Android Singleton Kotlin

TasksLocalDataSource.kt

//http://stackoverflow.com/questions/40398072/singleton-with-parameter-in-kotlin

class TasksLocalDataSource private constructor(context: Context) : TasksDataSource {

    private val mDbHelper: TasksDbHelper

    init {
        // You cannot pass null in kotlin unless you are using `context: Context?`
        // therefore, checking null is useless 
        // checkNotNull(context)
        mDbHelper = TasksDbHelper(context)
    }

    companion object {
        // do not expose var, it includes getter/setting and makes confusion to other users
        @Volatile
        private lateinit var INSTANCE: TasksLocalDataSource
        private val initialized = AtomicBoolean(false)
        
        // Use `val` and define the getter only
        // kotlin will throw `kotlin.UninitializedPropertyAccessException` if the INSTANCE is not initialized
        val instance: TasksLocalDataSource get() = INSTANCE

        // Call it in Application.onCreate() is enough
        fun initialize(context: Context) {
            if(!initialized.getAndSet(true)) {
                INSTANCE = TasksLocalDataSource(context)
            }
        }
    }
}

shouldn't instance be private?

The instance in val instance: TasksLocalDataSource get() = INSTANCE is a getter function.