Kotlin's Advanced Language Features

1. Kotlin’s Advanced Language Features
2. High Order Function's Extension
3. fun String.blowUp() { boom() } "Nooooo".blowUp()
4. fun buildString( builderAction: (StringBuilder) -> Unit ): String {a }b fun main(args: Array<String>) {c }e
5. fun buildString( builderAction: (StringBuilder) -> Unit ): String {a val sb = StringBuilder() builderAction(sb) return sb.toString() }b fun main(args: Array<String>) {c }e
6. fun buildString( builderAction: (StringBuilder) -> Unit ): String {a val sb = StringBuilder() builderAction(sb) return sb.toString() }b fun main(args: Array<String>) {c val s = buildString({ stringBuilder -> stringBuilder.append("Hello, ") stringBuilder.append("World!") })d }e
7. fun buildString( builderAction: (StringBuilder) -> Unit ): String {a val sb = StringBuilder() builderAction(sb) return sb.toString() }b fun main(args: Array<String>) {c val s = buildString { stringBuilder -> stringBuilder.append("Hello, ") stringBuilder.append("World!") }d }e
8. fun buildString( builderAction: (StringBuilder) -> Unit ): String {a val sb = StringBuilder() builderAction(sb) return sb.toString() }b fun main(args: Array<String>) {c val s = buildString { it.append("Hello, ") it.append("World!") }d }e
9. fun buildString( builderAction: (StringBuilder) -> Unit ): String {a val sb = StringBuilder() builderAction(sb) return sb.toString() }b fun main(args: Array<String>) {c val s = buildString { append("Hello, ") append("World!") }d }e
10. fun buildString( builderAction: StringBuilder.() -> Unit ): String {a val sb = StringBuilder() builderAction(sb) return sb.toString() }b fun main(args: Array<String>) {c val s = buildString { append("Hello, ") append("World!") }d }e
11. fun buildString( builderAction: StringBuilder.() -> Unit ): String {a val sb = StringBuilder() sb.builderAction() return sb.toString() }b fun main(args: Array<String>) {c val s = buildString { append("Hello, ") append("World!") }d }e
12. fun buildString( builderAction: StringBuilder.() -> Unit ): String {a val sb = StringBuilder() sb.builderAction() return sb.toString() }b fun main(args: Array<String>) {c val s = buildString { append("Hello, ") append("World!") }d }e
13. fun buildString( builderAction: StringBuilder.() -> Unit ): String {a val sb = StringBuilder() sb.builderAction() return sb.toString() }b fun main(args: Array<String>) {c val s = buildString { this.append("Hello, ") append("World!") }d }e
15. val taco = Taco() with(taco) { println(name) println(tasty) }
16. fun <T, R> with( receiver: T, block: T.() -> R ): R { return receiver.block() }
17. When do we seal the casting?
18. interface BinaryNumber object Zero : BinaryNumber object One : BinaryNumber
19. 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
20. 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
21. 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
22. 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
23. 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
24. 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
25. 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
26. 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
27. 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
28. 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
29. 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
31. fun requireNotNull(obj: Any?) {a if (obj == null) throw IllegalArgumentException() }d
32. fun requireNotNull(obj: Any?) {a if (obj == null) throw IllegalArgumentException() }d fun foo(s: String?) {e requireNotNull(s) s.length }f
33. 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
35. Error is Ever the Sequence of Haste
36. people // List<People>
37. people // List<People> .map(People::name) .filter { it.startsWith("J") }
38. people // List<People> .map(People::name) // List<People> .filter { it.startsWith("J") } // List<People>
39. people // List<People> .asSequence() .map(People::name) .filter { it.startsWith("J") }
40. people // List<People> .asSequence() // Sequence<People> .map(People::name) // Sequence<String> .filter { it.startsWith("J") } // Sequence<String>
41. people // List<People> .asSequence() // Sequence<People> .map(People::name) // Sequence<String> .filter { it.startsWith("J") } // Sequence<String> .toList() // List<People>
42. people .map(People::name) .find { it.startsWith("J") }
43. people .map(People::name) .find { it.startsWith("J") } And Car Jes Wil Pir A C J W P A C J
44. people.asSequence() .map(People::name) .find { it.startsWith("J") } And Car Jes Wil Pir A C J A C J
46. Generics at runtime
47. fun sumUp(items: Collection<*>) {a if (items is List<Int>) {d println(ints.sum()) }b }c val strings: List<String> = listOf("a", "b") sumUp(strings)
48. fun sumUp(items: Collection<*>) {a if (items is List<Int>) {d println(ints.sum()) }b }c val strings: List<String> = listOf("a", "b") sumUp(strings)
49. fun sumUp(items: Collection<*>) {a val ints = items as? List<Int> ?: return println("We got a list of ints") println(ints.sum()) }c val strings: List<String> = listOf("a", "b") sumUp(strings)
50. fun sumUp(items: Collection<*>) {a val ints = items as? List<Int> ?: return println("We got a list of ints") println(ints.sum()) }c val strings: List<String> = 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
51. fun sumUp(items: Collection<*>) {a val ints = items as? List<Int> ?: return println("We got a list of ints") println(ints.sum()) }c val strings: List<String> = listOf("a", "b") sumUp(strings)
52. fun sumUp(items: Collection<Int>) {a val ints = items as? List<Int> ?: return println("We got a list of ints") println(ints.sum()) }c val strings: List<String> = listOf("a", "b") sumUp(strings)
54. fun <T> Iterable<*>.filterIsInstance(): List<T> {a val destination = mutableListOf<T>() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f
55. fun <T> Iterable<*>.filterIsInstance(): List<T> {a val destination = mutableListOf<T>() 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<String>()
56. fun <T> Iterable<*>.filterIsInstance(): List<T> {a val destination = mutableListOf<T>() 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<Int>()
57. fun <T> Iterable<*>.filterIsInstance(): List<T> {a val destination = mutableListOf<T>() 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<Char>()
58. fun <T> Iterable<*>.filterIsInstance(): List<T> {a val destination = mutableListOf<T>() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f
60. fun <T> Iterable<*>.filterIsInstance(): List<T> {a val destination = mutableListOf<T>() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f
61. inline fun <T> Iterable<*>.filterIsInstance(): List<T> {a val destination = mutableListOf<T>() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f
62. inline fun <reified T> Iterable<*>.filterIsInstance(): List val destination = mutableListOf<T>() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f
63. inline fun <reified T> Iterable<*>.filterIsInstance(): List val destination = mutableListOf<T>() for (element in this) {c if (element is T) {d destination.add(element) }p }e return destination }f
64. inline fun <reified T> Iterable<*>.filterIsInstance(): List val destination = mutableListOf<T>() 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<String>()
66. val moshi = Moshi.Builder().build() moshi.adapter(String::class.java) // JsonAdapter<String>
67. val moshi = Moshi.Builder().build() moshi.adapter(String::class.java)
68. val moshi = Moshi.Builder().build() moshi.adapter<String>()
69. inline fun <reified T> Moshi.adapter(): JsonAdapter<T> {a return this.adapter(T::class.java) }b val moshi = Moshi.Builder().build() moshi.adapter<String>()
71. If you really want to grow as a Klass, you've got to learn to delegate
72. class canTbeextended open class canbeextended
73. class CountingSet<T>( val innerSet: MutableCollection<T> = HashSet() ) : MutableCollection<T> {abcdefgh }t
74. class CountingSet<T>( val innerSet: MutableCollection<T> = HashSet() ) : MutableCollection<T> {abcdefgh var objectsAdded = 0 }t
75. class CountingSet<T>( val innerSet: MutableCollection<T> = HashSet() ) : MutableCollection<T> {abcdefgh var objectsAdded = 0 override fun add(element: T): Boolean {w objectsAdded++ return innerSet.add(element) }p override fun addAll(c: Collection<T>): Boolean {o objectsAdded += c.size return innerSet.addAll(c) }k }t
76. class CountingSet<T>( val innerSet: MutableCollection<T> = HashSet() ) : MutableCollection<T> {abcdefgh var objectsAdded = 0 override fun add(element: T): Boolean {w objectsAdded++ return innerSet.add(element) }p override fun addAll(c: Collection<T>): Boolean {o objectsAdded += c.size return innerSet.addAll(c) }k }t
77. class CountingSet<T>( val innerSet: MutableCollection<T> = HashSet() ) : MutableCollection<T> {abcdefgh var objectsAdded = 0 override fun add(element: T): Boolean {w objectsAdded++ return innerSet.add(element) }p override fun addAll(c: Collection<T>): 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<T>): Boolean { return innerSet.containsAll(elements) } override fun isEmpty(): Boolean { return innerSet.isEmpty() } override fun clear() { innerSet.clear() } override fun iterator(): MutableIterator<T> { return innerSet.iterator() } override fun remove(element: T): Boolean { return innerSet.remove(element) } override fun removeAll(elements: Collection<T>): Boolean { return innerSet.removeAll(elements) } override fun retainAll(elements: Collection<T>): Boolean { return innerSet.retainAll(elements) } }t
78. class CountingSet<T>( val innerSet: MutableCollection<T> = HashSet() ) : MutableCollection<T> {abcdefgh var objectsAdded = 0 override fun add(element: T): Boolean {w objectsAdded++ return innerSet.add(element) }p override fun addAll(c: Collection<T>): Boolean {o objectsAdded += c.size return innerSet.addAll(c) }k }t
79. class CountingSet<T>( val innerSet: MutableCollection<T> = HashSet() ) : MutableCollection<T> by innerSet {abcdefgh var objectsAdded = 0 override fun add(element: T): Boolean {w objectsAdded++ return innerSet.add(element) }p override fun addAll(c: Collection<T>): Boolean {o objectsAdded += c.size return innerSet.addAll(c) }k }t
80. class CountingSet<T>( val innerSet: MutableCollection<T> = HashSet() ) : MutableCollection<T> by innerSet {abcdefgh var objectsAdded = 0 override fun add(element: T): Boolean {w objectsAdded++ return innerSet.add(element) }p override fun addAll(c: Collection<T>): Boolean {o objectsAdded += c.size return innerSet.addAll(c) }k }t
82. class Foo { val data: Int by lazy { computeStuff() } } • lazy • observable • vetoable • notNull
83. The Secret of Success of to Triple Your Quotes
84. """(.+)"(.+)"(.+)""".toRegex() new Regex("(.+)\"(.+)\"(.+)") "C:\\Users\\yole\\kotlin-book" """C:\Users\yole\kotlin-book""" """${'$'}99.9""" "\$99.9" "$99.9" Java Kotlin
85. 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
86. assertThat(toString(taco)).isEqualTo(""" package com.squareup.tacos import kotlin.String class Taco { final override fun toString(): String = "taco" }z """)c
87. assertThat(toString(taco)).isEqualTo(""" package com.squareup.tacos import kotlin.String class Taco { final override fun toString(): String = "taco" }z """)c
88. assertThat(toString(taco)).isEqualTo(""" |package com.squareup.tacos | |import kotlin.String | |class Taco { | final override fun toString(): String = "taco" |}z |""")c
89. assertThat(toString(taco)).isEqualTo(""" |package com.squareup.tacos | |import kotlin.String | |class Taco { | final override fun toString(): String = "taco" |} |""".trimMargin())c
91. And if you want these kind of dreams it's Deprecation
92. class SomeList {a fun remove(index: Int) {b }c }f
93. class SomeList {a fun remove(index: Int) {b }c fun removeAt(index: Int) {d }e }f
94. class SomeList {a @Deprecated("Use removeAt(index) instead.")h fun remove(index: Int) {b }c fun removeAt(index: Int) {d }e }f
95. 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
96. 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
97. Live Demo