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Lens introduction
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to4iki
February 18, 2018
Programming
0
530
Lens introduction
in `swift` implementation
see:
https://github.com/to4iki/LensKit
to4iki
February 18, 2018
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Transcript
Lens Shinjuku.LT#17 @to4iki 1
Me • Takezawa • • ! • ☕ •
♨ 2
what Lens? 3
Def. / Feature • getter/setterͷநԽɾম͖͠(൚༻Խ) • ༷ʑͳσʔλΛڞ௨ͷI/FͰૢ࡞Ͱ͖Δ • ಛఆͷݴޠʹґଘ͠ͳ͍֓೦/ܕ •
functional • ෆมߏ / ߹Մೳ • Lens Laws 4
ekmett/lens 5
• Monocle.Lens - elm-monocle • julien-truffaut/Monocle 6
https://github.com/julien-truffaut/Monocle/blob/master/image/class- diagram.png 7
getter setter 8
getter • ΦϒδΣΫτS͔ΒAΛऔΓग़͢ • get: (S) -> A setter •
ΦϒδΣΫτSͷҙͷΛAʹมߋ͢Δ • set: (S, A) -> S == set: (S) -> A -> S 9
͜ΕΒͷ͍͢͝ getter/setter1Λ ҙͷΦϒδΣΫτͷ ҙͷϝϯόʹద༻͢Δͷ͕ Lens 1 https://qiita.com/to4iki/items/f0cc28e1102cf53be85d 10
࣮ͯ͠ΈΔ 11
struct Lens<S, T> { private let _get: (S) -> T
private let _set: (S, T) -> S init(get: @escaping (S) -> T, set: @escaping (S, T) -> S) func get(_ source: S) -> T func set(_ source: S, value: T) -> S } 12
͜Μ͚ͩ 13
struct User { let name: String } let user =
User(name: "hoge") let nameLens = Lens<User, String>( get: { $0.name }, set: { User(name: $1) } ) nameLens.get(user) // "hoge" nameLens.set("fuga") // User(name:"fuga)" 14
Usecase? 15
ωετͨ͠σʔλͷ͋ΔҰ෦ ͚ͩΛมߋ͍ͨ͠ struct Street { let name: String } struct
Address { let street: Street } struct Company { let address: Address } struct Employee { let company: Company } let employee = Employee(company: Company(address: Address(street: Street(name: "street")))) 16
! let updatedEmployee = Employee(company: Company(address: Address(street: Street(name: employee.company.address.street.name.capitalizedString) )
) ) 17
Lens߹Λ͍ɺ ෆมߏΛอͪͳ͕Β ΞΫηεग़དྷΔ 18
struct Lens<S, T> { ... func compose<U>(_ other: Lens<T, U>)
-> Lens<S, U> { return Lens<S, U>( get: { (source: S) -> U in other.get(self.get((source))) }, set: { (source: S, value: U) -> S in self.set(source, value: other.set(self.get(source), value: value)) } ) } } 19
(operatorఆٛ͠ͱ͘) /// Left-to-Right Composition infix operator >>> : MultiplicationPrecedence func
>>> <S, T, U>(lhs: Lens<S, T>, rhs: Lens<T, U>) -> Lens<S, U> { return lhs.compose(rhs) } 20
Demo 21
! let nameLens = Lens<Street, String>(get: { $0.name }, set:
{ Street(name: $1) } ) let streetLens = Lens<Address, Street> ... let addressLens = Lens<Company, Address> ... let companyLens = Lens<Employee, Company> ... let lens: Lens<Employee, String> = companyLens >>> addressLens >>> streetLens >>> nameLens let employee = Employee(company: Company(address: Address(street: Street(name: "street")))) let updatedEmployee = lens.modify(employee) { $0.capitalized } // Employee(Company(Address(Street(name: "Street") 22
https://github.com/ to4iki/LensKit 23
Conclusion • Lens ͍͢͝getter/setter • ෆมߏΛอͪͳ͕Β • ਂ͍ߏͰ •
ʹΞΫηεग़དྷΔ • Ϣʔεέʔεਖ਼͍͠ • ςετ࣌ͷαϙʔτͱͯ͠͏? 24
See also • ࠓ͔Β࢝ΊΔ Lens/Prism 25