New features in Kotlin 1.1 and what's next

This talk will be an introduction into Kotlin new features which will be released in version 1.1. We will consider use-cases and real examples where applying new features will make your code more precise and brief. We will also talk about our future plans concerning further development of Kotlin.

Transcript

1. New features in Kotlin 1.1 and what's next Stanislav.Erokhin@JetBrains.com
2. Current versions 1.1 1.0 1.0.1 1.0.2 1.0.3 1.0.4 1.1-M1 1.1-M2
3. Destructuring data class Person( val name: String, val city: String ) fun getPerson(): Person { return Person("John", "London") } fun sayHello() { val (name, city) = getPerson() println("Hello $name from $city") }
4. Destructuring data class Person( val name: String, val city: String ) fun getPerson(): Person { return Person("John", "London") } fun sayHello() { val (name, city) = getPerson() println("Hello $name from $city") }
5. Destructuring data class Person( val name: String, val city: String ) fun getPerson(): Person { return Person("John", "London") } fun sayHello() { val (name, city) = getPerson() println("Hello $name from $city") }
6. Destructuring fun helloAll(nameToCity: Map<String, String>) { for (entry in nameToCity) { println("Hello ${entry.key} from ${entry.value}") } } fun helloAll(nameToCity: Map<String, String>) { for ((name, city) in nameToCity) { println("Hello $name from $city") } }
7. Destructuring fun helloAll(nameToCity: Map<String, String>) { for (entry in nameToCity) { println("Hello ${entry.key} from ${entry.value}") } } fun helloAll(nameToCity: Map<String, String>) { for ((name, city) in nameToCity) { println("Hello $name from $city") } }
8. Destructuring for lambdas data class Person( val name: String, val city: String, val age: Int ) fun sayHelloToChildren(persons: List<Person>) { val children = persons.filter { person -> person.age < 18 } children.forEach { (name, city) -> println("Hello $name from $city") } }
9. Destructuring for lambdas data class Person( val name: String, val city: String, val age: Int ) fun sayHelloToChildren(persons: List<Person>) { val children = persons.filter { person -> person.age < 18 } children.forEach { (name, city) -> println("Hello $name from $city") } }
10. Underscore for unused parameters fun addListener( listener: (String, Int, error: String?) -> Unit ) { … } … addListener { data, code, error -> if (error != null) println(error) }
11. Underscore for unused parameters fun addListener( listener: (String, Int, error: String?) -> Unit ) { … } … addListener { _, _, error -> if (error != null) println(error) }
12. Underscore for unused parameters data class Person( val name: String, val city: String, val age: Int ) val persons: List<Person> = … persons.forEach { (name, _, age) -> println("$name is $age years old") }
13. Data classes data class Person( val name: String, val city: String, val age: Int ) Generated methods: • toString • equals / hashCode • componentN • copy
14. Sealed classes sealed class Expr { class Num(val value: Int): Expr() class Sum(val left: Expr, val right: Expr): Expr() } fun eval(e: Expr): Int { when (e) { is Expr.Num -> return e.value is Expr.Sum -> return eval(e.left) + eval(e.right) } }
15. Sealed & data classes sealed data 1.0
16. Sealed & data classes sealed data 1.1
17. Sealed & data classes sealed class Expr { class Num(val value: Int): Expr() data class Sum( val left: Expr, val right: Expr ): Expr() } sealed data 1.1
18. Type aliases fun foo( data: String, handler: (Int, String, Any) -> Unit ) { … } fun bar( code: Int, handler: (Int, String, Any) -> Unit ) { … } fun baz( obj: Any, handler: (Int, String, Any) -> Unit ) { … }
19. Type aliases fun foo( data: String, handler: (Int, String, Any) -> Unit ) { … } fun bar( code: Int, handler: (Int, String, Any) -> Unit ) { … } fun baz( obj: Any, handler: (Int, String, Any) -> Unit ) { … }
20. Type aliases typealias MyHandler = (Int, String, Any) -> Unit fun foo(data: String, handler: MyHandler) { … } fun bar(code: Int, handler: MyHandler) { … } fun baz(obj: Any, handler: MyHandler) { … }
21. Type aliases typealias MyHandler = (Int, String, Any) -> Unit fun foo(data: String, handler: MyHandler) { … } fun bar(code: Int, handler: MyHandler) { … } fun baz(obj: Any, handler: MyHandler) { … }
22. Type aliases typealias MyString = String fun foo(s: MyString) = println(s) fun bar(s: String) = foo(s)
23. Type aliases typealias MyString = String fun foo(s: MyString) = println(s) fun bar(s: String) = foo(s) Same type
24. Type aliases typealias MyString = String fun foo(s: MyString) = println(s) fun bar(s: String) = foo(s) Same type
25. Type aliases typealias MyHandler = (Int, String, Any) -> Unit typealias Predicate<T> = (T) -> Boolean typealias NodeSet = Set<Node> typealias FileTable<K> = Map<K, List<File>> typealias EdgeMap<N> = Map<N, List<N>>
26. Asynchronous computations loadImage().whenComplete { image -> panel.setImage(image) }
27. Asynchronous computations loadImage().whenComplete { image -> panel.setImage(image) } IO Thread
28. Asynchronous computations loadImage().whenComplete { image -> panel.setImage(image) } IO Thread EDT Thread
29. Asynchronous computations loadImage().whenComplete { image -> resize(image).whenComplete { resizedImage -> panel.setImage(resizedImage) } } IO Thread EDT Thread
30. Asynchronous computations loadImage().whenComplete { image -> resize(image).whenComplete { resizedImage -> panel.setImage(resizedImage) } } IO Thread EDT Thread Other thread
31. Callback Hell *https://josephlin55555.files.wordpress.com/2015/12/screen-shot-2015-12-29-at-6-28-45-pm.png
32. Callback Hell *https://josephlin55555.files.wordpress.com/2015/12/screen-shot-2015-12-29-at-6-28-45-pm.png
33. Coroutines loadImage().whenComplete { panel.setImage(image) }
34. Coroutines loadImage().whenComplete { panel.setImage(image) } Time-consuming operation
35. Coroutines loadImage().whenComplete { panel.setImage(image) } Time-consuming operation Callback
36. Coroutines asyncUI { val image = await(loadImage()) panel.setImage(image) } loadImage().whenComplete { panel.setImage(image) } Time-consuming operation Callback
37. Coroutines asyncUI { val image = await(loadImage()) panel.setImage(image) } loadImage().whenComplete { panel.setImage(image) } Time-consuming operation Callback
38. Coroutines asyncUI { val image = await(loadImage()) panel.setImage(image) } loadImage().whenComplete { panel.setImage(image) } Time-consuming operation Continuation Callback
39. Coroutines asyncUI { val image = await(loadImage()) panel.setImage(image) } loadImage().whenComplete { panel.setImage(image) } Time-consuming operation Continuation Callback Suspending call
40. Coroutines asyncUI { val image = await(loadImage()) panel.setImage(image) } loadImage().whenComplete { panel.setImage(image) } Time-consuming operation Continuation Suspending call Callback
41. Coroutines asyncUI { val image = await(loadImage()) panel.setImage(image) } loadImage().whenComplete { panel.setImage(image) } Time-consuming operation Continuation Suspending call Callback Coroutine
42. Coroutines loadImage().whenComplete { image -> resize(image).whenComplete { resizedImage -> panel.setImage(resizedImage) } } asyncUI { val image = await(loadImage()) val resizedImage = await(resize(image)) panel.setImage(image) }
43. Coroutines loadImage().whenComplete { image -> resize(image).whenComplete { resizedImage -> panel.setImage(resizedImage) } } asyncUI { val image = await(loadImage()) val resizedImage = await(resize(image)) panel.setImage(image) } Suspending calls
44. C# Way async Task<String> work() { Thread.sleep(200); return "done"; } async Task moreWork() { Console.WriteLine("Work started"); var str = await work(); Console.WriteLine($"Work completed: {str}"); }
45. C# Way async Task<String> work() { Thread.sleep(200); return "done"; } async Task moreWork() { Console.WriteLine("Work started"); var str = await work(); Console.WriteLine($"Work completed: {str}"); }
46. C# Way async Task<String> work() { Thread.sleep(200); return "done"; } async Task moreWork() { Console.WriteLine("Work started"); var str = await work(); Console.WriteLine($"Work completed: {str}"); }
47. Kotlin Way fun work()/*: CompletableFuture<String>*/ = async { Thread.sleep(200) "done" } fun moreWork() = async { println("Work started") val str = await(work()) println("Work completed: $str") }
48. Kotlin Way fun work()/*: CompletableFuture<String>*/ = async { Thread.sleep(200) "done" } fun moreWork() = async { println("Work started") val str = await(work()) println("Work completed: $str") }
49. Kotlin Way fun work()/*: CompletableFuture<String>*/ = async { Thread.sleep(200) "done" } fun moreWork() = async { println("Work started") val str = await(work()) println("Work completed: $str") }
50. Library code: await() fun work(): CompletableFuture<String> = … fun moreWork() = async { println("Work started") val str = await(work()) println("Work completed: $str") }
51. Library code: await() fun work(): CompletableFuture<String> = … fun moreWork() = async { println("Work started") val str = await(work()) println("Work completed: $str") } suspend fun <V> await(f: CompletableFuture<V>, machine: Continuation<V>) { f.whenComplete { value, throwable -> if (throwable == null) machine.resume(value) else machine.resumeWithException(throwable) } }
52. Library code: await() fun work(): CompletableFuture<String> = … fun moreWork() = async { println("Work started") val str = await(work()) println("Work completed: $str") } suspend fun <V> await(f: CompletableFuture<V>, machine: Continuation<V>) { f.whenComplete { value, throwable -> if (throwable == null) machine.resume(value) else machine.resumeWithException(throwable) } }
53. Library code: await() fun work(): CompletableFuture<String> = … fun moreWork() = async { println("Work started") val str = await(work()) println("Work completed: $str") } suspend fun <V> await(f: CompletableFuture<V>, machine: Continuation<V>) { f.whenComplete { value, throwable -> if (throwable == null) machine.resume(value) else machine.resumeWithException(throwable) } }
54. Library code: await() fun work(): CompletableFuture<String> = … fun moreWork() = async { println("Work started") val str = await(work()) println("Work completed: $str") } suspend fun <V> await(f: CompletableFuture<V>, machine: Continuation<V>) { f.whenComplete { value, throwable -> if (throwable == null) machine.resume(value) else machine.resumeWithException(throwable) } }
55. Library code: await() fun work(): CompletableFuture<String> = … fun moreWork() = async { println("Work started") val str = await(work()) println("Work completed: $str") } suspend fun <V> await(f: CompletableFuture<V>, machine: Continuation<V>) { f.whenComplete { value, throwable -> if (throwable == null) machine.resume(value) else machine.resumeWithException(throwable) } }
56. Generators fun main(args: Array<String>) { val sequence/*: Sequence<Int>*/ = generate { yield(1) yield(2) for (i in 3..5) { yield(i) } yield(6) } println(sequence.joinToString()) }
57. Generators fun main(args: Array<String>) { val sequence/*: Sequence<Int>*/ = generate { yield(1) yield(2) for (i in 3..5) { yield(i) } yield(6) } println(sequence.joinToString()) } suspend calls
58. Summary: coroutines • Asynchronous programming - async/await and more • Lazy generators - yield • Maximum flexibility for library designers • Example library: - https://github.com/Kotlin/kotlinx.coroutines
59. Delegated properties 1 class Foo { 2 private var text: String? = null 3 4 private fun computeText(): String { … } 5 6 fun getText(): String { 7 if (text == null) { 8 text = computeText() 9 } 10 return text!! 11 } 12 }
60. Delegated properties class Foo { val text: String by lazy { computeText() } private fun computeText(): String { … } }
61. Delegated properties class Foo { val text/*: String*/ by lazy { … } } class OldFoo { private var text: String? = null private fun computeText(): String { … } fun getText(): String { if (text == null) { text = computeText() } return text!! } }
62. Delegated properties class Foo { val text/*: String*/ by lazy { … } } class OldFoo { private var text: String? = null private fun computeText(): String { … } fun getText(): String { if (text == null) { text = computeText() } return text!! } }
63. Delegated properties interface ResourceLoader<T> { operator fun getValue( thisRef: Any?, property: KProperty<*> ): T } fun <T> bindResource( id: ResourceID<T> ): ResourceLoader<T> { ... } class MyUI { val image by bindResource(image_id) val text by bindResource(text_id) }
64. Delegated properties interface ResourceLoader<T> { operator fun getValue( thisRef: Any?, property: KProperty<*> ): T } fun <T> bindResource( id: ResourceID<T> ): ResourceLoader<T> { ... } class MyUI { val image by bindResource(image_id) val text by bindResource(text_id) }
65. Delegated properties interface ResourceLoader<T> { operator fun getValue( thisRef: Any?, property: KProperty<*> ): T } fun <T> bindResource( id: ResourceID<T> ): ResourceLoader<T> { ... } class MyUI { val image by bindResource(image_id) val text by bindResource(text_id) }
66. Local delegated properties fun main(args: Array<String>) { val text by lazy { "Hello world!" } if (Math.random() > 0.5) { println(text) } }
67. Class Literal class Foo fun bar(n: Number) { val fooClass = Foo::class val kclass = n::class println(fooClass.simpleName) // "Foo" println(kClass.simpleName) // "Int" } fun main(args: Array<String>) = bar(4)
68. Member reference data class Person( val name: String, val city: String ) fun doSomething(persons: List<Person>) { val names = persons.map(Person::name) … } persons.map { p -> p.name }
69. Member reference data class Person( val name: String, val city: String ) fun doSomething(persons: List<Person>) { val names = persons.map(Person::name) … } persons.map { p -> p.name }
70. Member reference data class Person( val name: String, val city: String ) fun doSomething(persons: List<Person>) { val names = persons.map(Person::name) … } persons.map { p -> p.name } KProperty1<Person, String>
71. Bound member reference data class Person(val name: String) fun doSomething(person: Person) { val kProp = person::name computeAndPrint(kProp) // "Ivan" println(kProp()) // "Ivan" } fun computeAndPrint(c: () -> String) = println(c()) doSomething(Person("Ivan"))
72. Bound member reference data class Person(val name: String) fun doSomething(person: Person) { val kProp = person::name computeAndPrint(kProp) // "Ivan" println(kProp()) // "Ivan" } fun computeAndPrint(c: () -> String) = println(c()) doSomething(Person("Ivan")) KProperty0<String>
73. Bound member references class MyModel { fun initialize(button: JButton) { button.addActionListener(this::buttonAction) } fun buttonAction(e: ActionEvent) { … } }
74. JDK Collections interface List<E> { E get(int index) E set(int index, E element) } /* Read Only */ List<String> getNames() { List<String> l = …; return unmodifiableList(l); } getNames().set(1, "Ivan")
75. JDK Collections interface List<E> { E get(int index) E set(int index, E element) } /* Read Only */ List<String> getNames() { List<String> l = …; return unmodifiableList(l); } getNames().set(1, "Ivan")
76. JDK Collections interface List<E> { E get(int index) E set(int index, E element) } /* Read Only */ List<String> getNames() { List<String> l = …; return unmodifiableList(l); } getNames().set(1, "Ivan")
77. JDK Collections interface List<E> { E get(int index) E set(int index, E element) } /* Read Only */ List<String> getNames() { List<String> l = …; return unmodifiableList(l); } getNames().set(1, "Ivan") UnsupportedOperationException
78. Cool Collections interface List<E> { E get(int index) } interface MutableList<E> extends List<E> { E set(int index, E element) } List<String> getNames() { List<String> l = …; return l; // may be mutable } getNames().set(1, "Ivan")
79. Cool Collections interface List<E> { E get(int index) } interface MutableList<E> extends List<E> { E set(int index, E element) } List<String> getNames() { List<String> l = …; return l; // may be mutable } getNames().set(1, "Ivan")
80. Cool Collections interface List<E> { E get(int index) } interface MutableList<E> extends List<E> { E set(int index, E element) } List<String> getNames() { List<String> l = …; return l; // may be mutable } getNames().set(1, "Ivan") Compilation Error
81. Kotlin Collections Iterable<out T> Iterable<out T> Collection<out T> Collection<out T> List<out T> List<out T> Set<out T> Set<out T> MutableIterable<T> MutableIterable<T> MutableCollection<T> MutableCollection<T> MutableList<T> MutableList<T> MutableSet<T> MutableSet<T> java.lang.ArrayList<T> java.lang.ArrayList<T> java.util.HashSet<T> java.util.HashSet<T>
82. Java 8 default methods fun test(c: Collection<Int>) { c.stream() }
83. Java 8 default methods fun test(c: Collection<Int>) { c.stream() } kotlin.collections.Collection
84. Java 8 default methods fun test(c: Collection<Int>) { c.stream() } kotlin.collections.Collection java.util.Collection.stream
85. Java 8 default methods package java.util interface Collection<E> { default Stream<E> stream() { … } } package kotlin.collections interface Collection<out E> { fun stream(): Stream<E> { … } }
86. Java 8 default methods package java.util interface Collection<E> { default Stream<E> stream() { … } } package kotlin.collections interface Collection<out E> { fun stream(): Stream<E> { … } }
87. Java 8 default methods fun test(c: Collection<Int>) { c.stream() } kotlin.collections.Collection.stream
88. References • https://kotlinlang.org/ • Language Design Proposals (KEEP) – https://github.com/Kotlin/KEEP – Give your feedback in GitHub Issues • Issue tracker – https://youtrack.jetbrains.com/issues/KT
89. Thanks!
90. 1.0.x 1.0.y 1.1.x 1.1.y 1.2.x 1.2.y Compatibility
91. Migration to new version * https://media.licdn.com/mpr/mpr/shrinknp_800_800/AAEAAQAAAAAAAAckAAAAJDIyY2RmMDgyLTRlMTgtNDM3ZC1hZTczLTRjZGJlZWUyMWM3OQ.png 1.0 1.0 1.1 1.0 1.0
92. Migration to new version * https://media.licdn.com/mpr/mpr/shrinknp_800_800/AAEAAQAAAAAAAAckAAAAJDIyY2RmMDgyLTRlMTgtNDM3ZC1hZTczLTRjZGJlZWUyMWM3OQ.png 1.0 1.0 1.1 1.0 1.0 -language-version=1.0
93. JVM Target interface A { fun foo() {} } -jvm-target=1.8 // ===A.class== // class version 52.0 (52) public abstract interface A { // access flags 0x1 public default foo()V … }
94. Library code: async() fun work()/*: CompletableFuture<String>*/ = … fun moreWork() = async { println("Work started") val str = await(work()) println("Work completed: $str") } fun <T> async( coroutine c: FutureController<T>.() → Continuation<Unit> ): CompletableFuture<T> { val controller = FutureController<T>() c(controller).resume(Unit) return controller.future }