SwiftのmapとflatMapを雑に解説する / map and flatMap on Swift

tokushima.app で発表 **しなかった** スライドです。

2015年の年末あたりに、次のtokushima.appで発表しようと考えて作ったのですが、会場の都合でしばらく開かれなくて完全にタイミングを逃し、次に開かれたときには別のことを発表しました😓

Transcript

1. 4XJGUͷNBQͱqBU.BQΛ
   ࡶʹղઆ͢Δ !IJSPOZUJD
   ʢҰٶߒڭʣ
   UPLVTIJNBBQQ
   
2. "SSBZͷNBQ let array: [Int] = [1, 3, 8] array.map {x in x + 1}
3. ͪΐͬͱ୤ઢ array.map {x in x + 1} array.map({ (x: Int) -> Int in return x + 1 })
4. "SSBZͷNBQ let array: [Int] = [1, 3, 8] array.map {x in x + 1}
5. "SSBZͷNBQ let array: [Int] = [1, 3, 8] array.map {x in x + 1}    f(x) f(x) f(x) f(x) = x + 1   
6. "SSBZͷNBQ let array: [Int] = [1, 3, 8] array.map {x in [x, x + 1]}
7. "SSBZͷNBQ let array: [Int] = [1, 3, 8] array.map {x in [x, x + 1]}    f(x) f(x) f(x) f(x) = [x, x + 1]      
8. "SSBZͷqBU.BQ let array: [Int] = [1, 3, 8] array.flatMap {x in [x, x + 1]}    f(x) f(x) f(x) f(x) = [x, x + 1]      
9. 0QUJPOBMͷNBQ let value: Int? = … value.map {x in x + 1}
10. ·ͨ·ͨ୤ઢ [Int] Array<Int> Int? Optional<Int>
11. 0QUJPOBMͷNBQ let value: Int? = … value.map {x in x + 1}
12. 0QUJPOBMͷNBQ let value: Int? = … value.map {x in x + 1} let value: Int? = 16 value.map {x in x + 1}  f(x)  let value: Int? = nil value.map {x in x + 1} OJM OJM
13. ΞΠςϜ਺
    σʔλ͕ͳ͍
    ΞΠςϜ਺
    σʔλ͕͋Δ
    "SSBZ
    
    
    
    
    
    <
    
    >
    
    
    
    
    
    
    
    
    <> 0QUJPOBM
    
    
    
    
    
    
    
    
    
    OJM
    /POF
    
    
    
    
    
    
    
    
    
    
    4PNF  "SSBZͱ0QUJPOBM  OJM 
14. NBQ let array: [Int] = [] array.map {x in x + 1} -> [] let array: [Int] = [16] array.map {x in x + 1} -> [17] let value: Int? = nil value.map {x in x + 1} -> nil let value: Int? = 16 …Int?(16) value.map {x in x + 1} -> 17 …Int?(17)
15. qBU.BQ let array: [Int] = [] array.flatMap {x in [x + 1]} -> [] let array: [Int] = [16] array.flatMap {x in [x + 1]} -> [17] let value: Int? = nil value.flatMap {x in Int?(x + 1)} -> nil let value: Int? = 16 …Int?(16) value.flatMap {x in Int?(x + 1)} -> 17 …Int?(17)
16. 0QUJPOBMͷqBU.BQ let value: Int? = … value.flatMap {x -> Int? in if (x < 1) { return nil // ܭࢉࣦഊ } else { return x - 1 } }
17. ·ͱΊ func plusOne(x: Int) -> Int { return x + 1 } let array: [Int] = [1, 3, 8] array.map(plusOne) let value: Int? = 16 value.map(plusOne) w NBQ͸ശ͔Βग़ͯ͠ɺؔ਺Λద༻ ͯ͠ശʹೖΕΔɻ
    w qBU.BQ͸ശ͔Βग़ͯ͠ɺؔ਺Λ ద༻ͯ͠ϑϥοτʹശʹೖΕΔɻ
    w NBQ
    qBU.BQΛ࢖͏ͱɺͦ͜ʹ ౉͞ΕΔؔ਺͸֎ଆͷੈքΛҙࣝ ͠ͳ͍͍ͯ͘ʂ
18. ࢀߟαΠτ w 4XJGUͷ0QUJPOBMܕΛۃΊΔ
 IUUQRJJUBDPNLPIFSJUFNTDGCBEBCG
    w Ϟφυʹ͍ͭͯ4XJGUͰઆ໌ͯ͠Έͨ
 IUUQRJJUBDPNLPIFSJUFNTGGGDECGBDG
    w +BWBͷ0QUJPOBMͷϞφυతͳ࢖͍ํ
 IUUQRJJUBDPNLPIFSJUFNTGBECBECG