Controlling Complexity in Swift; or, Making Friends with Value

People tell you that you’re supposed to avoid mutable state, but how can anything happen if you never call a setter? People tell you that you’re supposed to write unit tests, but how can you test a user interaction? People tell you that you’re supposed to make your code reusable, but how can you factor it out of your enormous view controllers?

This talk presents a pragmatic approach to managing complexity in inherently stateful systems. We’ll take the best from the ivory tower and drag it down with us into the muck of the “real world.” You’ll leave with practical strategies for making large swaths of your code stateless and for confining the rest within well-understood boundaries.

Transcript

1. CONTROLLING COMPLEXITY IN SWIFT (or) MAKING FRIENDS WITH VALUE TYPES Andy Matuschak ANDYMATUSCHAK.ORG / @ANDY_MATUSCHAK
2. COMPLEXITY
3. TASTE VS ABILITY
4. FOCUSING OUR PATHS
5. FOCUSING OUR CONTROL FLOW
6. FOCUSING OUR DEPENDENCIES
7. FOCUSING OUR EFFECTS
8. FOCUSING OUR thought
10. VALUES
11. 1. THE VALUE OF VALUES
12. 1. THE VALUE OF VALUES 2. THE OBJECT OF OBJECTS
13. 1. THE VALUE OF VALUES 2. THE OBJECT OF OBJECTS 3. EVERYTHING IN ITS PLACE
14. 1. THE VALUE OF VALUES
15. @interface Object.new
16. STDLIB?!
17. $ grep -e "^class " stdlib.swift | wc -l 1
18. $ grep -e "^struct " stdlib.swift | wc -l 78 $ grep -e "^enum " stdlib.swift | wc -l 8
19. “VALUE TYPES”
20. “VALUE TYPES” COPIED ON ASSIGNMENT SINGLE OWNER
21. INT, FLOAT, BOOL, ETC. var a = 10 var b = a // a = 10; b = 10 b = 5 // a = 10; b = 5
22. STRING, ARRAY, DICTIONARY var a = [1, 2, 3] var b = a // a = [1, 2, 3]; b = [1, 2, 3] b.append(4) // a = [1, 2, 3]; b = [1, 2, 3, 4]
23. STRUCTS, ENUMS, TUPLES var a = CGSize(width: 5, height: 5) var b = a // a = 5x5; b = 5x5 b.width = 10 // a = 5x5; b = 5x10
24. “REFERENCE TYPES” SHARED ON ASSIGNMENT MULTIPLE OWNERS
25. OBJECTS var a = UIView() var b = a // a.alpha = 1; b.alpha = 1 b.alpha = 0 // a.alpha = 0; b.alpha = 0
26. INTUITION: OBJECTS ARE LIKE OBJECTS
27. INTUITION: VALUES ARE LIKE DATA
28. VALUES ARE SIMPLER
29. extension CGPoint { func distanceTo(_ point: CGPoint) { let dx = self.x - point.x let dy = self.y - point.y return sqrt(dx * dx + dy * dy) } }
30. struct Drawing { var actions: [DrawingAction] } struct DrawingAction { var samples: [TouchSample] var tool: Tool enum Tool { case Pencil(color: UIColor) case Eraser(width: CGFloat) } } struct TouchSample { var location: CGPoint var timestamp: NSTimeInterval }
31. SWIFT <3 VALUES
32. THE 3 I'S 1. INERT 2. ISOLATED 3. INTERCHANGEABLE
33. 1. INERT
34. class MyView { var numberOfBloops: Int { didSet { UIView.animateWithDuration(1, animations: { center.x = numberOfBloops * 10 }, completion: { _ in center.x = 0 }) } } }
35. 2. ISOLATED
36. class User { ... } class ViewController { var user: User } class NetworkOperation { init(user: User) }
37. 3. INTERCHANGEABLE
38. EVER TRIED MAKING A UITouch?
39. YOU CAN'T MOVE YOUR BOUNDARIES
40. struct Drawing { var actions: [DrawingAction] } struct DrawingAction { var samples: [TouchSample] var tool: Tool enum Tool { case Pencil(color: UIColor) case Eraser(width: CGFloat) } } struct TouchSample { var location: CGPoint var timestamp: NSTimeInterval }
41. func renderDrawing(drawing: Drawing) -> UIImage
42. extension TouchSample { static func projectNextTouchSample (fromSamples: [TouchSample]) -> TouchSample }
43. let drawing = ... let projectedSample = projectNextTouchSample(drawing.actions.last!.samples) var projectedDrawing = drawing projectedDrawing.actions.last!.append(projectedSample) renderDrawing(projectedDrawing)
44. MOCKING
45. THE 3 I'S 1. INERT 2. ISOLATED 3. INTERCHANGEABLE
46. *
47. * struct Hmmmm { let someData: Int let aView: UIView }
48. 1. THE VALUE OF VALUES 2. THE OBJECT OF OBJECTS 3. EVERYTHING IN ITS PLACE
49. 2. THE OBJECT OF OBJECTS
50. OBJECTS BEHAVE AND RESPOND
51. BUT VALUES ARE DEAD
53. MANY DEAD VALUES CAN MAKE ONE LIVING IDENTITY
54. class CanvasController { var currentDrawing: Drawing /* ... */ } struct Drawing { /* ... */ }
55. STATE: AN IDENTITY'S VALUE AT SOME TIME
56. VALUE: INERT DATA (DRAWING) IDENTITY: VALUES RELATED IN TIME (DRAWING) > (DRAWING) > (DRAWING) > (DRAWING) STATE: AN IDENTITY'S VALUE AT SOME TIME (DRAWING) > (DRAWING) > (DRAWING) > (DRAWING)
57. SO, OBJECTS
58. OBJECTS REPRESENT IDENTITY MANAGE STATE TRANSITIONS PERFORM SIDE EFFECTS
59. class CanvasController { var currentDrawing: Drawing func handleTouch(touch: UITouch) { currentDrawing = ... } }
60. 1. THE VALUE OF VALUES 2. THE OBJECT OF OBJECTS 3. EVERYTHING IN ITS PLACE
61. 3. EVERYTHING IN ITS PLACE
62. OBJECT LAYER VALUE LAYER
63. OBJECT LAYER VALUE LAYER
64. WHY SEPARATE?
65. “SEPARATE LOGIC FROM ACTION”
66. THE VALUE GAME
67. THE VALUE GAME MAXIMIZE THE VALUE LAYER
68. 1. Incorporate touch into Drawing
69. 1. Incorporate touch into Drawing 2. Estimate touch velocity
70. 1. Incorporate touch into Drawing 2. Estimate touch velocity 3. Smooth touch sample curves
71. 1. Incorporate touch into Drawing 2. Estimate touch velocity 3. Smooth touch sample curves 4. Compute stroke geometry
72. 1. Incorporate touch into Drawing 2. Estimate touch velocity 3. Smooth touch sample curves 4. Compute stroke geometry 5. Render stroke
73. UIVIEW!
74. UIVIEW! MEHHH
75. extension TouchSample { static func estimateVelocities(samples: [TouchSample]) -> [CGPoint] } 1. Incorporate touch into Drawing 2. Estimate touch velocity 3. Smooth touch sample curves 4. Compute stroke geometry 5. Render stroke
76. extension TouchSample { static func smoothTouchSamples(samples: [TouchSample]) -> [TouchSample] } 1. Incorporate touch into Drawing 2. Estimate touch velocity 3. Smooth touch sample curves 4. Compute stroke geometry 5. Render stroke
77. struct PencilBrush { func pathForDrawingAction(action: DrawingAction) -> UIBezierPath } 1. Incorporate touch into Drawing 2. Estimate touch velocity 3. Smooth touch sample curves 4. Compute stroke geometry 5. Render stroke
78. extension Drawing { mutating func appendTouchSample(sample: TouchSample) } 1. Incorporate touch into Drawing (+ update state) 2. Estimate touch velocity 3. Smooth touch sample curves 4. Compute stroke geometry 5. Render stroke
79. OBJECT LAYER VALUE LAYER
80. FUNCTIONAL CORE IMPERATIVE SHELL
81. 1. THE VALUE OF VALUES 2. THE OBJECT OF OBJECTS 3. EVERYTHING IN ITS PLACE
82. SO
83. FOCUSING OUR CONTROL FLOW
84. FOCUSING OUR DEPENDENCIES
85. FOCUSING OUR EFFECTS
86. OBJECT LAYER VALUE LAYER
87. FURTHER READING ▸ Boundaries — Gary Bernhardt ▸ Are We There Yet? — Rich Hickey ▸ SICP — Abelson & Sussman ▸ Enemy of the State — Justin Spahr-Summers
88. Thanks.
89. ‽ ANDYMATUSCHAK.ORG @ANDY_MATUSCHAK