Kotlinウォークスルー

第2回かわいいKotlin勉強会の発表資料です

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1. Kotlin ΢ΥʔΫεϧʔ 2014-07-04 ୈ2ճ͔Θ͍͍Kotlinษڧձ ! ೔ຊKotlinϢʔβάϧʔϓ
 ௕ᖒ ଠ࿠
2. Kotlinͱ͸ • ϓϩάϥϛϯάݴޠ • JVMͰಈ͘ • JetBrains͕த৺ʹ։ൃ͍ͯ͠ΔOSS • 2011೥ʹൃද • ݱόʔδϣϯ͸0.7
3. ͳͥ,PUMJOͳͷ͔ • δϟό͸ͪΐͬͱ… • Scalaͬͯػೳ͕ଟͯ͘೉͍͠ • Groovy͸ಈతͰ೉͍͠ • ͪΐ͏Ͳ͍͍ͱ͜Ζ͕ཉ͍͠ʂ
4. Kotlin͕໨ࢦ͢ͱ͜Ζ • γϯϓϧ • ҆શ • εϐʔυ ͬ͘͟Γݴ͏ͱ…
5. Kotlinͷಛ௃ • ؆ܿ • ҆શ • JVMͰಈ͘ • JavaScriptʹ΋ม׵Ͱ͖Δ • ੩తܕ෇͚ • ΦϒδΣΫτࢦ޲ • ؔ਺ܕϓϩάϥϛϯά
6. Hello World package hello fun main(args : Array<String>) { println("Hello, world!") }
7. Hello World package hello fun main(args : Array<String>) { println("Hello, world!") } ύοέʔδ௚Լʹ ؔ਺͕ஔ͚Δ ΤϯτϦϙΠϯτ͸ mainؔ਺
8. Hello World package hello fun main(args : Array<String>) { println("Hello, world!") } ม਺ͷܕ͕ޙஔ ഑ྻ͕ δΣωϦΫε
9. Hello World package hello fun main(args : Array<String>) { println("Hello, world!") } ηϛίϩϯ ෆཁ
10. Ϋϥε class Greeter ! val greeter = Greeter()
11. Ϋϥε class Greeter ! val greeter = Greeter() ࠷খͷ Ϋϥεఆٛ
12. Ϋϥε class Greeter ! val greeter = Greeter() ΠϯελϯεԽ newෆཁ ܕࢦఆෆཁ: ܕਪ࿦
13. Ϋϥε class Greeter(val name: String) { fun greet() { println("Hello, $name") } }
14. Ϋϥε class Greeter(val name: String) { fun greet() { println("Hello, $name") } } ϓϩύςΟ val g = Greeter(“hoge”) val name = g.name
15. Ϋϥε class Greeter(val name: String) { fun greet() { println("Hello, $name") } } ϝιου ࣜ(ม਺)ΛຒΊࠐΊΔ
16. ϓϩύςΟ class User(name: String) { var name: String = name } ! val user = User("Taro") user.name / / => "Taro"
17. ϓϩύςΟ class User(name: String) { var name: String = name } ! val user = User("Taro") user.name / / => "Taro" ίϯετϥΫλ ϓϩύςΟ
18. ϓϩύςΟ class User(name: String) { var name: String = name } ! val user = User("Taro") user.name / / => "Taro" ϑΟʔϧυʹ௚઀ ΞΫηεͯ͠Δ෩
19. ΞΫηα class User(name: String) { var name: String = name set(name: String) {$name = name } get(): String = $name }
20. ΞΫηα class User(name: String) { var name: String = name set(name: String) {$name = name } get(): String = $name } Setter Getter Backing Field
21. Delegated Property class User(name: String) { val name: String by Decorator(name) } ! class Decorator(val str: String) { fun get(thisRef: Any, prop:PropertyMetadata): String = "<<$str>>" }
22. Delegated Property class User(name: String) { val name: String by Decorator(name) } ! class Decorator(val str: String) { fun get(thisRef: Any, prop:PropertyMetadata): String = "<<$str>>" } User#name΁ͷ ΞΫηε͕ҕৡ͞ΕΔ
23. Ԡ༻ྫ class MainActivity: Activity() { val submitButton: Button by injector() ! fun onCreate(savedInstanceState: Bundle?) { submitButton.setOnClickListener(::submit) } }
24. ܕ҆શ val a: Array<Int> = array(1, 2, 3) val b: Array<Number> = a / / NG val c: Array<out Number> = a / / OK ! a[0] = 5 / / OK c[0] = 5 / / NG
25. ܕ҆શ val a: Array<Int> = array(1, 2, 3) val b: Array<Number> = a / / NG val c: Array<out Number> = a / / OK ! a[0] = 5 / / OK c[0] = 5 / / NG Array͸σϑΥϧτͰ ෆม(invariant) มҐࢦఆ͕Մೳ ͜͜Ͱ͸ڞม(covariant)
26. ܕ҆શ val a: Array<Int> = array(1, 2, 3) val b: Array<Number> = a / / Error val c: Array<out Number> = a / / OK ! a[0] = 5 / / OK c[0] = 5 / / NG ܕͷෆ੔߹Λ ๷͍Ͱ͘ΕΔ
27. એݴՕॴ෼ࢄ val a: List<Int> = listOf(1, 2, 3) val b: List<Number> = a / / OK ———————————————————————— class List<out T> …
28. એݴՕॴ෼ࢄ val a: List<Int> = listOf(1, 2, 3) val b: List<Number> = a ———————————————————————— class List<out T> … Ϋϥεͷએݴ࣌ʹ มҐࢦఆͰ͖Δ
29. ؔ਺͕first-class val add = { (a: Int, b: Int) -> a + b } ! add(3, 4) / / => 7
30. ؔ਺͕first-class list.filter({ (e: Int) -> e % 2 != 0 })
31. ؔ਺͕first-class list filter { it % 2 != 0 }
32. Single Abstract Method / / Java static void invoke(Runnable r) { r.run(); } ! / / Kotlin Sample.invoke { hoge() } Runnableͷ୅ΘΓʹ ()->Unitͳؔ਺Λࢦఆ
33. ΠϯϥΠϯؔ਺ inline fun invoke(f: ()->Unit) { f() }
34. ΠϯϥΠϯؔ਺ inline fun invoke(f: ()->Unit) { f() } inlineΞϊςʔγϣϯ: ΠϯϥΠϯల։͞ΕΔ ؔ਺ͷܕ (Ҿ਺ͷܕ)->ฦ஋ͷܕ
35. ֦ுؔ਺ fun String.hello() { println("Hello, $this") } ! "World".hello()
36. ֦ுؔ਺ + ؔ਺ΦϒδΣΫτ fun String.hello() { println("Hello, $this") } ! "World".hello()
37. TCO tailRecursive fun sum(ints: List<Int>, sum: Int = 0): Int = if(ints.isEmpty()) sum else sum(ints.tail, sum + ints.first())
38. TCO tailRecursive fun sum(ints: List<Int>, sum: Int = 0): Int = if(ints.isEmpty()) sum else sum(ints.tail, sum + ints.first()) tailRecursive Ξϊςʔγϣϯ
39. null҆શ val a: Int = null / / OK val b: Int? = null / / NG b.toString() / / NG if(b != null) b.toString() / / OK b?.toString() / / OK
40. null҆શ val a: Int = null / / OK val b: Int? = null / / NG b.toString() / / NG if(b != null) b.toString() / / OK b?.toString() / / OK if (b != null) b.toString() else null
41. null҆શ fun toInt(s: String): Int? fun square(n: Int): Int จࣈྻΛtoInt()Ͱ਺஋ʹม׵ ͦͷ਺Λsquare()Ͱೋ৐͍ͨ͠
42. ෳࡶ… if(s != null) { val i = toInt(s) if(i != null) square(i) else null } else { null }
43. ศརͳؔ਺Λಋೖ fun <T, R> T.bind(f: ((T) -> R)?): R = f?.invoke(this)
44. bindΛ࢖͏ͱΩϨΠʹͳΔ s?.bind(::toInt)?.bind(::square)
45. ͝ਗ਼ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠