Mastering Kotlin

Implementation delegation

A class that implements an interface may implement all required methods by delegating to a specified delegate instance. In the following code, we've defined a SettingsProvider interface that is then implemented by a SettingsManager object:

interface SettingsProvider {    fun getSetting(key: String) : String}object SettingsManager : SettingsProvider {    private val map = HashMap<String, String>()    override fun getSetting(key: String)            = map.getOrDefault(key, "")}

Now, we want to define a UserManager class that will implement SettingsProvider by delegating to SettingsManager:

class UserManager : SettingsProvider by SettingsManager

We start by declaring the class name and adding the SettingsProvider interface, but then we ...