This commit is contained in:
mikr
@@ -0,0 +1,6 @@
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inline fun <reified T> Iterable<*>.filterIsInstance() = filter { it is T }
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fun main(args: Array<String>) {
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val set = setOf("1984", 2, 3, "Brave new world", 11)
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println(set.filterIsInstance<Int>())
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}
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@@ -0,0 +1,35 @@
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package com.baeldung.kotlin.delegates
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val data = arrayOf<MutableMap<String, Any?>>(
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mutableMapOf(
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"id" to 1,
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"name" to "George",
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"age" to 4
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),
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mutableMapOf(
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"id" to 2,
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"name" to "Charlotte",
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"age" to 2
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)
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)
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class NoRecordFoundException(id: Int) : Exception("No record found for id $id") {
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init {
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println("No record found for ID $id")
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}
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}
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fun queryForValue(field: String, id: Int): Any {
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println("Loading record $id from the fake database")
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val value = data.firstOrNull { it["id"] == id }
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?.get(field) ?: throw NoRecordFoundException(id)
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println("Loaded value $value for field $field of record $id")
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return value
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}
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fun update(field: String, id: Int, value: Any?) {
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println("Updating field $field of record $id to value $value in the fake database")
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data.firstOrNull { it["id"] == id }
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?.put(field, value)
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?: throw NoRecordFoundException(id)
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}
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@@ -0,0 +1,13 @@
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package com.baeldung.kotlin.delegates
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import kotlin.properties.ReadWriteProperty
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import kotlin.reflect.KProperty
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class DatabaseDelegate<in R, T>(private val field: String, private val id: Int) : ReadWriteProperty<R, T> {
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override fun getValue(thisRef: R, property: KProperty<*>): T =
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queryForValue(field, id) as T
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override fun setValue(thisRef: R, property: KProperty<*>, value: T) {
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update(field, id, value)
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}
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}
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@@ -0,0 +1,64 @@
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package com.baeldung.kotlin.delegates
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import java.util.concurrent.locks.ReentrantLock
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import kotlin.concurrent.withLock
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interface Producer {
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fun produce(): String
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}
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class ProducerImpl : Producer {
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override fun produce() = "ProducerImpl"
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}
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class EnhancedProducer(private val delegate: Producer) : Producer by delegate {
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override fun produce() = "${delegate.produce()} and EnhancedProducer"
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}
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interface MessageService {
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fun processMessage(message: String): String
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}
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class MessageServiceImpl : MessageService {
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override fun processMessage(message: String): String {
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return "MessageServiceImpl: $message"
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}
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}
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interface UserService {
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fun processUser(userId: String): String
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}
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class UserServiceImpl : UserService {
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override fun processUser(userId: String): String {
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return "UserServiceImpl: $userId"
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}
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}
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class CompositeService : UserService by UserServiceImpl(), MessageService by MessageServiceImpl()
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interface Service {
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val seed: Int
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fun serve(action: (Int) -> Unit)
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}
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class ServiceImpl : Service {
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override val seed = 1
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override fun serve(action: (Int) -> Unit) {
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action(seed)
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}
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}
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class ServiceDecorator : Service by ServiceImpl() {
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override val seed = 2
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}
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@@ -0,0 +1,6 @@
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package com.baeldung.kotlin.delegates
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class User(val id: Int) {
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var name: String by DatabaseDelegate("name", id)
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var age: Int by DatabaseDelegate("age", id)
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}
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@@ -0,0 +1,143 @@
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package com.baeldung.kotlin
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import org.junit.Test
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import kotlin.test.assertEquals
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import kotlin.test.assertTrue
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class GenericsTest {
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@Test
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fun givenParametrizeClass_whenInitializeItWithSpecificType_thenShouldBeParameterized() {
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//given
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val parameterizedClass = ParameterizedClass<String>("string-value")
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//when
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val res = parameterizedClass.getValue()
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//then
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assertTrue(res is String)
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}
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@Test
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fun givenParametrizeClass_whenInitializeIt_thenShouldBeParameterizedByInferredType() {
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//given
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val parameterizedClass = ParameterizedClass("string-value")
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//when
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val res = parameterizedClass.getValue()
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//then
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assertTrue(res is String)
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}
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@Test
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fun givenParameterizedProducerByOutKeyword_whenGetValue_thenCanAssignItToSuperType() {
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//given
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val parameterizedProducer = ParameterizedProducer("string")
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//when
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val ref: ParameterizedProducer<Any> = parameterizedProducer
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//then
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assertTrue(ref is ParameterizedProducer<Any>)
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}
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@Test
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fun givenParameterizedConsumerByInKeyword_whenGetValue_thenCanAssignItToSubType() {
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//given
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val parameterizedConsumer = ParameterizedConsumer<Number>()
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//when
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val ref: ParameterizedConsumer<Double> = parameterizedConsumer
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//then
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assertTrue(ref is ParameterizedConsumer<Double>)
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}
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@Test
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fun givenTypeProjections_whenOperateOnTwoList_thenCanAcceptListOfSubtypes() {
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//given
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val ints: Array<Int> = arrayOf(1, 2, 3)
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val any: Array<Any?> = arrayOfNulls(3)
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//when
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copy(ints, any)
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//then
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assertEquals(any[0], 1)
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assertEquals(any[1], 2)
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assertEquals(any[2], 3)
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}
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fun copy(from: Array<out Any>, to: Array<Any?>) {
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assert(from.size == to.size)
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for (i in from.indices)
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to[i] = from[i]
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}
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@Test
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fun givenTypeProjection_whenHaveArrayOfIn_thenShouldAddElementsOfSubtypesToIt() {
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//given
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val objects: Array<Any?> = arrayOfNulls(1)
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//when
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fill(objects, 1)
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//then
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assertEquals(objects[0], 1)
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}
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fun fill(dest: Array<in Int>, value: Int) {
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dest[0] = value
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}
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@Test
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fun givenStartProjection_whenPassAnyType_thenCompile() {
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//given
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val array = arrayOf(1,2,3)
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//then
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printArray(array)
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}
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fun printArray(array: Array<*>) {
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array.forEach { println(it) }
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}
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@Test
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fun givenFunctionWithDefinedGenericConstraints_whenCallWithProperType_thenCompile(){
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//given
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val listOfInts = listOf(5,2,3,4,1)
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//when
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val sorted = sort(listOfInts)
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//then
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assertEquals(sorted, listOf(1,2,3,4,5))
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}
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fun <T: Comparable<T>> sort(list: List<T>): List<T>{
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return list.sorted()
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}
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class ParameterizedClass<A>(private val value: A) {
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fun getValue(): A {
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return value
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}
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}
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class ParameterizedProducer<out T>(private val value: T) {
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fun get(): T {
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return value
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}
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}
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class ParameterizedConsumer<in T> {
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fun toString(value: T): String {
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return value.toString()
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}
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}
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}
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@@ -0,0 +1,26 @@
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package com.baeldung.kotlin.delegates
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import org.junit.Test
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import kotlin.test.assertEquals
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class DatabaseDelegatesTest {
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@Test
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fun testGetKnownFields() {
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val user = User(1)
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assertEquals("George", user.name)
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assertEquals(4, user.age)
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}
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@Test
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fun testSetKnownFields() {
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val user = User(2)
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user.age = 3
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assertEquals(3, user.age)
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}
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@Test(expected = NoRecordFoundException::class)
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fun testGetKnownField() {
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val user = User(3)
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user.name
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}
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}
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@@ -0,0 +1,28 @@
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package com.baeldung.kotlin.delegates
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import org.assertj.core.api.Assertions.assertThat
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import org.junit.Test
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class InterfaceDelegationTest {
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@Test
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fun `when delegated implementation is used then it works as expected`() {
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val producer = EnhancedProducer(ProducerImpl())
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assertThat(producer.produce()).isEqualTo("ProducerImpl and EnhancedProducer")
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}
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@Test
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fun `when composite delegation is used then it works as expected`() {
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val service = CompositeService()
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assertThat(service.processMessage("message")).isEqualTo("MessageServiceImpl: message")
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assertThat(service.processUser("user")).isEqualTo("UserServiceImpl: user")
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}
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@Test
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fun `when decoration is used then delegate knows nothing about it`() {
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val service = ServiceDecorator()
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service.serve {
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assertThat(it).isEqualTo(1)
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}
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}
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}
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