Hello, I'm modeling the different types of audio focus as a Kotlin type hierarchy, and I'm unsure ab...

# codereview

[louiscad]

Hello, I'm modeling the different types of audio focus as a Kotlin type hierarchy, and I'm unsure about picking sealed interface or sealed class.

What would you pick? Any reason beyond personal preference?

1️⃣ Here's with `interface`:

sealed interface AudioFocus {
    object Gain : AudioFocus
    sealed interface Loss : AudioFocus {
        companion object : Loss
        sealed interface Transient : Loss {
            companion object : Transient
            object CanDuck : Transient
        }
    }
}

2️⃣ Here's with `class`:

sealed class AudioFocus {
    object Gain : AudioFocus()
    sealed class Loss : AudioFocus() {
        companion object : Loss()
        sealed class Transient : Loss() {
            companion object : Transient()
            object CanDuck : Transient()
        }
    }
}

[Javier]

If an interface can be used, I would use it, if you need local variables with backing fields, I would use a class

[ephemient]

sealed interfaces don't protect you from instantiation in Java, so at least until support for JEP 360 lands, I'd use sealed classes except when interfaces are required (multiple hierarchies, enums)

[ephemient]

on a different note, while the use of companion object here will look nice with AudioFocus.Loss being usable as a value, I think it's awkward that its type is actually AudioFocus.Loss.Companion.

[ephemient]

I don't really have a better option though

[ephemient]

although because AUDIOFOCUS_GAIN_TRANSIENT AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK AUDIOFOCUS_GAIN_TRANSIENT_EXCLUSIVE also exist, I think this hierarchy isn't really so clean…

[Zach Klippenstein (he/him) [MOD]]

1 if you’re only targeting kotlin consumers, 2 if you are worried about java consumers

[ephemient]

something like this, with a DAG-like set of hierarchies instead of a single tree-like hierarchy, is only doable with interface

Untitled.kt

[louiscad]

Thanks for sharing your thoughts! I settled with sealed interface (Java compatibility isn't a concern in my case).

Here's a full gist that includes a suspend-first API to work with AudioFocus on all Android versions:
https://gist.github.com/LouisCAD/4ca4bd6cb85e3d8b2509492d67b282f7