Flexible Code for Generic Collections

Presented at Swift Summit on 11/7/2016

Transcript

1. Flexible Code for
   Generic Collections
   Nate Cook @nnnnnnnn
   

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2. The standard library
   collections system
   (Nate’s favorite part of Swift)
   

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3. Protocols in
   Objective-C
   

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4. Protocols in
   Swift
   

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5. 1. A problem
   2.Why it happens
   3.What to do about it
   

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6. struct Brick {
   let color: UIColor
   let size: (w: Int, h: Int)
   }
   

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7. struct Brick {
   let color: UIColor
   let size: (w: Int, h: Int)
   }
   let redSquare = Brick(color: .red, size: (2, 2))
   let orangeSquare = Brick(color: .orange, size: (2, 2))
   

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8. struct Brick {
   let color: UIColor
   let size: (w: Int, h: Int)
   }
   let redSquare =
   let orangeSquare =
   

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9. struct Brick {
   let color: UIColor
   let size: (w: Int, h: Int)
   }
   let bricks = [ , , , , , , ]
   

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10. func createBrickPDF(_ bricks: [Brick]) -> Data {
    let result = NSMutableData()
    // prepare PDF context
    for brick in bricks {
    // generate PDF data
    }
    return result as Data
    }
    

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11. let bricks = [ , , , , , , ]
    let pdfData = createBrickPDF(bricks)
    // Success!
    

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12. !"#
    

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13. let bricks = [ , , , , , , ]
    let firstFiveBricks = bricks.prefix(5)
    

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14. let bricks = [ , , , , , , ]
    let firstFiveBricks = bricks.prefix(5)
    Wow
    such swift
    so declarativ
    wow
    

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15. let bricks = [ , , , , , , ]
    let firstFiveBricks = bricks.prefix(5)
    let pdfData = createBrickPDF(firstFiveBricks)
    Cannot convert value of type ‘ArraySlice’ to expected argument type ‘[Brick]’
    !
    

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16. $%&
    

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17. let bricks = [ , , , , , , ]
    let firstFiveBricks = bricks.prefix(5)
    let pdfData = createBrickPDF(firstFiveBricks)
    Cannot convert value of type ‘ArraySlice’ to expected argument type ‘[Brick]’
    !
    

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18. , , , , , ]
    ks = bricks.prefix(5)
    ateBrickPDF(firstFiveBricks)
    convert value of type ‘ArraySlice’ to expected argum
    

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19. DF(firstFiveBrick
    type ‘ArraySlice’ to exp
    

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20. (˽°□°)˽
    Ɨ ʇɟıʍs
    

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21. let bricks = [ , , , , , , ]
    let firstFiveBricks = bricks.prefix(5)
    let pdfData = createBrickPDF(firstFiveBricks)
    Cannot convert value of type ‘ArraySlice’ to expected argument type ‘[Brick]’
    !
    

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22. let bricks = [ , , , , , , ]
    let firstFiveBricks = bricks.prefix(5)
    let pdfData = createBrickPDF(Array(firstFiveBricks))
    

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23. let bricks = [ , , , , , , ]
    let firstFiveBricks = bricks.prefix(5)
    let pdfData = createBrickPDF(Array(firstFiveBricks))
    // '☕
    

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24. 1. A problem
    2.Why it happens
    3.What to do about it
    

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25. let middleBricks = bricks[2..<5]
    // ArraySlice
    let lastThreeBricks = bricks.suffix(3)
    // ArraySlice
    let bricksAfterFirstTwo = bricks.dropFirst(2)
    // ArraySlice
    

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26. let backwardsBricks = bricks.reversed()
    // ReversedRandomAccessCollection<[Brick]>
    let squareBrickColors = bricks.lazy
    .filter { $0.isSquare }
    .map { $0.color }
    // LazyMapBidirectionalCollection
    // , UIColor>
    

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27. Collection
    wrappers
    

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28. LazySequence MutableBidirectionalSlice LazyBidirectionalCollection
    ReversedRandomAccessCollection EnumeratedSequence FlattenCollection
    LazyMapSequence LazyFilterBidirectionalCollection AnyBidirectionalCollection
    MutableRangeReplaceableBidirectionalSlice LazyMapBidirectionalCollection
    LazyCollection BidirectionalSlice AnyRandomAccessCollection ArraySlice
    FlattenBidirectionalCollection Zip2Sequence MutableSlice AnyCollection
    AnySequence RangeReplaceableBidirectionalSlice JoinedSequence
    LazyMapRandomAccessCollection LazyFilterCollection LazyMapCollection
    MutableRangeReplaceableRandomAccessSlice RandomAccessSlice
    RangeReplaceableSlice LazyFilterSequence LazyRandomAccessCollection
    MutableRangeReplaceableSlice RangeReplaceableRandomAccessSlice
    FlattenSequence ReversedCollection MutableRandomAccessSlice
    

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29. LazySequence MutableBidirectionalSlice LazyBidirectionalCollection
    ReversedRandomAccessCollection EnumeratedSequence FlattenCollection
    LazyMapSequence LazyFilterBidirectionalCollection AnyBidirectionalCollection
    MutableRangeReplaceableBidirectionalSlice LazyMapBidirectionalCollection
    LazyCollection BidirectionalSlice AnyRandomAccessCollection ArraySlice
    FlattenBidirectionalCollection Zip2Sequence MutableSlice AnyCollection
    AnySequence RangeReplaceableBidirectionalSlice JoinedSequence
    LazyMapRandomAccessCollection LazyFilterCollection LazyMapCollection
    MutableRangeReplaceableRandomAccessSlice RandomAccessSlice
    RangeReplaceableSlice LazyFilterSequence LazyRandomAccessCollection
    MutableRangeReplaceableSlice RangeReplaceableRandomAccessSlice
    FlattenSequence ReversedCollection MutableRandomAccessSlice
    

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30. Brought to you by
    Brick-o-Vision™
    

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31. let bricks = [ , , , , , , ]
    

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32. let bricksCopy = Array(bricks.prefix(5))
    

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33. let firstFiveBricks = bricks.prefix(5)
    

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34. 1. A problem
    2.Why it happens
    3.What to do about it
    

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35. Collection
    protocols
    

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36. Sequence
    Collection
    MutableCollection RangeReplaceableCollection
    BidirectionalCollection
    Array ArraySlice
    RandomAccessCollection
    

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37. Sequence
    Collection
    MutableCollection RangeReplaceableCollection
    BidirectionalCollection
    Array ArraySlice
    RandomAccessCollection
    

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38. A series of values
    we access one at a time
    

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39. Sequence protocol
    for brick in bricks {
    print(brick)
    }
    // , , , , , ,
    

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40. Sequence protocol
    for brick in bricks.prefix(5) {
    print(brick)
    }
    // , , , ,
    for number in 1..<10 {
    print(number)
    }
    // 1, 2, 3, 4, 5, 6, 7, 8, 9
    

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41. Sequence protocol
    bricks.contains(where: { $0.color == .blue })
    // true
    bricks.first(where: { $0.color == .blue })
    // Optional( )
    [2, 4, 5, 3, 7, 2, 9].max()
    // Optional(9)
    

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42. Sequence protocol
    (1..<10).map({ "\($0)" })
    // ["1", "2", "3", "4", "5", "6", "7", "8", "9"]
    (1..<10).filter({ $0 % 2 == 0 })
    // [2, 4, 6, 8]
    (1..<10).reduce(0, +)
    // 45
    

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43. Sequence
    Collection
    MutableCollection RangeReplaceableCollection
    BidirectionalCollection
    Array ArraySlice
    RandomAccessCollection
    

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44. Collection protocol
    bricks[1]
    //
    if let i = bricks.index(where: { $0.color == .blue }) {
    print(i, bricks[i])
    }
    // 4,
    bricks.count
    // 7
    

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45. Sequence
    Collection
    MutableCollection RangeReplaceableCollection
    BidirectionalCollection
    Array ArraySlice
    RandomAccessCollection
    

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46. Sequence
    Collection
    MutableCollection RangeReplaceableCollection
    BidirectionalCollection
    Array ArraySlice
    RandomAccessCollection
    IteratorProtocol
    

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47. Iterator of a sequence
    for brick in bricks {
    print(brick)
    }
    // , , , , , ,
    

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48. Iterator of a sequence
    for brick in bricks {
    print(brick)
    }
    // , , , , , ,
    var iterator = bricks.makeIterator()
    while let brick = iterator.next() {
    print(brick)
    }
    // , , , , , ,
    

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49. func createBrickPDF(_ bricks: [Brick]) -> Data {
    let result = NSMutableData()
    // prepare PDF context
    for brick in bricks {
    // generate PDF data
    }
    return result as Data
    }
    

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50. func createBrickPDF(_ bricks: [Brick]) -> Data {
    let result = NSMutableData()
    // prepare PDF context
    for brick in bricks {
    // generate PDF data
    }
    return result as Data
    }
    

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51. func createBrickPDF(_ bricks: S) -> Data
    where S.Iterator.Element == Brick
    {
    let result = NSMutableData()
    // prepare PDF context
    for brick in bricks {
    // generate PDF data
    }
    return result as Data
    }
    

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52. func createBrickPDF(_ bricks: S) -> Data
    where S.Iterator.Element == Brick
    {
    let result = NSMutableData()
    // prepare PDF context
    for brick in bricks {
    // generate PDF data
    }
    return result as Data
    }
    

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53. func createBrickPDF(_ bricks: S) -> Data
    where S.Iterator.Element == Brick
    {
    let result = NSMutableData()
    // prepare PDF context
    for brick in bricks {
    // generate PDF data
    }
    return result as Data
    }
    

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54. Value of type ’S’ has no member ‘count’
    !
    func createBrickPDF(_ bricks: S) -> Data
    where S.Iterator.Element == Brick
    {
    let result = NSMutableData()
    // prepare PDF context
    let renderer = BrickPDFRenderer(count: bricks.count)
    for brick in bricks {
    // generate PDF data
    }
    return result as Data
    }
    

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55. func createBrickPDF(_ bricks: C) -> Data
    where C.Iterator.Element == Brick
    {
    let result = NSMutableData()
    // prepare PDF context
    let renderer = BrickPDFRenderer(count: bricks.count)
    for brick in bricks {
    // generate PDF data
    }
    return result as Data
    }
    

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56. func createBrickPDF(_ bricks: S) -> Data
    where S.Iterator.Element == Brick
    { ... }
    let bricks = [ , , , , , , ]
    let firstFiveBricks = bricks.prefix(5)
    let pdfData = createBrickPDF(firstFiveBricks)
    // Success!!
    

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57. !"#❤*✨!"
    ❤*✨!"#❤*
    ✨!"#❤*✨!
    "#❤*✨!"#
    

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58. Storing generic
    collections
    

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59. Generic type
    class BrickRenderer
    where C.Iterator.Element == Brick
    {
    let bricks: C
    init(_ bricks: C) {
    self.bricks = bricks
    }
    }
    

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60. Type erasure
    class BrickRenderer {
    let bricks: AnyCollection
    init(_ bricks: AnyCollection) {
    self.bricks = bricks
    }
    }
    

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61. Type erasure
    class BrickRenderer {
    let bricks: AnyCollection
    init(_ bricks: AnyCollection) {
    self.bricks = bricks
    }
    }
    let renderer = BrickRenderer(AnyCollection(bricks))
    let renderer =
    BrickRenderer(AnyCollection(firstFiveBricks))
    

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62. Type-specific
    extensions
    

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63. extension Array where Element == Bool {
    func allTrue() -> Bool {
    for x in self {
    if !x {
    return false
    }
    }
    return true
    }
    }
    

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64. extension Array where Element == Bool {
    func allTrue() -> Bool {
    for x in self {
    if !x {
    return false
    }
    }
    return true
    }
    }
    Same-type requirement makes generic parameter 'Element' non-generic
    !
    

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65. extension Sequence where Iterator.Element == Bool {
    func allTrue() -> Bool {
    for x in self {
    if !x {
    return false
    }
    }
    return true
    }
    }
    

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66. Syntax & Naming
    

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67. func createBrickPDF(_ bricks: S) -> Data
    where S.Iterator.Element == Brick
    Swift 3
    func createBrickPDFwhere S.Generator.Element == Brick>
    (_ bricks: S) -> NSData
    Swift 2
    

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68. Thanks!
    "@" + repeatElement("n", count: 8).joined()
    

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