CODEWITHSUNDEEP
genericsannotationskotlin
glee8e
glee8e

Reputation: 6419

What is the kotlin equivlant to Java annotation field with bounded wildcard type?

Say I have an annotation in Java like this:

public @interface Foo {
    Class<? extends Bar> value();
}

public interface Bar {}

How should I translate Foo into kotlin? Is it true that I could only switch back to Java in such situation?

Upvotes: 1

Views: 1079

Answers (1)

marstran
marstran

Reputation: 28056

Kotlin annotations cannot have method-definitions. They can, however, have constructor parameters. I think this works like you want it to:

import kotlin.reflect.KClass

interface Bar
class Foo : Bar

@Target(AnnotationTarget.FUNCTION)
annotation class Test(val value: KClass<out Bar>)

@Test(Foo::class)
fun testAnnotation() {
    println("Test")
}

Notice the out modifier on the KClass type parameter. It makes the type parameter covariant, meaning it can be of type Bar or any type that implements Bar.

Upvotes: 3

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