01 Kotlin Programming Language. What it is all about. Roman Belov, PMM in Kotlin

Transcript

1. Kotlin. Что это и зачем? — Роман Белов, PMM at Kotlin JetBrains Open Day Moscow
2. WHO R U?
3. В разделе личные качества стоит только одно слово: Прагматичен
4. “We’ve built tools to support so many nice languages, and we’re still using Java” JetBrains, 2010
5. Hello Kotlin!
6. • Kotlin is a modern language for JVM, JS and Native • Statically-typed • Object-oriented and functional paradigms • Open source under Apache 2.0 • Ver 1.0 in 2016 • Compatibility commitment • Now at version 1.2
7. Kotlin on Android
9. Gradle Script Kotlin
10. …
11. Server Android iOS Browser Kotlin/JVM Kotlin/JVM Kotlin/Native Kotlin/JS Multiplatform projects
12. fun main(args: Array<String>): Unit { println("Hello, World!") } > Hello, World!
13. fun main(args: Array<String>): Unit { println("Hello, World!") } Function keyword
14. fun main(args: Array<String>): Unit { println("Hello, World!") } Function name
15. fun main(args: Array<String>): Unit { println("Hello, World!") } Argument name
16. fun main(args: Array<String>): Unit { println("Hello, World!") } Argument type
17. fun main(args: Array<String>): Unit { println("Hello, World!") } Return type
18. fun main(args: Array<String>): Unit { println("Hello, World!") }
19. fun main(args: Array<String>): Unit {. println("Hello, World!") }. Unit inferred
20. fun main(args: Array<String>) {. println("Hello, World!") }.
21. fun main(args: Array<String>) {. println("Hello, World!") }.
22. fun main(args: Array<String>) {. println("Hello, World!") }.
23. fun main(args: Array<String>) {. var name = "World" println("Hello, $name!") }.
24. fun main(args: Array<String>) {. var name = "World" println("Hello, $name!") }. Variable declaration
25. fun main(args: Array<String>) {. var name = "World" println("Hello, $name!") }. String interpolation
26. fun main(args: Array<String>) {. var name = "World" if (args.isNotEmpty()) { name = args[0] } println("Hello, $name!") }.
27. fun main(args: Array<String>) {. var name = "World" if (args.isNotEmpty()) { name = args[0] } println("Hello, $name!") }.
28. fun main(args: Array<String>) {. val name = "World" if (args.isNotEmpty()) { name = args[0] } println("Hello, $name!") }.
29. fun main(args: Array<String>) {. val name = "World" if (args.isNotEmpty()) { name = args[0] } println("Hello, $name!") }. Constant declaration
30. fun main(args: Array<String>) {. val name = "World" if (args.isNotEmpty()) { name = args[0] }. println("Hello, $name!") }. Val cannot be reassigned
31. fun main(args: Array<String>) {. val name = "World" if (args.isNotEmpty()) { name = args[0] }. println("Hello, $name!") }.
32. fun main(args: Array<String>) {. val name = if (args.isNotEmpty()) { args[0] } else { "World" }. println("Hello, $name!") }.
33. fun main(args: Array<String>) {. val name = if (args.isNotEmpty()) { args[0] } else { "World" }. println("Hello, $name!") }.
34. fun main(args: Array<String>) {. val name = if (args.isNotEmpty()) { args[0] } else { "World" }. println("Hello, $name!") }. Conditional assignment block
35. fun main(args: Array<String>) { val name = if (args.isNotEmpty()) { args[0] } else { "World" }. println("Hello, $name!") }.
36. fun main(args: Array<String>) { val name = if (args.isNotEmpty()) args[0] else "World" println("Hello, $name!") }.
37. class Person(var name: String) fun main(args: Array<String>) { val name = if (args.isNotEmpty()) args[0] else "World" println("Hello, $name!") }.
38. class Person(var name: String) fun main(args: Array<String>) { val name = if (args.isNotEmpty()) args[0] else "World" println("Hello, $name!") } Class keyword
39. class Person(var name: String) fun main(args: Array<String>) { val name = if (args.isNotEmpty()) args[0] else "World" println("Hello, $name!") } Class name
40. class Person(var name: String) fun main(args: Array<String>) { val name = if (args.isNotEmpty()) args[0] else "World" println("Hello, $name!") } Primary constructor
41. class Person(var name: String) fun main(args: Array<String>) { val name = if (args.isNotEmpty()) args[0] else "World" println("Hello, $name!") } Non-final class member
42. class Person(var name: String) fun main(args: Array<String>) { val name = if (args.isNotEmpty()) args[0] else "World" println("Hello, $name!") }
43. class Person(var name: String) fun main(args: Array<String>) { println("Hello, $name!") }
44. class Person(var name: String) fun main(args: Array<String>) { val person = Person("Roman") println("Hello, $name!") }
45. class Person(var name: String) fun main(args: Array<String>) { val person = Person(“Roman”) println("Hello, $name!") }. Instance declaration
46. class Person(var name: String) fun main(args: Array<String>) { val person = Person("Roman") println("Hello, $name!") }.
47. class Person(var name: String) fun main(args: Array<String>) { val person = Person("Roman") println("Hello, ${person.name}!") }. > Hello, Roman!
48. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") } class Person(var name: String) fun main(args: Array<String>) { val person = Person("Roman") println("Hello, ${person.name}!") }.
49. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }.. class Person(var name: String). fun main(args: Array<String>) { val person = Person("Roman") println("Hello, ${person.name}!") }.
50. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }.. class Person(var name: String, var lang: Language). fun main(args: Array<String>) { val person = Person("Roman") println("Hello, ${person.name}!") }.
51. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }.. class Person(var name: String, var lang: Language = Language.EN). fun main(args: Array<String>) { val person = Person("Roman") println("Hello, ${person.name}!") }. Default value
52. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) fun main(args: Array<String>) { val person = Person("Roman") println("Hello, ${person.name}!") }..
53. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }. fun main(args: Array<String>) { val person = Person("Roman") println("Hello, ${person.name}!") }..
54. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") } class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") } fun main(args: Array<String>) { val person = Person("Roman") println("Hello, ${person.name}!") }
55. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") } class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") } fun main(args: Array<String>) { val person = Person("Roman") }
56. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") } class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") } fun main(args: Array<String>) { val person = Person("Roman") person.greet() } > Hello, Roman!
57. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. fun main(args: Array<String>) { }.
58. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. fun main(args: Array<String>) { val people = listOf( Person("Roman"), Person("Romario", Language.SP), Person("Roman de Belov", Language.FR) ). }.
59. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. fun main(args: Array<String>) { val people = listOf( Person("Roman"), Person("Romario", Language.SP), Person("Roman de Belov", Language.FR) ). for (person in people) {. person.greet() }. }.
60. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. fun main(args: Array<String>) { val people = listOf( Person("Roman"), Person("Romario", Language.SP), Person("Roman de Belov", Language.FR) ). people.forEach {.person -> person.greet() }. }.
61. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. fun main(args: Array<String>) { val people = listOf( Person("Roman"), Person("Romario", Language.SP), Person("Roman de Belov", Language.FR) ). people.forEach { it.greet() }. }.
62. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. fun main(args: Array<String>) { listOf( Person("Roman"), Person("Romario", Language.SP), Person("Roman de Belov", Language.FR) ).forEach { it.greet() }. }. > Hello, Roman! > Hola, Romario! > Bonjour, Roman de Belov!
63. Null-safety
65. “Billion dollar mistake” — Sir C. A. R. Hoare
66. Java String s = null; s.length(); Errors At Runtime Kotlin val s: String s.length() val s: String? = null s.length() Errors At Compile Time = null Nullable type
67. Check and use val s: String? = … if (s != null) { s.length() } Check and exit if (s == null) return s.length() Rock’n’Roll s?.length() s!!.length() (s ?: “…”).length()
68. public class JavaClass { public String foo(List<String> l) {…} }
69. public class JavaClass { public String foo(List<String> l) {…} } String String? List<String> List<String?> List<String>? List<String?>? Safest! public class JavaClass { public String foo(List<String> l) {…} }
70. Java Interop: All Nullable javaValue.toString().length() + 1 javaValue?.toString()?.length()!! + 1 val l: List<String> = javaValue?.getList()!! ArrayList<String?>
71. Your safest option doesn’t work!
72. Annotations public class JavaClass { public String foo(List<String> l) {…} } String String? List<String> List<String?> List<String>? List<String?>? public class JavaClass { @NotNull public String foo(@NotNull List<String> l) {…} }
73. Annotations are cumbersome and don’t really help!
74. • Null-safety • Convenience • Java Interop Pick Two Platform Types! Thanks to Dr. Ross Tate of
75. String! List<String!>! public class JavaClass { public String foo(List<String> l) {…} } Java: Platform Types Platform Type
76. Dereferencing Platform Values s: String s: String? s: String! s.length() s.length() s.length() s?.length() s?.length() s?.length() s!!.length() s!!.length() s!!.length() NPE
77. Assignability String String? String! Platform Type Not Transitive! NPE
78. Some Notes • Platform Types are Not Denotable! – String! is notation, not syntax • Pure Kotlin is Null-Safe • Kotlin+Java is as safe as Java • Annotations Still Applicable – @NotNull String in Java becomes String in Kotlin • Dynamic Type for JavaScript Interop – JS is even unsafer than Java
79. Interoperability • Use all Java libraries 
 from Kotlin • Use Kotlin code from Java • Keep Java and Kotlin code
 side-by-side in project • Search/refactorings work
 cross-language
80. • Modern • Concise • Safe • Extensible • Interoperable • Fun to work with! Kotlin
81. Pragmatism
82. Resources • kotlinlang.org • discuss.kotlinlang.org • try.kotlinlang.org • slack.kotlinlang.org • kotlinconf.com
 (3-5 Oct. 2018, Amsterdam)
83. Спасибо за внимание —