How to create compile-time constant in Kotlin from enum? - kotlin

Question

I have an annotation that requires defaultValue to be compile-time constant. I take defaultValue from enum below:
enum class RaceType {
MARATHON,
SPRINT;
companion object {
fun apply(type: RaceType): RaceDto {
return when (type) {
MARATHON -> MarathonDto()
SPRINT -> SprintDto()
}
}
}
}
My dtos are the following:
interface RaceDto {
}
data class MarathonDto: RaceDto
data class SprintDto: RaceDto
when I use annotation #QraphQLArgument(defaultValue = RaceType.SPRINT.name) Kotlin requires RaceType.SPRINT.name to be compile-time constant.
Annotation implementation itself:
#Retention(RetentionPolicy.RUNTIME)
#Target({ElementType.PARAMETER})
public #interface GraphQLArgument {
String NONE = "\n\t\t\n\t\t\n\ue000\ue001\ue002\n\t\t\t\t\n";
String NULL = "\n\t\t\n\t\t\n\ue000\ue001\ue002\ue003\n\t\t\t\t\n";
String name();
String description() default "";
String defaultValue() default "\n\t\t\n\t\t\n\ue000\ue001\ue002\n\t\t\t\t\n";
Class<? extends DefaultValueProvider> defaultValueProvider() default JsonDefaultValueProvider.class;
}
I looked through similar questions but don't see a way how it can be resolved. I also found article related to the topic but nothing worked so far.
Side note: I cannot change annotation since it is from the library and I cannot change the library as well.
To summarize, is there a way to make from enum compile-time constant in Kotlin to use in an annotation?

Answer 1

is there a way to make from enum compile-time constant in Kotlin to use in an annotation?
No, because formally enums aren't compile-time constants in Java.
However please consider the sealed classes:
sealed class RaceType {
object MARATHON: RaceType() {
const val name = "MARATHON" // copy-paste is required here until https://youtrack.jetbrains.com/issue/KT-16304
}
object SPRINT: RaceType()
companion object {
fun apply(type: RaceType): RaceDto {
return when (type) { // the check is in compile time, because of sealed class
MARATHON -> MarathonDto()
SPRINT -> SprintDto()
}
}
}
}
A little part of copy-paste is still required. Please vote on kotlin compiler bug or follow this thread.
However, as I understand, this doesn't solve your issue with #QraphQLArgument(defaultValue = RaceType.SPRINT.name) unfortunately, because the name of class is not the same with value. In the other words, with sealed classes you need to write code to convert input strings to them.