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DI with "Reader Monad"
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to4iki
March 26, 2018
1
1.3k
DI with "Reader Monad"
iOS Test Night #7
2018/03/26
https://github.com/to4iki/Reader
to4iki
March 26, 2018
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Transcript
DI with Reader Monad iOS Test Night #7 2018/03/26 @to4iki
1
Me • Takezawa Toshiki • @to4iki • iOS Engineer •
! ☕ ♨ 2
what DI? 3
֎෦͔Βґଘ(ΦϒδΣΫτ) ΛೖͰ͖ΔΑ͏ʹ͢Δ σβΠϯύλʔϯ 4
! ϝϦοτ • ίϯϙʔωϯτಉ͕࢜ૄ݁߹ʹͳΔ • I/FΛࢀর͢Δ͜ͱʹͳΔ • ΦϒδΣΫτͷੜͱ༻͕͞ΕΔ • ಈ࡞ΛॊೈʹΧελϚΠζͰ͖Δ
• ґଘ͢ΔΦϒδΣΫτΛࠩ͠ସ͑Δ͜ͱ͕Ͱ͖Δ • -> ςετ͕ॻ͚Δ ! 5
ಈతDI • DI Container ੩తDI • Initializer(Constructor) Injection • Property(Setter)
Injection • Cake Pattern • Reader Monad 6
Reader Monad 7
ؔϞφυ (Input) -> Element ͷϥούʔ struct Reader<Input, Element> { typealias
WorkFactory = (Input) -> Element private let workFactory: WorkFactory func execute(_ input: Input) -> Element { return workFactory(input) } } 8
map / flatMap func map<T>(_ f: @escaping (Element) -> T)
-> Reader<Input, T> { return Reader<Input, T> { input in f(self.execute(input)) } } func flatMap<T>(_ f: @escaping (Element) -> Reader<Input, T>) -> Reader<Input, T> { return Reader<Input, T> { input in f(self.execute(input)).execute(input) } } 9
ఆٛ͜Μ͚ͩ 10
ex. let plusTwoReader = Reader<Int, Int> { $0 + 2
} let xxxReader = plusTwoReader .map { $0 * 2 } .map { "value is \($0)" } xxxReader.execute(1) // "value is 6" xxxReader.execute(2) // "value is 8" plusTwoReader .flatMap { x in Reader<Int, Int> { y in x * y } } .execute(3) // 18 11
ධՁ͢Δ·Ͱɺ Πϯϓοτ(ґଘ)Λ Ԇͤ͞Δ͜ͱ͕Ͱ͖Δ 12
Example DI 13
ex. ! protocol UserServiceType { func find(by id: User.Id) ->
User? } struct UserService: UserServiceType { func find(by id: User.Id) -> User? { ... } } 14
ex. ! Dependency protocol Module { var userService: UserServiceType {
get } var tweetService: TweetServiceType { get } } 15
ex. ! Client func getTweets(by userId: User.Id) -> Reader<Module, [Tweet]>
{ return Reader { module in module.userService.find(by: userId) .map { $0.name } .map { module.tweetService.findAll(by: $0) } ?? [] } } 16
ex. ! Injection struct ProductionModule: Module { var userService: UserServiceType
{ return UserService.shared } var tweetService: TweetServiceType { return TweetService.shared } } getTweets("prod").execute(ProductionModule()) // [ATweet, BTweet, ...] getTweets("test").execute(MockModule()) // [TestTweet] 17
DI with Reader Monad Pros • ΦϒδΣΫτ୯ҐͰͳ͘ɺؔ୯Ґͷࡉ͔ͳDI͕ग़དྷΔ Cons • ReaderܕʹϩοΫΠϯ͞ΕΔ
• ͍͠ • ґଘ͕ෳʹͳΔͱѻ͍ʹ͍͘ • Ϟφυ͕ωετͨ࣌͠ͷѻ͍͕ʹͳΔ 18
Conclusion • DIख๏ͷҰͭʹReader MonadΛ༻ͨ͠ํ๏ ͕͋Δ • SwiftͰѻ͏ʹ࣮༻ݫ͍͠ҹ • functional-programmingΛಥ͖ਐΊΔڧ ͍ҙࢤͱ֮ޛ͕͋Ε...
• ༷ʑͳDIख๏͕͋Δ͕ɺίϯςΩετ (ϝϯόɾจԽ)ʹԠͨ͡ͷΛબ͠·͠ΐ͏ʂ 19
https://github.com/ to4iki/Reader 20
Thanks 21