Swift Optionals and Enums - dotSwift 2015

Opening talk from dotSwift 2015 (dotSwift.io), the first ever Swift conference.
Video available at www.youtube.com/watch?v=DTAs_OVGWIs

"For Dimitri, the announcement of Swift was not a revolution but a revelation. In this opening talk at dotSwift, he explores a few "Swiftisms" like Optionals and Enums."

Transcript

1. Think Swiftly
4. When switching to Swift…
5. Stop thinking Objective-C
6. Start thinking Swift
7. Swiftisms
8. Swift•is•m (swɪftɪzəm) adj. circa 2015 A Swift idiom or pattern showing the safer, compact, and expressive nature of Swift, usually not achievable in Objective-C
9. Optionals
10. Optionals Not love at first sight
11. June 2nd: excited
12. June 3rd : fall in ❤️ with Swift syntax [ ] ; @ & *
13. June 3rd : fall in ❤️ with Swift syntax [ ] ; @ & * For Sale
14. June 4th : Write actual code UILabel? doesn’t have a text property fatal error: unexpectedly found nil while unwrapping an Optional value Value of optional type 'CGFloat?' not unwrapped; did you mean to use '!' or '?'?
15. Solution #1 Hecticly add more ? and!
17. Quantum mechanics
18. Erwin Schrödinger Nobel Prize for Physics (1933)
19. Schrödinger Cat
20. Schrödinger Cat
21. Schrödinger Cat Dead AND Alive
22. Optionals nil AND non-nil
23. Optionals var a:String? var b:String
24. Optionals var cat:Cat? var cat2:Cat
25. Optionals var text = cat.name
26. If let statement if let realCat = cat { // cat is not nil println("Hurray, \(realCat.name) is alive !") } else { // cat is nil println("Sorry, your cat is dead…") }
27. nil coalescing operator var text = cat?.name ?? "RIP"
28. var text = cat?.name
29. Optionals var a:String? • Model a null state • Tell the compiler
 « this could be nil » • Anything else has a value
30. Making your code safer • Eliminates whole class of bugs • nil-related crashes • uninitialized variables • incomplete object initialization • Eliminates useless nil-checks • Forces necessary nil-checks
31. One more thing…
32. Implicitly Unwrapped Optional a.k.a, exclamation mark var a:String!
33. -Dimitri « Trust me, in theory this can never be nil »
34. « In theory, there is no difference between theory and practice.
35. « In theory, there is no difference between theory and practice. In practice, there is »
36. 90% Swift crashes misuse of exclamation mark
37. var text = cat!.name assert(cat != nil, "Cat cannot be nil")
38. ! ? if let New Best Friends
39. Swift Enums
40. One Table View, 4 States Loading Items Book 1 Book 2 Book 3 Book 4 Book 5 Book 6 Book 7 Error Error Occurred Unable to connect to host api.abc.com/v1/example Empty No Item yet Start by adding your first item Add Item NSError [Book]
41. Swift enums enum State { case Loading case Error case Empty case Items } var state:State = .Loading var data:[Book]? var error:NSError?
42. Swift enums enum State { case Loading case Error(NSError) case Empty case Items([Book]) } var state:State = .Loading Enum Associated Values
43. Associated Values switch state { case .Loading: println("Loading") case .Error(let error): println("Error: \(error.localizedDescription)") case .Empty: println("Empty") case .Items(let items): println("They are \(items.count) items in the array") }
44. Enum Associated Values • Associated Values help reduce state • Protects access to data • Enforced by compiler
45. Extra coolness enum State { case Loading case Error(NSError) case Empty case Items([Book]) }
46. Extra coolness enum State<T> { case Loading case Error(NSError) case Empty case Items([T]) } Generics !
47. Extra coolness enum Result<T> { case Error(NSError) case Result(T) } Generic Result Type!
50. 2014 is the new 1984