Example showing how to decouple interface from implementation in an example from Robert Martin using generics.

Api.kt

package com.myorg.myapp.api

data class AlbumData(
    val title: String,
    val released: DateTime,
    val artist: String
)

interface AlbumService {
    suspend fun getAlbums(): List<AlbumData>
}

interface Application<E>: MakeAlbumService<E> {
    fun runApplication()
}

interface MakeAlbumService<E> {
    fun makeService(label: E): AlbumService
}

Implementation.kt

package com.myorg.myapp.implementation

import com.myorg.myapp.api.*

enum class ServiceType {
    Local, Remote;
}

object AlbumApplication: Application<ServiceType> {
    override fun makeService(label: ServiceType): AlbumService =
        when (label) {
            ServiceType.Local  -> LocalAlbumService()
            ServiceType.Remote -> RemoteAlbumService()
        }

    override fun runApplication() {
        ...
    }
}

class LocalAlbumService: AlbumService {
    ... 
}

class RemoteAlbumService: AlbumService {
    ... 
}