Kotlin Nullable型をモナドっぽくしてみた

拡張関数を用いてNullable型を扱いやすくしてみました。

Transcript

1. Kotlin
 NullableܕΛϞφυͬΆͯ͘͠Έͨ 2014-04-05 ୈޒ.ޒճ #ौ୩java 
 ௕ᖒ ଠ࿠ @ngsw_taro
2. ॕʂJava8
3. Optional • ʮܭࢉͷࣦഊʯ΍ʮ஋ͷෆࡏʯͷՄೳੑΛදݱ͢Δ • nullͷ୅ΘΓ • (্ख͘࢖͑͹) ͵ΔΆΒͳ͍
4. Optional static Optional<Integer> toInt(String str) {! ! // Integerʹม׵ͯ͠ฦ͢! }! ————————————————————————————————————————————————! Optional<String> a = getA();! Optional<Integer> b = ! a.flatMap(Sample::toInt);
5. NPEͷढറ͔Β͸ಀΕΒΕͳ͍ Optional<String> str = null;
6. KotlinͷΞϓϩʔν (ࢿྉ) KotlinͷNull-Safetyػߏʹ͍ͭͯ https://speakerdeck.com/ntaro/kotlin-null-safetyji-gou-nituite
7. Nullableܕ≠Ϟφυ • Nullableܕม਺͸nullΛ୅ೖՄೳͳ͚ͩ • ࢖͑Δϝιου͕૿͑ΔΘ͚Ͱ͸ͳ͍ • NullableܕͷNullableܕͱ͔ೖΕࢠ͸Ͱ͖ͳ͍
8. nullνΣοΫͯ͠৔߹෼͚ fun toInt(str: String): Int? = ...! ——————————————————————————————————————————————! val a: String? = getA()! val b: Int? = if(a != null) toInt(a) else null
9. NullableܕΛϞφυͬΆͯ͘͠Έͨ
10. ͜ΕͰ0, fun <T,R> T.bind(f:(T)->R):R = f(this)
11. NotNull→Nullableͷؔ਺Λద༻Մ fun divide(a: Int, b: Int): Int?! ! ! ! ! ! ! = if(b == 0) null else (a / b)! val partial = (::divide).curried()(100)! ! 2.nullable()?.bind(partial) // => 50! 0.nullable()?.bind(partial) // => null! null?.bind(partial) // => null
12. NotNull→NotNullͷؔ਺Λద༻Մ fun square(i: Int): Int = i * i! ! 4.nullable()?.bind(::square) // => 16! null?.bind(::square) // => null
13. if-else ΛഉআͰ͖ͨʂ // before! val b: Int? = if(a != null) toInt(a) else null! ! // after! val b: Int? = a?.bind(::toInt)
14. Nullableͳؔ਺͸μϝ fun next(i: Int) = i + 1! val nullableNext = ::next.nullable()! ! val a: Int? = 5! nullableNext?.invoke(a) // ܕ͕߹Θͳ͍! a?.bind(nullableNext) // ܕ͕߹Θͳ͍
15. վྑ fun <T, R> T.bind(f: ((T) -> R)?): R?! = f?.invoke(this)
16. Nullableͳؔ਺΋ద༻Մ fun next(i: Int) = i + 1! val nullableNext = ::next.nullable()! ! val a: Int? = 5! a?.bind(nullableNext) // => 6! a?.bind(null) // => null
17. Applicative Functor fun minus(a: Int, b: Int) = a – b! val minus = ::minus.curried()! ! val a: Int? = 5! val b: Int? = 3! b?.bind(a?.bind(minus)) // => 2
18. ͜Μͳؔ਺Λಋೖͯ͠ΈΔ fun <T, R>! Function1<T, R>.apply(nullable: T?): R?! ! ! = nullable?.bind(this)
19. ΑΓ3FBEBCMFͳελΠϧ // before! b?.bind(a?.bind(minus))! ! // after! minus.apply(a)?.apply(b)
20. ੒Ռ Ҿ਺͕NotNullͷؔ਺ʹNullableΛ ৯ΘͤΒΕΔΑ͏ʹͳͬͨ ! ! ʮNullνΣοΫͯ͠෼ذʯΛഉআ͠ɺ ಡΈ΍͍͢ίʔυ͕ॻ͚Δ
21. NullableɺͦΜͳʹ໘౗͡Όͳ͍ʂ
22. curried() FunKTionale https://github.com/MarioAriasC/funKTionale
23. ͝ਗ਼ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠