Kotlinらしいコード #jkug

第3回かわいいKotlin勉強会
https://kotlin.doorkeeper.jp/events/23515

Transcript

1. KotlinΒ͍͠ίʔυ 
   ୈճ
   ͔Θ͍͍,PUMJOษڧձ
   ! ೔ຊ,PUMJOϢʔβάϧʔϓ
 ௕ᖒ
   ଠ࿠
   !OHTX@UBSP
2. ࣗݾ঺հ w ௕ᖒ
   ଠ࿠
   !OHTX@UBSP
   w ࢓ࣄͰ͸+BWB
   4DBMB
   "OESPJE
   w ࣗশ,PUMJOΤϰΝϯδΣϦετ
   w ࡀɺֈ࠲ɺͱ͕େ޷͖
3. Έͳ͞Μ KotlinΒ͍͠ίʔυ ॻ͍ͯ·͔͢ʁ
4. w +BWBܦݧ͋Γˠ,PUMJO؆୯
   ! w ؔ਺Ϧςϥϧɺߴ֊ؔ਺
   w ֦ுؔ਺ɺ%FMFHBUFE
   1SPQFSUZ
   w /6--҆શ KotlinͬΆ͍ίʔυʁ ػೳଟͯ͘
   ࢖͍͜ͳͤΜ ͱ͸ݴͬͯ΋ʜ
5. ຊ೔ͷςʔϚ KotlinΒ͍͠ίʔυ KotlinͷػೳΛ׆͔ͨ͠ίʔυ
6. ୊ࡐ1. sum
7. fun sum(xs: List<Int>): Int {! var sum = 0! for(x in ints) {! sum += x! }! return sum! }
8. fun sum(xs: List<Int>): Int {! var sum = 0! for(x in ints) {! sum += x! }! return sum! } WBSݏͩͳʔ
9. fun sum(xs: List<Int>): Int {! @tailRecursive! fun go(xs: List<Int>, a: Int): Int {! if(xs.isEmpty())! return a! else! return go(xs.drop(1), a + xs.first())! }! ! return go(xs, 0)! }
10. fun sum(xs: List<Int>): Int {! @tailRecursive! fun go(xs: List<Int>, a: Int): Int {! if(xs.isEmpty())! return a! else! return go(xs.drop(1), a + xs.first())! }! ! return go(xs, 0)! } ຤ඌݺͼग़͠࠷దԽΛ༗ޮ
11. fun sum(xs: List<Int>): Int {! @tailRecursive! fun go(xs: List<Int>, a: Int): Int {! if(xs.isEmpty())! return a! else! return go(xs.drop(1), a + xs.first())! }! ! return go(xs, 0)! } ϩʔΧϧؔ਺
12. fun sum(xs: List<Int>): Int {! @tailRecursive! fun go(xs: List<Int>, a: Int): Int {! if(xs.isEmpty())! return a! else! return go(xs.drop(1), a + xs.first())! }! ! return go(xs, 0)! } JGͰ΋FMTFͰ΋SFUVSO
    ؾ࣋ͪѱ͍ʜ JGͰ΋FMTFͰ΋SFUVSO
    ؾ࣋ͪѱ͍ʜ
13. fun sum(xs: List<Int>): Int {! @tailRecursive! fun go(xs: List<Int>, a: Int): Int {! return if(xs.isEmpty()) a! else go(xs.drop(1), a + xs.first())! }! ! return go(xs, 0)! }
14. fun sum(xs: List<Int>): Int {! @tailRecursive! fun go(xs: List<Int>, a: Int): Int {! return if(xs.isEmpty()) a! else go(xs.drop(1), a + xs.first())! }! ! return go(xs, 0)! } JGFMTF͸ࣜ
15. fun sum(xs: List<Int>): Int {! @tailRecursive! fun go(xs: List<Int>, a: Int): Int {! return if(xs.isEmpty()) a! else go(xs.drop(1), a + xs.first())! }! ! return go(xs, 0)! } ΋ͬͱ
    ͔ͬ͜Α͘Ͱ͖Δ
16. fun sum(xs: List<Int>): Int {! @tailRecursive! fun go(xs: List<Int>, a: Int): Int =! if(xs.isEmpty()) a! else go(xs.drop(1), a + xs.first())! ! return go(xs, 0)! }
17. fun sum(xs: List<Int>): Int {! @tailRecursive! fun go(xs: List<Int>, a: Int): Int =! if(xs.isEmpty()) a! else go(xs.drop(1), a + xs.first())! ! return go(xs, 0)! } ୯Ұࣜؔ਺
18. fun sum(xs: List<Int>): Int =! xs.fold(0) { a, x -> a + x }
19. fun sum(xs: List<Int>): Int =! xs.fold(0) { a, x -> a + x } ඪ४"1*
    ࠨ৞ΈࠐΈ
20. fun sum(xs: List<Int>): Int =! xs.fold(0) { a, x -> a + x } ؔ਺Ϧςϥϧ
21. fun List<Int>.sum(): Int =! fold(0) { a, x -> a + x }
22. fun List<Int>.sum(): Int =! fold(0) { a, x -> a + x } ֦ுؔ਺
24. (sumͳΜ͔ࣗ࡞͠ͳ͍)
25. ! ! ඪ४API fun Iterable<Int>.sum(): Int (sumͳΜ͔ࣗ࡞͠ͳ͍)
26. ୊ࡐ1. sum ·ͱΊ w WBSݏͩ
    w UBJM3FDVSTJWFͰ5$0
    w ϩʔΧϧؔ਺
    w JGFMTF͸ࣜ
    w GVO
    IPHF
    
    
    Ͱ୯Ұࣜؔ਺
    w ֦ுؔ਺
    w ඪ४"1*Λ࢖͏
27. ୊ࡐ2. nullable
28. // ໊લΛऔಘͰ͖Δ! fun getName(): String?! ! // อଘͰ͖Δ! fun save(s: String): Unit
29. val name: String? = getName()! if(name != null) {! save(name)! }
30. val name: String? = getName()! if(name != null) {! save(name)! } OVMMνΣοΫ ͜ͷதͰOBNF͸
    OPU/VMMͱͯ͠ѻ͑Δ
31. name?.let {! name -> save(name)! }
32. name?.let {! name -> save(name)! } ඪ४"1*
    MFUؔ਺
33. name?.let {! name -> save(name)! } ඪ४"1*
    MFUؔ਺ ҆શݺͼग़͠
34. name?.let {! save(it)! }
35. name?.let {! save(it)! } ҉໧ͷม਺
    JU
36. name?.let(::save)
37. name?.let(::save) ؔ਺ࢀর
38. ୊ࡐ2. nullable ·ͱΊ w OVMMνΣοΫ͍͢͝
    w 
    ͷ҆શݺͼग़͠ศར
    w MFUؔ਺໘ന͍
    w ҉໧ͷม਺
    JU
    w ؔ਺ࢀর
    w ͓·͚
    IUUQTTQFBLFSEFDLDPNOUBSP LPUMJOOVNCFSTIJCVJHVKWN
39. ୊ࡐ3. immutable
40. class User(id: Long, name: String) {! val id = id! val name = name! ! class Builder {! var id: Long? = null! var name: String? = null! ! fun id(id: Long): Builder {! this.id = id! return this! }! ! fun name(name: String): Builder {! this.name = name! return this! }! ! fun build(): User {! val id = checkNotNull(id)! val name = checkNotNull(name)! return User(id, name)! }!
41. val taro = User.Builder()! .id(123)! .name(“Taro”)! ! .build()! ! val jiro = taro.builder()! .name(“Jiro”)! .build() qVFOU
    JOUFSGBDFͰ
    JNNVUBCMFͳ΍ͭ
42. data class User(! val id: Long,! val name: String! )
43. data class User(! val id: Long,! val name: String! ) EBUBΞϊςʔγϣϯ ϓϩύςΟ
44. val taro = User(id=123, name=“Taro”)! ! val jiro = taro.copy(name=“Jiro”)
45. val taro = User(id=123, name=“Taro”)! ! val jiro = taro.copy(name=“Jiro”) ໊લ෇͖Ҿ਺
46. val taro = User(id=123, name=“Taro”)! ! val jiro = taro.copy(name=“Jiro”) EBUBΞϊςʔγϣϯʹΑΔ
    DPQZϝιου
47. ୊ࡐ3. immutable ·ͱΊ w EBUBΞϊςʔγϣϯڧ͍
    w ໊લ෇͖Ҿ਺
    w ˢ΋͏-PNCPLܥ#VJMEFSύλʔϯཁΒͳ͍
48. ୊ࡐ4. decorator
49. class GreetableCharSeq! (private val cs: CharSequence): CharSequence {! ! fun hello() {! println("Hello, ${cs}")! }! ! override fun length(): Int = cs.length()! override fun charAt(index: Int): Char = cs.charAt(index)! override fun subSequence(start: Int, end: Int): CharSequence =! cs.subSequence(start, end)! }
50. class GreetableCharSeq! (private val cs: CharSequence): CharSequence {! ! fun hello() {! println("Hello, ${cs}")! }! ! override fun length(): Int = cs.length()! override fun charAt(index: Int): Char = cs.charAt(index)! override fun subSequence(start: Int, end: Int): CharSequence =! cs.subSequence(start, end)! } $IBS4FRVFODFʹ
    IFMMPϝιουͷ௥Ճ͕͍ͨ͠
51. class GreetableCharSeq! (private val cs: CharSequence): CharSequence {! ! fun hello() {! println("Hello, ${cs}")! }! ! override fun length(): Int = cs.length()! override fun charAt(index: Int): Char = cs.charAt(index)! override fun subSequence(start: Int, end: Int): CharSequence =! cs.subSequence(start, end)! } ͦͷଞͷϝιου͸
    ͦͷ··ϥοϓͯ͠Δ࣮૷ʹ
    ҕৡ
52. class GreetableCharSeq! (private val cs: CharSequence): CharSequence by cs {! fun hello() {! println("Hello, ${cs}")! }! }
53. class GreetableCharSeq! (private val cs: CharSequence): CharSequence by cs {! fun hello() {! println("Hello, ${cs}")! }! } CZͰҕৡ ҕৡ͢Δ͚ͩͷ
    ϝιου͸هड़ෆཁ
54. ࣮ࡍ͸… fun CharSequence.hello() {! println(“Hello, $this”)! }
55. ୊ࡐ4. decorator ·ͱΊ w EFDPSBUPSύλʔϯΈ͍ͨͳͷ͍ͨ͠ͱ͖͸ CZΩʔϫʔυʹΑΔҕৡͷ࢓૊ΈΛ࢖͏
    w ࠓճͷྫͰ͸֦ுؔ਺ͰࡁΜͩ
56. ͝ਗ਼ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠