Example.kt

interface DataSource {
    fun getData(): String
}

class LocalDataClient: DataSource {
    override fun getData() = sharedPreferences.getString(KEY)
}

class RemoteDataClient: DataSource {
    override fun getData() = retrofit.getValue(KEY)
}

class DataViewModel(private val dataClient: DataSource) {
    fun getCachedData() = dataClient.getData()
}

// Container of objects shared across the whole project
class DependencyInjector {
    val localDataClient: DataSource = LocalDataClient()
    val remoteDataClient: DataSource = RemoteDataClient()
}