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DI with Reader Monad
iOS Test Night #7
2018/03/26
@to4iki
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Me
• Takezawa Toshiki
• @to4iki
• iOS Engineer
•
! ☕ ♨
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what DI?
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֎෦͔Βґଘ(ΦϒδΣΫτ)
ΛೖͰ͖ΔΑ͏ʹ͢Δ
σβΠϯύλʔϯ
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!
ϝϦοτ
• ίϯϙʔωϯτಉ͕࢜ૄ݁߹ʹͳΔ
• I/FΛࢀর͢Δ͜ͱʹͳΔ
• ΦϒδΣΫτͷੜͱ༻͕͞ΕΔ
• ಈ࡞ΛॊೈʹΧελϚΠζͰ͖Δ
• ґଘ͢ΔΦϒδΣΫτΛࠩ͠ସ͑Δ͜ͱ͕Ͱ͖Δ
• -> ςετ͕ॻ͚Δ
!
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ಈతDI
• DI Container
੩తDI
• Initializer(Constructor) Injection
• Property(Setter) Injection
• Cake Pattern
• Reader Monad
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Reader Monad
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ؔϞφυ
(Input) -> Element ͷϥούʔ
struct Reader {
typealias WorkFactory = (Input) -> Element
private let workFactory: WorkFactory
func execute(_ input: Input) -> Element {
return workFactory(input)
}
}
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map / flatMap
func map(_ f: @escaping (Element) -> T) -> Reader {
return Reader { input in
f(self.execute(input))
}
}
func flatMap(_ f: @escaping (Element) -> Reader) -> Reader {
return Reader { input in
f(self.execute(input)).execute(input)
}
}
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ఆٛ͜Μ͚ͩ
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ex.
let plusTwoReader = Reader { $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 { y in x * y } }
.execute(3) // 18
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ධՁ͢Δ·Ͱɺ
Πϯϓοτ(ґଘ)Λ
Ԇͤ͞Δ͜ͱ͕Ͱ͖Δ
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Example DI
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ex.
!
protocol UserServiceType {
func find(by id: User.Id) -> User?
}
struct UserService: UserServiceType {
func find(by id: User.Id) -> User? { ... }
}
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ex.
!
Dependency
protocol Module {
var userService: UserServiceType { get }
var tweetService: TweetServiceType { get }
}
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ex.
!
Client
func getTweets(by userId: User.Id) -> Reader {
return Reader { module in
module.userService.find(by: userId)
.map { $0.name }
.map { module.tweetService.findAll(by: $0) }
?? []
}
}
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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]
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DI with Reader Monad
Pros
• ΦϒδΣΫτ୯ҐͰͳ͘ɺؔ୯Ґͷࡉ͔ͳDI͕ग़དྷΔ
Cons
• ReaderܕʹϩοΫΠϯ͞ΕΔ
• ͍͠
• ґଘ͕ෳʹͳΔͱѻ͍ʹ͍͘
• Ϟφυ͕ωετͨ࣌͠ͷѻ͍͕ʹͳΔ
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Conclusion
• DIख๏ͷҰͭʹReader MonadΛ༻ͨ͠ํ๏
͕͋Δ
• SwiftͰѻ͏ʹ࣮༻ݫ͍͠ҹ
• functional-programmingΛಥ͖ਐΊΔڧ
͍ҙࢤͱ֮ޛ͕͋Ε...
• ༷ʑͳDIख๏͕͋Δ͕ɺίϯςΩετ
(ϝϯόɾจԽ)ʹԠͨ͡ͷΛબ͠·͠ΐ͏ʂ
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https://github.com/
to4iki/Reader
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Thanks
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