Mixins over Inheritance — AppDevCon'17

My talk about using Mixins in Swift @ AppDevCon 2017

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Embark in a journey with some Sci-Fi characters to discover how the Mixins & Traits pattern can help you better design your Swift code, avoid multiple-inheritance problems, and propose a protocol-oriented, Crusty-approved™ alternative to composition!

In this talk you’ll discover what Mixins & Traits are, and how they can help you solve some interesting problems and make your architecture more flexible. Using some concrete examples, we’ll see also how these can be used in everyday challenges.

By digging even further and leveraging things like generics, type inference and POP, we’ll even be able to bring some more magic to our code and make it safer, also allowing us to get rid of String-based API and letting the compiler do all the job for us!

Transcript

1. Mixins over Inheritance
   Leveraging Mixins and Traits in Swift
   Olivier Halligon
   March 2017
   aligatr
   

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2. aligatr
   Bonjour!
   • iOS Architect & Lead Dev @ Niji
   • Teaching, Sharing, Speaking

   http://alisoftware.github.io 

   @aligatr
   • OpenSource enthusiast

   http://github.com/AliSoftware

   OHHTTPStubs, SwiftGen, Reusable, CocoaPods, Fastlane
   !"
   #✍
   %&
   '(
   

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3. aligatr
   Sci-Fi!
   

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4. aligatr
   Sci-Fi!
   Doc Emmett Brown
   Doctor Who
   Iron Man
   Superman
   Time Traveler
   Flyer
   Human
   Alien
   

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5. aligatr
   Inheritance?
   Doc Emmett Brown Doctor Who
   Iron Man Superman
   Human Alien
   Character
   

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6. aligatr
   Inheritance?
   Doc Emmett Brown Doctor Who
   Iron Man Superman
   Time Traveler Flyer
   Human Alien
   Character
   

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7. aligatr
   Composition!
   Doc Emmett Brown
   Doctor Who
   Iron Man
   Superman
   Time Machine
   Human Traits
   Alien Traits
   Flying Engine
   Flying Engine
   Time Machine
   Human Traits
   Alien Traits
   

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8. aligatr
   Composition!
   class DoctorWho {
   let traits: AlienTraits
   let tardis: TimeMachine
   let name: String
   init(name: String, planet: String = "Gallifrey") {
   self.traits = AlienTraits(planet: planet, hearts: 2)
   self.tardis = TimeMachine()
   self.name = name
   }
   }
   class TimeMachine {
   func travel(to date: Date) {
   print(")* \(date) +,")
   }
   }
   struct AlienTraits {
   let planet: String
   let hearts: Int
   }
   

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9. aligatr
   Composition!
   let david = DoctorWho()
   david.tardis.travel(to: Date(timeIntervalSince1970: 1303484520))
   // )* Apr 22, 2011, 5:02 PM +,
   print(david.traits.hearts)
   // 2
   let clark = SuperMan()
   clark.flyingEngine.fly() // flyingEngine?!
   !
   -
   .
   

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10. aligatr
    Mixins?
    Doc Emmett Brown
    Doctor Who
    Iron Man
    Superman
    Time Traveler
    Flyer
    Human
    Alien
    Identity / 0 Abilities
    

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11. aligatr
    Protocols with Default Implementation
    protocol Flyer {
    func fly()
    }__
    extension Flyer {
    func fly() {
    print("I believe I can flyyyyy ⽄")
    }__
    }__
    

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12. aligatr
    Protocols with Default Implementation
    protocol Flyer {
    func fly()
    }__
    extension Flyer {
    func fly() {
    print("I believe I can flyyyyy ⽄")
    }__
    }__
    class SuperMan: Flyer {
    // let Clark sing!
    }
    class Bird: Flyer {
    // we get the default implementation of fly() here
    }
    class Plane: Flyer {
    // we get the default implementation of fly() here
    }
    I believe
    I can flyyyyy ⽄
    

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13. aligatr
    Protocols with Default Implementation
    protocol Flyer {
    func fly()
    }__
    extension Flyer {
    func fly() {
    print("I believe I can flyyyyy ⽄")
    }__
    }__
    class IronMan: Flyer {
    let thrusters = Thrusters()
    // specific implementation when needed
    func fly() {
    thrusters.start()
    }
    }
    

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14. aligatr
    Unlimited Abilities 0
    protocol TimeTraveler {
    func travel(to date: Date)
    }
    extension TimeTraveler {
    func travel(to date: Date) {
    print(")* \(date) +,")
    }
    }
    protocol Flyer {
    func fly()
    }__
    extension Flyer {
    func fly() {
    print("I believe I can flyyyyy ⽄")
    }
    }
    • • •
    

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15. aligatr
    One Identity, Multiple Abilities
    class TimeLord: Alien, TimeTraveler, Flyer {
    init() {
    super.init(name: "I'm the Doctor", planet: "Gallifrey")
    }
    }
    let doctorWho = TimeLord()
    doctorWho.travel(to: Date(timeIntervalSince1970: 1303484520))
    // )* Apr 22, 2011, 5:02 PM +,
    doctorWho.fly()
    

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16. aligatr
    Adding Abilities
    extension TimeLord: SpaceTraveler {}
    extension Superman: SpaceTraveler {}
    protocol SpaceTraveler {
    func travel(to location: String)
    }
    extension SpaceTraveler {
    func travel(to location: String) {
    print("Let's go to \(location)!")
    }
    }
    doctorWho.travel(to: "Trenzalore")
    // prints "Let's go to Trenzalore!"
    

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17. aligatr
    Protocol All the Things!
    struct TimeLord: Alien, TimeTraveler, Flyer, SpaceTraveler {
    let name = "I'm the Doctor"
    let planet = "Gallifrey"
    }
    protocol Named {
    var name: String { get }
    }
    protocol Alien: Named {
    var planet: String { get }
    }
    class Character {
    let name: String
    init(name: String) { … }
    }
    class Alien: Character {
    let planet: String
    init(name: String, planet: String) { … }
    }
    « Protocol Oriented Programming is Not a Silver Bullet »
    — Chris Eidhof
    

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18. aligatr
    Back to Boring Reality
    class SuperSmartViewController: UIViewController,
    BurgerMenuProvider, Animatable, CustomTitleViewProvider
    {
    …
    }
    extension SuperSmartViewController: Themable { }
    let vc = SuperSmartViewController()
    vc.apply(theme: .dark)
    

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19. aligatr
    Creating type-safe APIs
    

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20. aligatr
    Creating type-safe APIs
    let cell1 =
    tableView.dequeueReusableCell(withIdentifier: "CustomCellOne",
    for: indexPath) as! CustomCellOne
    cell1.fill(withText: "Model One, \(indexPath.row)")
    class CustomCellOne: UITableViewCell {
    func fill(withText: String) { }
    }
    class CustomCellTwo: UITableViewCell {
    func fill(withIndex: Int) { }
    }
    

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21. aligatr
    Creating type-safe APIs
    protocol Reusable: class {
    static var reuseIdentifier: String { get }
    }
    extension Reusable {
    static var reuseIdentifier: String {
    return String(describing: Self.self)
    }
    }
    let cell1 =
    tableView.dequeueReusableCell(withIdentifier: CustomCellOne.reuseIdentifier,
    for: indexPath) as! CustomCellOne
    cell1.fill(withText: "Model One, \(indexPath.row)")
    class CustomCellOne: UITableViewCell, Reusable {
    func fill(withText: String) { }
    }
    class CustomCellTwo: UITableViewCell, Reusable {
    func fill(withIndex: Int) { }
    }
    

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22. aligatr
    Creating type-safe APIs
    protocol Reusable: class {
    static var reuseIdentifier: String { get }
    }
    extension Reusable {
    static var reuseIdentifier: String {
    return String(describing: Self.self)
    }
    }
    extension UITableView {
    func dequeueReusableCell(indexPath: IndexPath) -> T {
    return self.dequeueReusableCell(withIdentifier: T.reuseIdentifier,
    for: indexPath) as! T
    }
    }
    class CustomCellOne: UITableViewCell, Reusable {
    func fill(withText: String) { }
    }
    class CustomCellTwo: UITableViewCell, Reusable {
    func fill(withIndex: Int) { }
    }
    

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23. aligatr
    Creating type-safe APIs
    protocol Reusable: class {
    static var reuseIdentifier: String { get }
    }
    extension Reusable {
    static var reuseIdentifier: String {
    return String(describing: Self.self)
    }
    }
    extension UITableView {
    func dequeueReusableCell(indexPath: IndexPath) -> T where T: UITableViewCell, T: Reusable {
    return self.dequeueReusableCell(withIdentifier: T.reuseIdentifier,
    for: indexPath) as! T
    }
    }
    class CustomCellOne: UITableViewCell, Reusable {
    func fill(withText: String) { }
    }
    class CustomCellTwo: UITableViewCell, Reusable {
    func fill(withIndex: Int) { }
    }
    

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24. aligatr
    Creating type-safe APIs
    extension UITableView {
    func dequeueReusableCell(indexPath: IndexPath) -> T where T: UITableViewCell, T: Reusable {
    return self.dequeueReusableCell(withIdentifier: T.reuseIdentifier,
    for: indexPath) as! T
    }
    }
    let cell1 = tableView.dequeueReusableCell(indexPath: indexPath)
    cell1.fill(withText: "Model One, \(indexPath.row)")
    error: generic parameter 'T' could not be inferred
    

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25. aligatr
    Creating type-safe APIs
    extension UITableView {
    func dequeueReusableCell(indexPath: IndexPath) -> T where T: UITableViewCell, T: Reusable {
    return self.dequeueReusableCell(withIdentifier: T.reuseIdentifier,
    for: indexPath) as! T
    }
    }
    let cell1: CustomCellOne = tableView.dequeueReusableCell(indexPath: indexPath)
    cell1.fill(withText: "Model One, \(indexPath.row)")
    

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26. aligatr
    Creating type-safe APIs
    extension UITableView {
    func dequeueReusableCell(indexPath: IndexPath) -> T where T: UITableViewCell, T: Reusable {
    return self.dequeueReusableCell(withIdentifier: T.reuseIdentifier,
    for: indexPath) as! T
    }
    }
    let cell1: CustomCellOne = tableView.dequeueReusableCell(indexPath: indexPath)
    cell1.fill(withText: "Model One, \(indexPath.row)")
    let cell2 = tableView.dequeueReusableCell(indexPath: indexPath) as CustomCellTwo
    cell2.fill(withIndex: indexPath.row)
    

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27. aligatr
    Creating type-safe APIs
    class CustomCellOne: UITableViewCell, Reusable {
    func fill(withText: String) { }
    }
    class CustomCellTwo: UITableViewCell, Reusable {
    func fill(withIndex: Int) { }
    }
    let cell1: CustomCellOne = tableView.dequeueReusableCell(indexPath: indexPath)
    cell1.fill(withText: "Model One, \(indexPath.row)")
    let cell2 = tableView.dequeueReusableCell(indexPath: indexPath) as CustomCellTwo
    cell2.fill(withIndex: indexPath.row)
    

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28. aligatr
    Thank You!
    protocol Talk {
    func ask(question: String) -> String
    }
    extension Talk {
    func ask(question: String) -> String {
    return "ya tu sabes"
    }
    }
    http://alisoftware.github.io
    https://twitter.com/aligatr
    http://github.com/AliSoftware/Reusable
    ✍
    March 2017
    Olivier Halligon
    I believe
    I can flyyyyy ⽄
    

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