SwiftWro 1: Laziness in Swift

Slides from the talk I gave at the first SwiftWro meetup on 2014-08-20 in Wrocław, Poland.

https://github.com/narfdotpl/swiftwro-1-laziness-in-swift
http://www.swiftwro.com/

Transcript

1. Laziness(in(Swi+ Maciej'Konieczny narf.pl'2'macoscope.com
2. narf.pl
4. Swi$Warsaw.com
5. Python'!
6. Django'!
7. JavaScript*!
8. CoffeeScript+!
9. Objec&ve(C*!
10. Swi$%!
12. Python'!
13. Laziness(in(Swi+
16. delaying)computa0on un0l)necessary
17. never%necessary never%computed
18. poten&al)for removing needless)computa&on
19. poten&al)for reducing memory)footprint
20. poten&al)for infinite data)structures
21. Laziness(allows(the(expression( of(programs(that(would( otherwise(not(terminate
22. not$one$pa(ern
23. Swi$
24. lazy var
25. SequenceType
26. @autoclosure
27. lazy var
28. class BlogPost { var filename: String init(filename: String) { self.filename = filename } }
29. class BlogPost { var filename: String var foo = Foo() init(filename: String) { self.filename = filename } }
30. class BlogPost { var filename: String lazy var foo = Foo() init(filename: String) { self.filename = filename } }
31. class BlogPost { var filename: String init(filename: String) { self.filename = filename } }
32. class BlogPost { var filename: String lazy var markdown: String = { markdownForFile(self.filename) }() init(filename: String) { self.filename = filename } }
33. Swift.nil != ObjC.nil
34. - (NSString *)markdown { if (!_markdown) { _markdown = markdownForFile(self.filename); } return _markdown; }
35. SequenceType
36. for x in xs { // ... }
37. for x in xs { // ... } var _g = xs.generate() while let x = _g.next() { // ... }
38. class Integers: SequenceType { func generate() -> GeneratorOf<Int> { var n = -1 return GeneratorOf { ++n } } }
39. class Integers: SequenceType { func generate() -> GeneratorOf<Int> { var n = -1 return GeneratorOf { ++n } } } for i in Integers() { println(i) // 0, 1, 2, 3, ... }
40. var integers = lazy(Integers())
41. var integers = lazy(Integers()) integers.filter integers.map
42. extension LazySequence { var first: LazySequence.Generator.Element? { for x in self { return x } return nil } } integers.first! // 0
43. var x = integers
44. var x = integers \ .filter { $0 % 2 == 1 } \
45. var x = integers \ .filter { $0 % 2 == 1 } \ .map { $0 * $0 }
46. var x = integers \ .filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 100 } \
47. var x = integers \ .filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 100 } \ .first!
48. var x = integers \ .filter { $0 % 2 == 1 } \ .map { $0 * $0 } \ .filter { $0 > 100 } \ .first! println(x) // 121
49. var x = integers.filter { return $0 % 2 == 1 }.map { return $0 * $0 }.filter { return $0 > 10 }.first! println(x) // 25
50. var x = integers.filter { println("\n\($0)") println("even?") return $0 % 2 == 1 }.map { println("square") return $0 * $0 }.filter { println("threshold") return $0 > 10 }.first! println(x) // 25
51. integers.filter { $0 % 2 == 1 } \ .map { $0 * $0 } .filter { $0 > 10 } \ .first! 0 even? 1 even? square threshold 2 even? 3 even? square threshold 4 even? 5 even? square threshold
52. @autoclosure
53. // without @autoclosure: f({ x }) // with @autoclosure: f(x)
54. func foo(bar: () -> ()) { bar() } foo({ println("baz") })
55. func foo(bar: @autoclosure () -> ()) { bar() } foo(println("baz"))
56. while&not&x&/&un-l&x&/&dopóki&x
57. func dopóki(condition: @autoclosure () -> Bool, body: () -> ()) { if !condition() { body() dopóki(condition(), body) } } var i = 3 dopóki (i == 0) { println(i) i -= 1 }
58. BTW:%compiler%performs tail%call%op2misa2on
59. 㿃
60. not$one$pa(ern
61. removing needless,computa2on
62. reducing memory,footprint
63. expressiveness
64. lazy var foo = Foo()
65. lazy var markdown: String = { markdownForFile(self.filename) }()
66. for x in xs { // ... } var _g = xs.generate() while let x = _g.next() { // ... }
67. // without @autoclosure: f({ x }) // with @autoclosure: f(x)
68. That's'all'folks!
69. narf.pl
71. 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/
72. 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
73. Ques%ons?