Dependency Injection - Speaker Deck

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!ZPJDIJUHZ Dependency Injection Yoichi Tagaya DevFest Baltics, 16 November, 2018

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!ZPJDIJUHZ Yoichi Tagaya, from Tokyo, Japan About me

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!ZPJDIJUHZ Tokyo evening view 1IPUPCZ D 5PNP:VO IUUQXXXZVOQIPUPOFU

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!ZPJDIJUHZ About me as Swinject author • Swinject: dependency injection framework for Swift • Maintained by 5 members • Recently by Jakub Vano especially! • 2,7k+ GitHub stars now and 1k clones everyday • 4 extensions provided

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!ZPJDIJUHZ Agenda • Software architecture • Dependency injection (DI) • Swinject (DI container)

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!ZPJDIJUHZ What is software architecture

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!ZPJDIJUHZ What is software architecture IUUQTXXXJCNDPNEFWFMPQFSXPSLTSBUJPOBMMJCSBSZGFCFFMFTJOEFYIUNM

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!ZPJDIJUHZ Peter Eeles says An architecture • Defines structure and behavior • Focuses on significant elements • May conform to an architectural style • Influences team structure (inverse Conway maneuver) • Balances stakeholder needs • Is influenced by its environment • Embodies decisions based on rationale

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!ZPJDIJUHZ Architecture is not static but dynamic "SDIJUFDUVSF :FBST TJODFMBVODI &YBNQMFPGBQSPEVDU &OHJOFFST 6TFST L . .

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!ZPJDIJUHZ Architecture is not static but dynamic .7$ "SDIJUFDUVSF :FBST TJODFMBVODI .77. 7*1&3 &YBNQMFPGBQSPEVDU 3*#T &OHJOFFST 6TFST L . .

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!ZPJDIJUHZ Architecture is not static but dynamic $ # " /PX $ /FX# " $ % -BUFS

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!ZPJDIJUHZ Production / unit test $ # " 1SPEVDUJPO 6OJU5FTU .PDLTUVC PG# "

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!ZPJDIJUHZ We need ﬂexibility in architecture

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!ZPJDIJUHZ How to make architecture ﬂexible? Dependency injection!

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!ZPJDIJUHZ Because dependency injection is glue but sticky-like glue 5JHIU$PVQMJOH -PPTF$PVQMJOH

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!ZPJDIJUHZ How to make the sticky-like glue?

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!ZPJDIJUHZ SOLID principles • S - Single responsibility principle • O - Open/closed principle • L - Liskov substitution principle • I - Interface segregation principle • D - Dependency inversion principle • Should not depend on concretions but abstractions

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!ZPJDIJUHZ Depending on concretions / abstractions Depending on concretions (tight coupling) *NQMFNFOUBUJPO $PODSFUF5ZQF Depending on abstractions (loose coupling) 3FGFSFODF *NQMFNFOUBUJPO Protocol (Interface) 3FGFSFODF $PODSFUF5ZQF" $PODSFUF5ZQF#

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!ZPJDIJUHZ Dependency injection: a way to realize dependency inversion principle *NQMFNFOUBUJPO Protocol (Interface) 3FGFSFODF

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!ZPJDIJUHZ Dependency injection: a way to realize dependency inversion principle *NQMFNFOUBUJPO Protocol (Interface) 3FGFSFODF *OTUBODFPG $PODSFUF5ZQF# 1BTT JOKFDU UPJOJUJBMJ[FS

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!ZPJDIJUHZ Dependency injection: a way to realize dependency inversion principle *NQMFNFOUBUJPO Protocol (Interface) 3FGFSFODF $PODSFUF5ZQF# 5IFTZTUFNJTDPOpHVSFE UPVTF$PODSFUF5ZQF#

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!ZPJDIJUHZ Code example of dependency injection protocol APIClientProtocol { ... } class APIClient: APIClientProtocol { ... } let vm = MyViewModel(apiClient: APIClient()) class MyViewModel { let apiClient: APIClientProtocol init(apiClient: APIClientProtocol) { self.apiClient = apiClient } } APIClientProtocol "CTUSBDUUZQF *OKFDUDPODSFUFUZQF

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!ZPJDIJUHZ Try dependency injection with Swinject Register/resolve-style DI container like dictionary

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!ZPJDIJUHZ How to use Swinject container $POUBJOFS Register Resolve

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!ZPJDIJUHZ Code example of registration $POUBJOFS Register import Swinject let container = Container() container.register(MyViewModel.self) { resolver in let apiClient = resolver.resolve(APIClientProtocol.self)! return MyViewModel(apiClient: apiClient) } container.register(APIClientProtocol.self) { _ in APIClient() }

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!ZPJDIJUHZ Code example of resolution $POUBJOFS Resolve import Swinject let vm = container.resolve(MyViewModel.self)!

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!ZPJDIJUHZ In a production app class MyViewModel { init(dep1: D1, dep2: D2, dep3: D3, id: String, name: String) { ... } } .BOZEFQFOEFODJFT %FQFOEFODZJOKFDUJPODPEFJTPGUFOMJLFUIJT

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!ZPJDIJUHZ In a production app class MyViewModel { init(dep1: D1, dep2: D2, dep3: D3, id: String, name: String) { ... } } .BOZEFQFOEFODJFT 3VOUJNFQBSBNFUFST PUIFSUIBOEFQFOEFODJFT %FQFOEFODZJOKFDUJPODPEFJTPGUFOMJLFUIJT

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!ZPJDIJUHZ Using typealias of dependency tuple init(dependency: Dependency, id: String, name: String) 5ZQFBMJBTPGUVQMF % % % %FQFOEFODZ 1BSBNFUFST

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!ZPJDIJUHZ Example of class deﬁnition with typealias of tuple protocol APIClientProtocol { ... } class APIClient: APIClientProtocol { ... } protocol LoggerProtocol { ... } class Logger: LoggerProtocol { ... } 5ZQFBMJBTPG EFQFOEFODZUVQMF class MyViewModel { typealias Dependency = ( APIClientProtocol, LoggerProtocol ) let (apiClient, logger): Dependency let id: String init(dependency: Dependency, id: String) { (apiClient, logger) = dependency self.id = id } } &YBNQMFXJUIEFQFOEFODJFTBOEQBSBNFUFS

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!ZPJDIJUHZ DI Registration let container = Container() container.register(APIClientProtocol.self) { _ in APIClient() } container.register(LoggerProtocol.self) { _ in Logger() } $POUBJOFS Register container.register(MyViewModel.self) { (resolver, id: String) in let dependency = ( resolver.resolve(APIClientProtocol.self)!, resolver.resolve(LoggerProtocol.self)! ) return MyViewModel( dependency: dependency, id: id ) }

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!ZPJDIJUHZ DI Resolution let myViewModel = container.resolve( MyViewModel.self, argument: "abc")! $POUBJOFS Resolve

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!ZPJDIJUHZ Easier to see the dependencies and parameters!

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!ZPJDIJUHZ But, still too many “!”s. Is it OK? "

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!ZPJDIJUHZ Let’s try adding another dependency to implement a new feature

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!ZPJDIJUHZ Add another dependency let (apiClient, logger): Dependency let id: String init(dependency: Dependency, id: String) { (apiClient, logger) = dependency self.id = id } } class MyViewModel { typealias Dependency = ( APIClientProtocol, LoggerProtocol )

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!ZPJDIJUHZ Add another dependency protocol DatabaseProtocol { ... } class Database: DatabaseProtocol { ... } let (apiClient, logger): Dependency let id: String init(dependency: Dependency, id: String) { (apiClient, logger) = dependency self.id = id } } class MyViewModel { typealias Dependency = ( APIClientProtocol, LoggerProtocol )

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!ZPJDIJUHZ Add another dependency protocol DatabaseProtocol { ... } class Database: DatabaseProtocol { ... } class MyViewModel { typealias Dependency = ( APIClientProtocol, LoggerProtocol, DatabaseProtocol ) let (apiClient, logger): Dependency let id: String init(dependency: Dependency, id: String) { (apiClient, logger) = dependency self.id = id } }

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!ZPJDIJUHZ Add another dependency protocol DatabaseProtocol { ... } class Database: DatabaseProtocol { ... } class MyViewModel { typealias Dependency = ( APIClientProtocol, LoggerProtocol, DatabaseProtocol ) let (apiClient, logger, database): Dependency let id: String init(dependency: Dependency, id: String) { (apiClient, logger) = dependency self.id = id } } 8SPOHUVQMFIFSF ❕

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!ZPJDIJUHZ Add another dependency protocol DatabaseProtocol { ... } class Database: DatabaseProtocol { ... } class MyViewModel { typealias Dependency = ( APIClientProtocol, LoggerProtocol, DatabaseProtocol ) let (apiClient, logger, database): Dependency let id: String init(dependency: Dependency, id: String) { (apiClient, logger, database) = dependency self.id = id } } 8SPOHUVQMFIFSF ❕

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!ZPJDIJUHZ Add another dependency protocol DatabaseProtocol { ... } class Database: DatabaseProtocol { ... } class MyViewModel { typealias Dependency = ( APIClientProtocol, LoggerProtocol, DatabaseProtocol ) let (apiClient, logger, database): Dependency let id: String init(dependency: Dependency, id: String) { (apiClient, logger, database) = dependency self.id = id } }

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!ZPJDIJUHZ Add another dependency container.register(MyViewModel.self) { (resolver, id: String) in let dependency = ( resolver.resolve(APIClientProtocol.self)!, resolver.resolve(LoggerProtocol.self)! ) return MyViewModel( dependency: dependency, id: id ) } let myViewModel = container.resolve( MyViewModel.self, argument: "abc")!

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!ZPJDIJUHZ Add another dependency container.register(DatabaseProtocol.self) { _ in Database() } $BOOPUDPOWFSU ❕ container.register(MyViewModel.self) { (resolver, id: String) in let dependency = ( resolver.resolve(APIClientProtocol.self)!, resolver.resolve(LoggerProtocol.self)!, resolver.resolve(DatabaseProtocol.self)! ) return MyViewModel( dependency: dependency, id: id ) } let myViewModel = container.resolve( MyViewModel.self, argument: "abc")!

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!ZPJDIJUHZ Add another dependency container.register(DatabaseProtocol.self) { _ in Database() } container.register(MyViewModel.self) { (resolver, id: String) in let dependency = ( resolver.resolve(APIClientProtocol.self)!, resolver.resolve(LoggerProtocol.self)!, resolver.resolve(DatabaseProtocol.self)! ) return MyViewModel( dependency: dependency, id: id ) } let myViewModel = container.resolve( MyViewModel.self, argument: "abc")!

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!ZPJDIJUHZ Just follow what Swift compiler says to add new dependencies!

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!ZPJDIJUHZ Summary • Architecture is not static but dynamic to evolve. • Dependency injection is sticky-like glue. • Use a typealias to group dependencies. • Just follow Swift compiler to add new dependencies.

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!ZPJDIJUHZ More info, thanks! • Swinject Tutorial for iOS: Getting Started by Gemma Barlow at raywenderlich.com • iOS App Development: Design Patterns for Mobile Architecture by Jon Bott at lynda.com • Dependency injection in Swift by Manuel Munoz at blog.quadiontech.com • Adventures in Dependency Swinjection by Ben Dietzkis at medium.com/@topLayoutGuide • Swinject - Dependency Injection in iOS by Iron Ben Zvi at speakerdeck.com/oronbz