Swift Values

Presented at iOS Love Meetup Group

Transcript

1. Swift Values
   

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2. Francisco Díaz
   @fco_diaz
   

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3. Objective-C -> Swift
   NSArray / NSMutableArray
   -> Array
   NSDictionary / NSMutableDictionary
   -> Dictionary
   NSString / NSMutableString
   -> String
   

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4. 4 Differences between Value / Reference Types
   4 Immutability in Swift
   4 Using Value Types
   

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5. Value Type
   

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6. Struct
   struct Point {
   var x: Int, y: Int
   }
   

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7. Copying creates an independent instance with its own unique
   copy of its data
   var a = Point(x: 1, y: 2)
   var b = a // a: {1, 2}; b: {1, 2}
   b.x = 3 // a: {1, 2}; b: {3, 2}
   

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8. Reference Type
   

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9. Class
   class Person {
   var name: String
   init(name: String) {
   self.name = name
   }
   }
   

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10. Copying a reference, on the other hand, implicitly creates a
    shared instance
    let pedro = Person(name: "Pedro")
    var clon = pedro // pedro: {"Pedro"}; clon: {"Pedro"}
    clon.name = "Pablo" // pedro: {"Pablo"}; clon: {"Pablo"}
    

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11. Value Types are Immutable
    

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12. What about variables? And mutating functions? Eh?
    Eh? !
    struct Point {
    var x: Int, y: Int
    init(x: Int, y: Int) {
    self.x = x
    self.y = y
    }
    mutating func movePointBy(x: Int, y: Int) {
    self.x += x
    self.y += y
    }
    }
    var a = Point(x: 1, y: 2)
    a.movePointBy(3, y: 3) // a: {4, 5}
    a.x = 20 // a: {20, 5}
    

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13. let a = Point(x: 1, y: 2)
    a.movePointBy(3, y: 3) // Compilation error
    a.x = 20 // Compilation error
    // Immutable value of type 'Point' only has mutating members named 'movePointBy'
    

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14. Using Value Types
    

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15. The Value layer game
    by Andy Matuschak
    

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16. Object layer
    Value layer
    

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17. Prefer structs over classes
    

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18. Constants by default
    struct Point {
    let x: Int, y: Int
    }
    

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19. Use mutability carefully, where it makes
    sense
    struct Meetup {
    let speakers: [String]
    }
    struct Meetup {
    var speakers: [String]
    mutating func addAwesomeSpeaker(speaker: String)
    }
    addAwesomeSpeaker("Francisco") ~== Meetup(speaker: speakers.append("Francisco"))
    

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20. Every Value type should be Equatable
    

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21. Values are inherently equatable
    let a = "Hola "
    let b = "Mundo"
    a == b // false
    "Hola Mundo" == a + b // true
    1 == 2 - 1 // true
    

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22. How?
    struct Point: Equatable {
    let x: Int, y: Int
    }
    func ==(lhs: Point, rhs: Point) -> Bool {
    return lhs.x == rhs.x && lhs.y == rhs.y
    }
    

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23. When to use Classes?
    4 NetworkController1 == NetworkController2 ???
    4 UIKit
    

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24. Example
    

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27. MVVM
    Board Model: Contains data representing a board
    Board VM: Communicates between Model and View
    - Converts model data to be displayed
    - Takes user input and acts on model
    Board View: Displays a board to the user
    Game Scene: Puts it all together.
    

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29. Choose immutability and
    see where it takes you.
    1
    Rich Hickey
    

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30. struct Board {
    let cells: [Cell]
    }
    struct Cell {
    let value: Int
    }
    

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31. struct BoardViewModel {
    let board: Board
    func cellViewModelAtIndex(index: Int) -> CellViewModel
    }
    struct CellViewModel {
    let cell: Cell
    let index: Int
    func attributes() -> (color: UIColor, texture: SKTexture, ...)
    }
    

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32. class BoardView: SKSpriteNode {
    var cellViews: [CellView] = []
    init(size: CGSize)
    func configure(boardViewModel: BoardViewModel)
    }
    class CellView: SKSpriteNode {
    init(size: CGSize, cellViewModel: CellViewModel)
    func configure(cellViewModel: CellViewModel)
    func scaleBy(scale: CGFloat)
    func animateTouch()
    ...
    }
    

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33. Every time something changes, create a new
    BoardViewModel and pass it to the
    BoardView
    func configure(boardViewModel: BoardViewModel)
    

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35. Only update what changed
    

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36. But how do I know what
    changed?
    

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37. They're Values
    ...and you can compare values easily
    func configure(cellViewModel: CellViewModel) {
    if oldCellViewModel != cellViewModel {
    // update
    }
    }
    

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39. 4 Differences between Value / Reference Types
    4 Immutability in Swift
    4 Using Value Types
    

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40. Resources:
    Swift Blog: Value and Reference Types
    Should I use a Swift struct or a class?
    WWDC 2015: Session 408
    WWDC 2015: Session 414
    The Value of Values by Rich Hickey
    Enemy of the State by Justin Spahr-Summers
    Functioning as a Functionalist by Andy Matuschak
    Immutable Data and React by Lee Byron
    

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41. Thanks!
    Slides available at:
    https://github.com/fdiaz/swift-values-talk
    

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