Say I have

annotation class RunCount(val count: Int)

open class Testable

...and...

@RunCount(3)
class TestA: Testable { ... }

With an instance, like:

val testA = TestA()

how can I figure out which annotations it has? For example, I tried this:

if (testA is RunCount) ...

But that doesn’t work. Any ideas?

Make

RunCount

an interface?

I could do that, but I was hoping to use annotations because I have about 20 of them (some of which take values), and they are more ergonomic to apply to test data classes than adding conformance to a bunch of interfaces

You can use delegation.

Can you elaborate?

Something like

interface RunCount {
    val count: Int
}
class RunCountImpl(override val count: Int)

class TestA : Testable, RunCount by RunCountImpl(3) {
}

I see. I’d still rather use annotations if it’s possible to check which annotations are applied to an instance of a class.

With Java you could use reflection but in multiplatform you can do some hacks with

kotlinx.serialization

but I wouldn't recommend it.

How are annotations intended to be used in Kotlin if not like this then?

Kotlin Multiplatform isn't quite there yet, waiting for Kotlin 1.4 to bring nicer support for things like this.

Thanks @Dominaezzz, I’ll check that out