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Kotlin’s Advanced Language Features

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High Order Function's Extension

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fun String.blowUp() { boom() } "Nooooo".blowUp()

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fun buildString( builderAction: (StringBuilder) -> Unit ): String {a }b fun main(args: Array) {c }e

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fun buildString( builderAction: (StringBuilder) -> Unit ): String {a val sb = StringBuilder() builderAction(sb) return sb.toString() }b fun main(args: Array) {c }e

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fun buildString( builderAction: (StringBuilder) -> Unit ): String {a val sb = StringBuilder() builderAction(sb) return sb.toString() }b fun main(args: Array) {c val s = buildString({ stringBuilder -> stringBuilder.append("Hello, ") stringBuilder.append("World!") })d }e

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fun buildString( builderAction: (StringBuilder) -> Unit ): String {a val sb = StringBuilder() builderAction(sb) return sb.toString() }b fun main(args: Array) {c val s = buildString { stringBuilder -> stringBuilder.append("Hello, ") stringBuilder.append("World!") }d }e

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fun buildString( builderAction: (StringBuilder) -> Unit ): String {a val sb = StringBuilder() builderAction(sb) return sb.toString() }b fun main(args: Array) {c val s = buildString { it.append("Hello, ") it.append("World!") }d }e

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fun buildString( builderAction: (StringBuilder) -> Unit ): String {a val sb = StringBuilder() builderAction(sb) return sb.toString() }b fun main(args: Array) {c val s = buildString { append("Hello, ") append("World!") }d }e

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fun buildString( builderAction: StringBuilder.() -> Unit ): String {a val sb = StringBuilder() builderAction(sb) return sb.toString() }b fun main(args: Array) {c val s = buildString { append("Hello, ") append("World!") }d }e

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fun buildString( builderAction: StringBuilder.() -> Unit ): String {a val sb = StringBuilder() sb.builderAction() return sb.toString() }b fun main(args: Array) {c val s = buildString { append("Hello, ") append("World!") }d }e

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fun buildString( builderAction: StringBuilder.() -> Unit ): String {a val sb = StringBuilder() sb.builderAction() return sb.toString() }b fun main(args: Array) {c val s = buildString { append("Hello, ") append("World!") }d }e

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fun buildString( builderAction: StringBuilder.() -> Unit ): String {a val sb = StringBuilder() sb.builderAction() return sb.toString() }b fun main(args: Array) {c val s = buildString { this.append("Hello, ") append("World!") }d }e

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val taco = Taco() with(taco) { println(name) println(tasty) }

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fun with( receiver: T, block: T.() -> R ): R { return receiver.block() }

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When do we seal the casting?

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interface BinaryNumber object Zero : BinaryNumber object One : BinaryNumber

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interface BinaryNumber object Zero : BinaryNumber object One : BinaryNumber fun BinaryNumber.toInt():Int {a return when (this) {b is One -> 1 is Zero -> 0 else -> throw IllegalStateException() }c }d

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interface BinaryNumber object Zero : BinaryNumber object One : BinaryNumber fun BinaryNumber.toInt():Int {a return when (this) {b is One -> 1 is Zero -> 0 }c }d

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interface BinaryNumber object Zero : BinaryNumber object One : BinaryNumber fun BinaryNumber.toInt():Int {a return when (this) {b is One -> 1 is Zero -> 0 else -> throw IllegalStateException() }c }d

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interface BinaryNumber object Zero : BinaryNumber object One : BinaryNumber class Magic() : BinaryNumber() { fun abracadabra() { // ... } } fun BinaryNumber.toInt():Int {a return when (this) {b is One -> 1 is Zero -> 0 else -> throw IllegalStateException() }c }d

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interface BinaryNumber object Zero : BinaryNumber object One : BinaryNumber fun BinaryNumber.toInt():Int {a return when (this) {b is One -> 1 is Zero -> 0 else -> throw IllegalStateException() }c }d

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sealed class BinaryNumber object Zero : BinaryNumber() object One : BinaryNumber() fun BinaryNumber.toInt():Int {a return when (this) {b is One -> 1 is Zero -> 0 else -> throw IllegalStateException() }c }d

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sealed class BinaryNumber object Zero : BinaryNumber() object One : BinaryNumber() fun BinaryNumber.toInt():Int {a return when (this) {b is One -> 1 is Zero -> 0 }c }d

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sealed class BinaryNumber object Zero : BinaryNumber() object One : BinaryNumber() class Magic() : BinaryNumber() {z fun abracadabra() {w // ... }t }r fun BinaryNumber.toInt():Int {a return when (this) {b is One -> 1 is Zero -> 0 }c }d

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sealed class BinaryNumber object Zero : BinaryNumber() object One : BinaryNumber() class Magic() : BinaryNumber() {z fun abracadabra() {w // ... }t }r fun BinaryNumber.toInt():Int {a return when (this) {b is One -> 1 is Zero -> 0 }c }d

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sealed class BinaryNumber object Zero : BinaryNumber() object One : BinaryNumber() class Magic() : BinaryNumber() {z fun abracadabra() {w // ... }t }r fun BinaryNumber.toInt():Int {a return when (this) {b is One -> 1 is Zero -> 0 is Magic -> this.abracadabra() }c }d

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sealed class BinaryNumber object Zero : BinaryNumber() object One : BinaryNumber() class Magic() : BinaryNumber() { fun abracadabra() { // ... } } fun BinaryNumber.toInt():Int {a return when (this) {b is One -> 1 is Zero -> 0 is Magic -> this.abracadabra() }c }d

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fun requireNotNull(obj: Any?) {a if (obj == null) throw IllegalArgumentException() }d

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fun requireNotNull(obj: Any?) {a if (obj == null) throw IllegalArgumentException() }d fun foo(s: String?) {e requireNotNull(s) s.length }f

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fun requireNotNull(obj: Any?) {a contract { returns() implies (obj != null) }c if (obj == null) throw IllegalArgumentException() }d fun foo(s: String?) {e requireNotNull(s) s.length }f

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Error is Ever the Sequence of Haste

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people // List

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people // List .map(People::name) .filter { it.startsWith("J") }

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people // List .map(People::name) // List .filter { it.startsWith("J") } // List

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people // List .asSequence() .map(People::name) .filter { it.startsWith("J") }

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people // List .asSequence() // Sequence .map(People::name) // Sequence .filter { it.startsWith("J") } // Sequence

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people // List .asSequence() // Sequence .map(People::name) // Sequence .filter { it.startsWith("J") } // Sequence .toList() // List

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people .map(People::name) .find { it.startsWith("J") }

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people .map(People::name) .find { it.startsWith("J") } And Car Jes Wil Pir A C J W P A C J

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people.asSequence() .map(People::name) .find { it.startsWith("J") } And Car Jes Wil Pir A C J A C J

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Generics at runtime

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fun sumUp(items: Collection<*>) {a if (items is List) {d println(ints.sum()) }b }c val strings: List = listOf("a", "b") sumUp(strings)

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fun sumUp(items: Collection<*>) {a if (items is List) {d println(ints.sum()) }b }c val strings: List = listOf("a", "b") sumUp(strings)

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fun sumUp(items: Collection<*>) {a val ints = items as? List ?: return println("We got a list of ints") println(ints.sum()) }c val strings: List = listOf("a", "b") sumUp(strings)

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fun sumUp(items: Collection<*>) {a val ints = items as? List ?: return println("We got a list of ints") println(ints.sum()) }c val strings: List = listOf("a", "b") sumUp(strings) ----- We got a list of ints Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Number

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fun sumUp(items: Collection<*>) {a val ints = items as? List ?: return println("We got a list of ints") println(ints.sum()) }c val strings: List = listOf("a", "b") sumUp(strings)

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fun sumUp(items: Collection) {a val ints = items as? List ?: return println("We got a list of ints") println(ints.sum()) }c val strings: List = listOf("a", "b") sumUp(strings)

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fun Iterable<*>.filterIsInstance(): List {a val destination = mutableListOf() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f

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fun Iterable<*>.filterIsInstance(): List {a val destination = mutableListOf() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f listOf("a", 1, 0x0, 2L, 'u') .filterIsInstance()

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fun Iterable<*>.filterIsInstance(): List {a val destination = mutableListOf() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f listOf("a", 1, 0x0, 2L, 'u') .filterIsInstance()

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fun Iterable<*>.filterIsInstance(): List {a val destination = mutableListOf() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f listOf("a", 1, 0x0, 2L, 'u') .filterIsInstance()

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fun Iterable<*>.filterIsInstance(): List {a val destination = mutableListOf() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f

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fun Iterable<*>.filterIsInstance(): List {a val destination = mutableListOf() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f

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inline fun Iterable<*>.filterIsInstance(): List {a val destination = mutableListOf() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f

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inline fun Iterable<*>.filterIsInstance(): List val destination = mutableListOf() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f

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inline fun Iterable<*>.filterIsInstance(): List val destination = mutableListOf() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f

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inline fun Iterable<*>.filterIsInstance(): List val destination = mutableListOf() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f listOf("a", 1, 0x0, 2L, 'u') .filterIsInstance()

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val moshi = Moshi.Builder().build() moshi.adapter(String::class.java) // JsonAdapter

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val moshi = Moshi.Builder().build() moshi.adapter(String::class.java)

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val moshi = Moshi.Builder().build() moshi.adapter()

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inline fun Moshi.adapter(): JsonAdapter {a return this.adapter(T::class.java) }b val moshi = Moshi.Builder().build() moshi.adapter()

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If you really want to grow as a Klass, you've got to learn to delegate

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class canTbeextended open class canbeextended

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class CountingSet( val innerSet: MutableCollection = HashSet() ) : MutableCollection {abcdefgh }t

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class CountingSet( val innerSet: MutableCollection = HashSet() ) : MutableCollection {abcdefgh var objectsAdded = 0 }t

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class CountingSet( val innerSet: MutableCollection = HashSet() ) : MutableCollection {abcdefgh var objectsAdded = 0 override fun add(element: T): Boolean {w objectsAdded++ return innerSet.add(element) }p override fun addAll(c: Collection): Boolean {o objectsAdded += c.size return innerSet.addAll(c) }k }t

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class CountingSet( val innerSet: MutableCollection = HashSet() ) : MutableCollection {abcdefgh var objectsAdded = 0 override fun add(element: T): Boolean {w objectsAdded++ return innerSet.add(element) }p override fun addAll(c: Collection): Boolean {o objectsAdded += c.size return innerSet.addAll(c) }k }t

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class CountingSet( val innerSet: MutableCollection = HashSet() ) : MutableCollection {abcdefgh var objectsAdded = 0 override fun add(element: T): Boolean {w objectsAdded++ return innerSet.add(element) }p override fun addAll(c: Collection): Boolean {o objectsAdded += c.size return innerSet.addAll(c) }k override val size: Int get() = innerSet.size override fun contains(element: T): Boolean { return innerSet.contains(element) } override fun containsAll(elements: Collection): Boolean { return innerSet.containsAll(elements) } override fun isEmpty(): Boolean { return innerSet.isEmpty() } override fun clear() { innerSet.clear() } override fun iterator(): MutableIterator { return innerSet.iterator() } override fun remove(element: T): Boolean { return innerSet.remove(element) } override fun removeAll(elements: Collection): Boolean { return innerSet.removeAll(elements) } override fun retainAll(elements: Collection): Boolean { return innerSet.retainAll(elements) } }t

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class CountingSet( val innerSet: MutableCollection = HashSet() ) : MutableCollection {abcdefgh var objectsAdded = 0 override fun add(element: T): Boolean {w objectsAdded++ return innerSet.add(element) }p override fun addAll(c: Collection): Boolean {o objectsAdded += c.size return innerSet.addAll(c) }k }t

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class CountingSet( val innerSet: MutableCollection = HashSet() ) : MutableCollection by innerSet {abcdefgh var objectsAdded = 0 override fun add(element: T): Boolean {w objectsAdded++ return innerSet.add(element) }p override fun addAll(c: Collection): Boolean {o objectsAdded += c.size return innerSet.addAll(c) }k }t

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class CountingSet( val innerSet: MutableCollection = HashSet() ) : MutableCollection by innerSet {abcdefgh var objectsAdded = 0 override fun add(element: T): Boolean {w objectsAdded++ return innerSet.add(element) }p override fun addAll(c: Collection): Boolean {o objectsAdded += c.size return innerSet.addAll(c) }k }t

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class Foo { val data: Int by lazy { computeStuff() } } • lazy • observable • vetoable • notNull

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The Secret of Success of to Triple Your Quotes

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"""(.+)"(.+)"(.+)""".toRegex() new Regex("(.+)\"(.+)\"(.+)") "C:\\Users\\yole\\kotlin-book" """C:\Users\yole\kotlin-book""" """${'$'}99.9""" "\$99.9" "$99.9" Java Kotlin

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assertThat(toString(taco)).isEqualTo("" + "package com.squareup.tacos\n" + "\n" + "import kotlin.String\n" + "\n" + "class Taco {\n" + " final override fun toString(): String = \"taco\"\n" + "}\n" + "")c

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assertThat(toString(taco)).isEqualTo(""" package com.squareup.tacos import kotlin.String class Taco { final override fun toString(): String = "taco" }z """)c

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assertThat(toString(taco)).isEqualTo(""" package com.squareup.tacos import kotlin.String class Taco { final override fun toString(): String = "taco" }z """)c

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assertThat(toString(taco)).isEqualTo(""" |package com.squareup.tacos | |import kotlin.String | |class Taco { | final override fun toString(): String = "taco" |}z |""")c

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assertThat(toString(taco)).isEqualTo(""" |package com.squareup.tacos | |import kotlin.String | |class Taco { | final override fun toString(): String = "taco" |} |""".trimMargin())c

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And if you want these kind of dreams it's Deprecation

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class SomeList {a fun remove(index: Int) {b }c }f

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class SomeList {a fun remove(index: Int) {b }c fun removeAt(index: Int) {d }e }f

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class SomeList {a @Deprecated("Use removeAt(index) instead.")h fun remove(index: Int) {b }c fun removeAt(index: Int) {d }e }f

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class SomeList {a @Deprecated("Use removeAt(index) instead.", ReplaceWith("removeAt(index)"))h fun remove(index: Int) {b }c fun removeAt(index: Int) {d }e }f

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class SomeList {a @Deprecated("Use removeAt(index) instead.", ReplaceWith("removeAt(index)"))h fun remove(index: Int) {b }c fun removeAt(index: Int) {d }e }f

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Live Demo

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