CODEWITHSUNDEEP
genericstypesnestedkotlin
Raphael
Raphael

Reputation: 10559

Accessing type parameters of outer type

In Kotlin, we can define nested interfaces. If the outer interface is generic (here just to simulate a proper Self meta-type, but one can imagine other uses), can I refer to its type parameter from the inner type?

That is, I want to achieve (an equivalent of) this:

interface JsonRepresentable<Self: JsonRepresentable<Self>> {
    fun toJson(): String

    interface Companion {
        operator fun invoke(json:String): Self?
    }
}

Upvotes: 0

Views: 318

Answers (1)

glee8e
glee8e

Reputation: 6419

No, you can't. An interface can't be a non-static inner class, which is a platform constrain that can't be overcame by Kotlin. I know it would be pretty useful to constrain how the companion object should be, but this haven't been considered yet. I don't know if JetBrains will ever take this suggestion seriously.

In your attempt, those two interfaces are NOT related at all, except that you can find KClass<Compaion> in JsonRepresentable::class.nestedClasses. The relationship between these interfaces can be compared to the relationship between a Java static inner class and its declaring class.

Upvotes: 2

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