© Maciej Konieczny http://narf.pl/ github.com/narfdotpl/swiftwro-1-laziness-in-swift Talk that Macoscope's own Maciej Konieczny gave at the first SwiftWro meetup on 2014-08-20 in Wrocław, Poland. http://vimeo.com/104053958

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

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?