Swift Warsaw 2: Laziness in Swift

Slides from the talk I gave at the second Swift Warsaw meetup on 2014-08-28 in Warsaw, Poland.

https://github.com/narfdotpl/swift-warsaw-2-laziness-in-swift
http://swiftwarsaw.com/

Transcript

1. Laziness(in(Swi+ Maciej'Konieczny narf.pl'2'macoscope.com
2. Python'!
3. Django'!
4. JavaScript*!
5. CoffeeScript+!
6. Objec&ve(C*!
7. Swi$%!
9. Python'!
10. Laziness
12. delaying)computa0on un0l)necessary
13. never%necessary never%computed
14. removing needless computa1on
15. reducing memory footprint
16. infinite data structures
17. Laziness(allows(the(expression( of(programs(that(would( otherwise(not(terminate —"Ma%"Might
18. not$one$pa(ern
19. Swi$
20. lazy var
21. SequenceType
22. @autoclosure
23. lazy var
24. class BlogPost { var filename: String }
25. class BlogPost { var filename: String init(filename: String) { self.filename = filename } }
26. class BlogPost { var filename: String var image = Image() init(filename: String) { self.filename = filename } }
27. class BlogPost { var filename: String lazy var image = Image() init(filename: String) { self.filename = filename } }
28. class BlogPost { var filename: String lazy var image = Image() init(filename: String) { self.filename = filename } } var post = BlogPost(filename: "sw2.md") post.image
29. class BlogPost { var filename: String lazy var image = Image() init(filename: String) { self.filename = filename } }
30. class BlogPost { var filename: String lazy var image = \ Image(forFilename: self.filename) init(filename: String) { self.filename = filename } }
31. class BlogPost { var filename: String lazy var image = { Image(forFilename: self.filename) }() init(filename: String) { self.filename = filename } }
32. Swi$%≠%ObjC
33. nil$≠$nil
34. - (Image *)image { if (!_image) { _image = [[Image alloc] imageForFilename:self.filename]; } return _image; }
35. SequenceType
36. for x in xs { // ... }
37. for x in xs { // ... } var _g = xs.generate() while let x = _g.next() { // ... }
38. awesome
39. class Integers: SequenceType { func generate() -> GeneratorOf<Int> { var n = -1 return GeneratorOf { ++n } } }
40. class Integers: SequenceType { func generate() -> GeneratorOf<Int> { var n = -1 return GeneratorOf { ++n } } } for i in Integers() { println(i) // 0, 1, 2, 3, ... }
41. lazy()
42. lazy() var xs = [1, 2, 3] xs.lazy()
43. lazy() var xs = [1, 2, 3] xs.lazy() LazySequence LazyForwardCollection LazyRandomAccessCollection
44. var integers = lazy(Integers())
45. var integers = lazy(Integers()) integers.filter integers.map
46. var x = integers
47. var x = integers \ .filter { $0 % 2 == 1 }
48. var x = integers \ .filter { $0 % 2 == 1 } \ .map { $0 * $0 }
49. var x = integers \ .filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 100 }
50. var x = integers \ .filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 100 } \ .first!
51. var x = integers \ .filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 100 } \ .first! println(x) // 121
52. call$order
53. var x = integers \ .filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 100 } \ .first! println(x) // 121
54. var x = integers.filter { return $0 % 2 == 1 }.map { return $0 * $0 }.filter { return $0 > 10 }.first! println(x) // 25
55. var x = integers.filter { println("\n\($0)") println("odd?") return $0 % 2 == 1 }.map { println("square") return $0 * $0 }.filter { println("threshold") return $0 > 10 }.first! println(x) // 25
56. integers.filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 10 } \ .first!
57. integers.filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 10 } \ .first! 0
58. integers.filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 10 } \ .first! 0 odd?
59. integers.filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 10 } \ .first! 0 odd? 1
60. integers.filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 10 } \ .first! 0 odd? 1 odd?
61. integers.filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 10 } \ .first! 0 odd? 1 odd? square
62. integers.filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 10 } \ .first! 0 odd? 1 odd? square threshold
63. integers.filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 10 } \ .first! 0 odd? 1 odd? square threshold 2 odd? 3 odd? square threshold 4 odd? 5 odd? square threshold
64. declara've
65. extension LazySequence { var first: LazySequence.Generator.Element? { for x in self { return x } return nil } } integers.first! // 0
66. @autoclosure
67. // without @autoclosure: f({ x })
68. // without @autoclosure: f({ x }) // with @autoclosure: f(x)
69. func f() -> Bool { return true }
70. func f() -> Bool { return true } func g() -> Bool { return false }
71. func f() -> Bool { println("f") return true } func g() -> Bool { println("g") return false }
72. func or
73. func or(left: Bool
74. func or(left: Bool, right: Bool)
75. func or(left: Bool, right: Bool) -> Bool
76. func or(left: Bool, right: Bool) -> Bool { if left { return left }
77. func or(left: Bool, right: Bool) -> Bool { if left { return left } else { return right } }
78. func or(left: Bool, right: Bool) -> Bool { if left { return left } else { return right } }
79. func or(left: Bool, right: Bool) -> Bool { if left { return left } else { return right } } println(or(f(), g())) // f, g, true
80. func or(left: Bool, right: () -> Bool) -> Bool { if left { return left } else { return right() } } println(or(f(), { g() })) // f, true
81. func or(left: Bool, right: @autoclosure () -> Bool) -> Bool { if left { return left } else { return right() } } println(or(f(), g())) // f, true
82. powerful
83. f() || g()
84. f() || { g() }
85. Laziness
86. not$one$pa(ern
87. removing needless computa1on
88. reducing memory footprint
89. infinite data structures
90. expressiveness
91. lazy var image = Image()
92. lazy var image = Image() lazy var image = { Image(forFilename: self.filename) }()
93. for x in xs { // ... }
94. for x in xs { // ... } var _g = xs.generate() while let x = _g.next() { // ... }
95. // without @autoclosure: f({ x })
96. // without @autoclosure: f({ x }) // with @autoclosure: f(x)
97. // without @autoclosure: f({ x }) // with @autoclosure: f(x) POWER!
98. That's'all'folks!
99. narf.pl
100. Ques%ons?
101. References((1(of(2) • Understand)and)implement)laziness,#Ma&#Might h&p:/ /ma&.might.net/ar3cles/implemen3ng7 laziness/ • WWDC)2014,)Session)404:)Advanced)Swi> h&ps:/ /developer.apple.com/videos/wwdc/2014/
102. References((2(of(2) • Lazy%by%name,%lazy%by%nature,#airspeedvelocity h2p:/ /airspeedvelocity.net/2014/07/26/lazy>by> name>lazy>by>nature/ • /r/aww h2p:/ /www.panopCkos.com/r/aww/top