Say I have `annotation class RunCount(val count: ...

# multiplatform

[Justin]

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?

[Dominaezzz]

Make RunCount an interface?

[Justin]

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

[Dominaezzz]

You can use delegation.

[Justin]

Can you elaborate?

[Dominaezzz]

Something like

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

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

[Justin]

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

[Justin]

I know I can get an array of annotations using reflection on the type

[Justin]

Is it not possible to get the same thing on an instance of a type?

[Dominaezzz]

With Java you could use reflection but in multiplatform you can do some hacks with kotlinx.serialization but I wouldn't recommend it.

[Justin]

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

[Dominaezzz]

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

[Dominaezzz]

Although there's an annotation processor that might just suit your needs. One sec.

[Dominaezzz]

https://kotlinlang.slack.com/archives/C7L3JB43G/p1567356910004600

[Justin]

Thanks @Dominaezzz, I’ll check that out