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Swift flatMap
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USAMI Kosuke
February 28, 2017
Programming
4
990
Swift flatMap
https://kanmoba.connpass.com/event/51628/
USAMI Kosuke
February 28, 2017
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Transcript
flatMap ͷ USAMI Kosuke Fenrir Inc.
͡Ίʹ • Swi% ͷ flatMap ʹ͍ͭͯ͠·͢ • flatMap ͦͷͷ͍Ζ͍Ζͳݴޠʹ͋Γ·͢
flatMap • Α͘Θ͔Βͳ͍Πϝʔδ͕͋Δʁ • ίʔυ͕ಡΈͮΒ͍ʁ • map ͯ͠ fla'en ͢Δͭʁ
• ؔܕʁ Ϟφυʁ
flatMap • ݸਓతʹɺؾָʹ͍͍͑ͱࢥ͏
Op#onal ͷ flatMap
Op#onal ͷ flatMap • มલ : Optional<T> • มॲཧ :
T -> Optional<U> • flatMap : Optional<T> -> Optional<U> • มલ͕ non-nil ͳΒมॲཧΛద༻͢Δ • มલ͕ nil ͳΒมॲཧΛద༻͠ͳ͍
ྫ • มલ : Optional<String> • มॲཧ : String ->
Optional<Int> : { Int($0) } • string.flatMap { Int($0) } • "123" -> Int("123") -> 123 • "abc" -> Int("abc") -> nil • nil -> nil
nil ͷೖྗΛҙࣝ͠ͳ͍͍ͯ͘ // string Optional ͚ͩͲɾɾɾ let string: String?
= "123" let integer: Int? = string.flatMap { Int($0) // $0 unwrap ͞Ε͍ͯΔ }
if let Ͱॻ͘ͱʹͳΔ let string: String? = "123" let integer:
Int? if let string = string { integer = Int(string) } else { integer = nil }
Op#onal chaining ෩ʹ͏ // Optional chaining string?.isEmpty // ಉ༷ʹ͜Μͳͷ͕ཉ͘͠ͳΔʁ string?.toInt
// ΘΓʹ͜͏͢Δ string.flatMap { Int($0) }
Array ͷ flatMap
Array ͷ flatMap • 2 छྨͷ flatMap ͕ଘࡏ͢Δ
Array ͷ flatMap (1) • มલ : Array<T> • มॲཧ
: T -> Array<U> • flatMap : Array<T> -> Array<U>
ྫ • มલ : Array<Int> • มॲཧ : Int ->
Array<Int> : { [$0, $0 * 10] } • [1, 2, 3].flatMap { [$0, $0 * 10] } • 1 -> [1, 10], 2 -> [2, 20], 3 -> [3, 30] • [1, 10, 2, 20, 3, 30]
Op#onal ͱ Array ͷ flatMap ൺֱ • มલ : Optional<T>
• มॲཧ : T -> Optional<U> • flatMap : Optional<T> -> Optional<U> • มલ : Array<T> • มॲཧ : T -> Array<U> • flatMap : Array<T> -> Array<U>
flatMap ͷجຊܗ • ܕ T U ͕ೖͬͨԿΒ͔ͷശʢBoxʣ͕͋Δͱ͖ʹ • มલ
: Box<T> • มॲཧ : T -> Box<U> • flatMap : Box<T> -> Box<U>
Array ͷ flatMap (2) • มલ : Array<T> • มॲཧ
: T -> Optional<U> • flatMap : Array<T> -> Array<U> • มॲཧͷ݁Ռ͕ non-nil ͷͷ͕ Array ͷཁૉʹͳΔ • มॲཧͷ݁Ռ͕ nil ͷͷࣺͯΒΕΔ
ྫ • มલ : Array<String> • มॲཧ : String ->
Optional<Int> : { Int($0) } • ["123", "abc"].flatMap { Int($0) } • "123" -> 123, "abc" -> nil • [123]
Array ͷ 2 ͭͷ flatMap ͷؔ • flatMap (2)
flatMap (1) Ͱ࣮ݱͰ͖Δ • non-nil Λฦ͢ΘΓʹ1ཁૉͷ Array Λฦ͢ • nil Λฦ͢ΘΓʹۭͷ Array Λฦ͢ • flatMap (2) ͷํ͕ίʔυ͕γϯϓϧʹͳΔ • flatMap (1) ࣮͋Μ·ΓΘͳ͍
׆༻ྫ • ["A", "B", nil, "C"] : [String?] • ͔͜͜Β
nil ΛऔΓআ͍ͨ [String] ͕ཉ͍͠ // flatMap ͳ͠ͳΒɺ͜Μͳײ͡Ͱॻ͘ʁ ["A", "B", nil, "C"] .filter({ $0 != nil }) as! [String]
׆༻ྫ // ୯ʹ͜͏ॻ͚ྑ͍ ["A", "B", nil, "C"].flatMap { $0 }
• มલ : Array<Optional<String>> • มॲཧ : Optional<String> -> Optional<String> • flatMap : Array<Optional<String>> -> Array<String>
flatMap Λ׆༻͢Δ໘ • Op$onal ͱͷ૬ੑ͕ྑ͍ • Op$onal Λѻ͏ॲཧ͕͋Δͱ͖ʹ͑ͳ͍͔ߟ͑Δͱྑ͍
ࢀߟɿଞʹ flatMap ͕͑Δͷ • Result ܕʢan+typical/Resultʣ • Op+onal ͱ΄΅ಉ͡ʢnil ͷΘΓʹ۩ମతͳ
Error Λฦ͢ʣ • Observable ܕʢRxSwi:ʣ • ඇಉظετϦʔϜɺ్தͰΤϥʔʹͳͬͨ߹ͷରԠ͕༰қ
flatMap Λ্खʹ׆༻͠Α͏