: List<Card>) : HandOfCards()

@JsonSerializable
@PolymorphicLabel("holdem")
data class HoldemHand(val hiddenCards: List<Card>) : HandOfCards()