polymorphism-open.md

Open Polymorphism

Support for abstract classes is limited, as there is no concrete type. If a class must be polymorphic, instead prefer sealed polymorphism.

Abstract class with a single field

@Serializable
abstract class Color(val rgb: Int)

fun main() {
  val tsGenerator = KxsTsGenerator()
  println(tsGenerator.generate(Color.serializer()))
}

You can get the full code here.

export type Color = any;
// interface Color {
//   rgb: number;
// }

Abstract class with primitive fields

@Serializable
abstract class SimpleTypes(
  val aString: String,
  var anInt: Int,
  val aDouble: Double,
  val bool: Boolean,
  private val privateMember: String,
)

fun main() {
  val tsGenerator = KxsTsGenerator()
  println(tsGenerator.generate(SimpleTypes.serializer()))
}

You can get the full code here.

export type SimpleTypes = any;
// export interface SimpleTypes {
//   aString: string;
//   anInt: number;
//   aDouble: number;
//   bool: boolean;
//   privateMember: string;
// }

Abstract class, abstract value

@Serializable
abstract class AbstractSimpleTypes {
  abstract val aString: String
  abstract var anInt: Int
  abstract val aDouble: Double
  abstract val bool: Boolean
}

fun main() {
  val tsGenerator = KxsTsGenerator()
  println(tsGenerator.generate(AbstractSimpleTypes.serializer()))
}

You can get the full code here.

export type AbstractSimpleTypes = any;
// export interface AbstractSimpleTypes {
//   rgb: number;
// }

Open Polymorphism

Generics

Kotlinx Serialization doesn't have 'generic' SerialDescriptors, so KxsTsGen can't generate generic TypeScript classes.

import kotlinx.serialization.builtins.serializer

@Serializable
class Box<T : Number>(
  val value: T,
)

fun main() {
  val tsGenerator = KxsTsGenerator()

  println(
    tsGenerator.generate(
      Box.serializer(Double.serializer()),
    )
  )
}

You can get the full code here.

export interface Box {
  value: number;
}

JSON content polymorphism

Using a JsonContentPolymorphicSerializer means there's not enough data in the SerialDescriptor to generate a TypeScript interface. Instead, a named type alias to 'any' will be created instead.

import kotlinx.serialization.json.*

@Serializable
abstract class Project {
  abstract val name: String
}

@Serializable
data class BasicProject(override val name: String) : Project()

@Serializable
data class OwnedProject(override val name: String, val owner: String) : Project()

object ProjectSerializer : JsonContentPolymorphicSerializer<Project>(Project::class) {
  override fun selectDeserializer(element: JsonElement) = when {
    "owner" in element.jsonObject -> OwnedProject.serializer()
    else                          -> BasicProject.serializer()
  }
}

fun main() {
  val tsGenerator = KxsTsGenerator()
  println(tsGenerator.generate(ProjectSerializer))
}

You can get the full code here.

export type Project = any;