Translations

S.O.L.I.D.

🔐 The Single Responsibility Principle

protocolOpenable{mutatingfunc open()}protocolCloseable{mutatingfunc close()}// I'm the door. I have an encapsulated state and you can change it using methods.structPodBayDoor:Openable,Closeable{privateenumState{case opencase closed}privatevarstate:State=.closedmutatingfunc open(){        state=.open}mutatingfunc close(){        state=.closed}}// I'm only responsible for opening, no idea what's inside or how to close.finalclassDoorOpener{privatevardoor:Openableinit(door:Openable){self.door= door}func execute(){        door.open()}}// I'm only responsible for closing, no idea what's inside or how to open.finalclassDoorCloser{privatevardoor:Closeableinit(door:Closeable){self.door= door}func execute(){        door.close()}}letdoor=PodBayDoor() // ⚠️ Only the `DoorOpener` is responsible for opening the door.letdoorOpener=DoorOpener(door: door)doorOpener.execute()// ⚠️ If another operation should be made upon closing the door,// like switching on the alarm, you don't have to change the `DoorOpener` class.letdoorCloser=DoorCloser(door: door)doorCloser.execute()

✋ The Open Closed Principle

protocolShooting{func shoot()->String}// I'm a laser beam. I can shoot.finalclassLaserBeam:Shooting{func shoot()->String{return"Ziiiiiip!"}}// I have weapons and trust me I can fire them all at once. Boom! Boom! Boom!finalclassWeaponsComposite{letweapons:[Shooting]init(weapons:[Shooting]){self.weapons= weapons}func shoot()->[String]{return weapons.map{ $0.shoot()}}}letlaser=LaserBeam()varweapons=WeaponsComposite(weapons:[laser])weapons.shoot()// I'm a rocket launcher. I can shoot a rocket.// ⚠️ To add rocket launcher support I don't need to change anything in existing classes.finalclassRocketLauncher:Shooting{func shoot()->String{return"Whoosh!"}}letrocket=RocketLauncher()weapons=WeaponsComposite(weapons:[laser, rocket])weapons.shoot()

👥 The Liskov Substitution Principle

letrequestKey:String="NSURLRequestKey"// I'm a NSError subclass. I provide additional functionality but don't mess with original ones.classRequestError:NSError{varrequest:NSURLRequest?{returnself.userInfo[requestKey]as?NSURLRequest}}// I fail to fetch data and will return RequestError.func fetchData(request:NSURLRequest)->(data:NSData?, error:RequestError?){letuserInfo:[String:Any]=[requestKey: request]return(nil,RequestError(domain:"DOMAIN", code:0, userInfo: userInfo))}// I don't know what RequestError is and will fail and return a NSError.func willReturnObjectOrError()->(object:AnyObject?, error:NSError?){letrequest=NSURLRequest()letresult=fetchData(request: request)return(result.data, result.error)}letresult=willReturnObjectOrError()// Ok. This is a perfect NSError instance from my perspective.leterror:Int?= result.error?.code// ⚠️ But hey! What's that? It's also a RequestError! Nice!iflet requestError= result.erroras?RequestError{    requestError.request}

🍴 The Interface Segregation Principle

// I have a landing site.protocolLandingSiteHaving{varlandingSite:String{get}}// I can land on LandingSiteHaving objects.protocolLanding{func land(on:LandingSiteHaving)->String}// I have payload.protocolPayloadHaving{varpayload:String{get}}// I can fetch payload from vehicle (ex. via Canadarm).protocolPayloadFetching{func fetchPayload(vehicle:PayloadHaving)->String}finalclassInternationalSpaceStation:PayloadFetching{    // ⚠ Space station has no idea about landing capabilities of SpaceXCRS8.func fetchPayload(vehicle:PayloadHaving)->String{return"Deployed\(vehicle.payload) at April 10, 2016, 11:23 UTC"}}// I'm a barge - I have landing site (well, you get the idea).finalclassOfCourseIStillLoveYouBarge:LandingSiteHaving{letlandingSite="a barge on the Atlantic Ocean"}// I have payload and can land on things having landing site.// I'm a very limited Space Vehicle, I know.finalclassSpaceXCRS8:Landing,PayloadHaving{letpayload="BEAM and some Cube Sats"    // ⚠️ CRS8 knows only about the landing site information.func land(on:LandingSiteHaving)->String{return"Landed on\(on.landingSite) at April 8, 2016 20:52 UTC"}}letcrs8=SpaceXCRS8()letbarge=OfCourseIStillLoveYouBarge()letspaceStation=InternationalSpaceStation()spaceStation.fetchPayload(vehicle: crs8)crs8.land(on: barge)

🔝 The Dependency Inversion Principle

protocolTimeTraveling{func travelInTime(time:TimeInterval)->String}finalclassDeLorean:TimeTraveling{func travelInTime(time:TimeInterval)->String{return"Used Flux Capacitor and travelled in time by:\(time)s"}}finalclassEmmettBrown{privatelettimeMachine:TimeTraveling    // ⚠️ Emmet Brown is given a `TimeTraveling` device, not the concrete class `DeLorean`!init(timeMachine:TimeTraveling){self.timeMachine= timeMachine}func travelInTime(time:TimeInterval)->String{return timeMachine.travelInTime(time: time)}}lettimeMachine=DeLorean()letmastermind=EmmettBrown(timeMachine: timeMachine)mastermind.travelInTime(time:-3600*8760)

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