pahill

abstract class NetworkBoundResource<ResultType, RequestType> (private val appExecutors: AppExecutors) {
    //LiveData that represents the resource, implemented in the base class
    val result: MutableLiveData<Resource<ResultType>> = MutableLiveData()

    //Called to get the cached data from the database
    @WorkerThread
    abstract fun loadFromDb(): ResultType?

    //Called with the data in the database to determine when it was fetched
    //from the network

pahill

/**
 * A generic class that describes data with a status
 */
class Resource<T> constructor(val status: Status, var data: T? = null, val message: String? = null, val date: Date? = null) {

    companion object {
        fun <T> success(data: T?, date: Date?): Resource<T> {
            return Resource(status = Status.SUCCESS, data = data, date = date)
        }

pahill

class UserRepository (private val webservice: UserApi, private val userDao: UserDao, private val appExecutors: AppExecutors){

    fun loadUser(userId: Int) : LiveData<Resource<User>>{
        return object : NetworkBoundResource<User, User> (appExecutors) {
            override fun loadFromDb(): User? {
                return userDao.load(userId)
            }

            override fun getDataFetchDate(data: User?): Date? {
                return data?.fetchDate

pahill

class MoveAction {
    operator fun invoke(units: Int, direction: String) {...}
    operator fun invoke(targetPoint: Point) {...}
}

val move = MoveAction()
val targetPoint = Point(90, 90)

move(5, "left")
move(targetPoint)

pahill

class SpaceShuttle {
    operator fun invoke(units: Int, direction: String) {...}
    operator fun invoke(targetPoint: Point) {...}
}

val spaceShuttle = SpaceShuttle()
val targetPoint = Point(90, 90)

spaceShuttle(5, "left")
spaceShuttle(targetPoint)

pahill

class Memento(private val originalText: String) {    
}

interface UndoCommand {
    operator fun invoke()
}

class UndoTypingCommand(private val memento: Memento) : UndoCommand {
    override operator fun invoke() { 
        //restore the state using the memento object

pahill

val translucentRed = Color.valueOf(1.0f, 0.0f, 0.0f, 0.5f)

//Destructuring declarations operator extension functions - Color already exists in the android.graphics package
operator fun Color.component1() = this.red()
operator fun Color.component2() = this.green()
operator fun Color.component3() = this.blue()
operator fun Color.component4() = this.alpha()

//Assign variables using destructuring declaration
val (red, green, blue, alpha) = translucentRed

pahill

fun return1And2(): Pair<String, String> {
    return "returnValue1" to "returnValue2"
}

val (r1, r2) = return1And2()

pahill

data class Point(private val x: Double, 
                 private val y: Double) {
    operator fun minus(other: Point): Double {
        //Pythagorian algorithm - not important here!
        return sqrt(pow(x - other.x, 2.0) + pow(y - other.y, 2.0))
    }
}

val spaceStationPosition = Point(100.0, 100.0)
val spaceShuttlePosition = Point(10.0, 10.0)

pahill

data class Point(private val x: Double,
                 private val y: Double) {
    operator fun minus(other: Point): Double {...}
    operator fun compareTo(other: Point): Int {
        val distanceToOrigin = this - Point(0.0, 0.0)
        val otherDistanceToOrigin = other - Point(0.0, 0.0)
        return when {
            distanceToOrigin > otherDistanceToOrigin -> 1
            distanceToOrigin == otherDistanceToOrigin -> 0
            else -> -1