Speaking in Types

Slides for 2015 October 16 talk at CocoaConf

Transcript

1. Speaking in Types How I Learned to Stop Worrying and Love the Type System TJ Usiyan - @griotspeak © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 1
2. How can we examine types? © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 2
3. Examining Types in Xcode • Option click • Look at declarations • Look at the generated header © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 3
4. What is a Type? © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 4
5. What is a Type? The description of a portion of our system's domain. © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 5
6. What is a Type? Types are how we describe the data that our system works with. © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 6
7. In Objective-C, Compiler puts trust in you. In Swift, you put trust in compiler — Yakko Smirnoff I'm Sorry Dave. I'm Afraid I can't do that. © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 7
8. © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 8
9. NSError NSError *error = nil; [myContext save:&error]; if (!error) { /* "Woohoo" */ } else { /* "Oh noes!" */ } © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 9
10. NSError Redux NSError *error = nil; BOOL success = [myContext save:&error]; if (success) { /* "Woohoo" */ } else { /* "Oh noes!" */ } © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 10
11. NSError Re-Redux do { try/*(?|!)?*/ myContext.save() } catch { } © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 11
12. Result enum Result<T> { case Error(NSError) case Success(T) } © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 12
13. "An Either by any other name would compile as sweet." — Gilliam Shakespeare enum Either<T, U> { case Left(T) case Right(U) } © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 13
14. © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 14
15. Make Illegal States Unrepresentable — Yaron Minsky let contactInfo:(PhoneNumber?, EmailAddress?) © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 15
16. enum ContactInfo { case Phone(PhoneNumber) case Email(EmailAddress) case PhoneAndEmail(PhoneNumber, EmailAddress) } © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 16
17. © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 17
18. On Semantics Demo © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 18
19. Enums Are Delightful. enum FileLoadingResult { case Success(NSData) case LoadError(NSError) } © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 19
20. Enums Are Delightful. enum Foo {} © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 20
21. Enums Are Delightful. enum MyNamespace {} © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 21
22. © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 22
23. Optionals Are Quite Nice as Well. typedef NS_ENUM(NSInteger, YouCanGetWith) { YouCanGetWithNull = 0, YouCanGetWithThis, YouCanGetWithThat}; © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 23
24. Optionals Are Quite Nice as Well. typedef NS_ENUM(NSInteger, YouCanGetWith) { YouCanGetWithNull = 0, YouCanGetWithThis, YouCanGetWithThat}; vs enum YouCanGetWith { case This, That } © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 24
25. © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 25
26. Putting the 'Algebra' in Algebraic Data Types © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 26
27. Algebra of Data Types - Zero Type Void /// The empty tuple type. /// /// This is the default return type of /// functions for which no explicit /// return type is specified. typealias Void = () © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 27
28. Algebra of Data Types - Sum Types Enums enum PrimaryColor { case Red, Blue, Yellow } enum Either<T, U> { case Left(T) case Right(U) } let foo:Either<Bool, PrimaryColor> // 2(Bool) + 3(PrimaryColor) possible values © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 28
29. Algebra of Data Types - Product Types Tuples let bar:(Bool, PrimaryColor) // 2(Bool) * 3(PrimaryColor) possible values © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 29
30. © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 30
31. Functions Types Need Love Too. — Samantha Wolf © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 31
32. Functions are Maps! func myRandom() -> Int func consumeNumber(Int) // (Int) -> () func sortNums([Int]) -> [Int] © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 32
33. Function Types func find<C : CollectionType where C.Generator.Element : Equatable> (domain: C, value: C.Generator.Element) -> [C.Generator.Element] vs func find<C : CollectionType where C.Generator.Element : Equatable> (domain: C, value: C.Generator.Element) -> C.Index? vs func find<C : CollectionType where C.Generator.Element : Equatable> (domain: C, value: C.Generator.Element) -> C.Generator.Element © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 33
34. © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 34
35. Optional Initializers …when illegal state is completely worth it struct ScaleDegree { init(diatonicValue:DiatonicValue, chromaticValue:ChromaticValue) init(accidental:Accidental, diatonicValue:DiatonicValue) init?(quality:Interval.Quality, diatonic:DiatonicValue) } let scaleDegree = ScaleDegree(.Perfect, .Fifth)! © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 35
36. Polymorphism! © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 36
37. Parametric Polymorphism struct Array<T> class Thing<T> func foo<T> protocol BazableType { typealias T } © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 37
38. Parametric Polymorphism • Structs • Enums • Classes • Prototypes • Structs • Classes © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 38
39. Trait Polymorphism struct Array<T:Equatable> class Thing<T:Equatable> func foo<T:Equatable> © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 39
40. Trait Polymorphism • Structs • Enums • Classes • Functions © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 40
41. © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 41
42. Generic Function Signatures <T>(T) -> () © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 42
43. Generic Function Signatures <T>([T]) -> [T] © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 43
44. Generic Function Signatures <T: Comparable>([T]) -> [T] © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 44
45. Generic Function Signatures <T, U>(T) -> U © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 45
46. Generic Function Signatures <T>(T, T) -> T © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 46
47. Generic Function Signatures <T,U,V>((U -> V), (T -> U)) -> (T -> V) © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 47
48. Names Are Part of a Type func stride<T : Strideable>(from start: T, to end: T, by stride: T.Stride) -> StrideTo<T> func stride<T : Strideable>(from start: T, through end: T, by stride: T.Stride) -> StrideThrough<T> © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 48
49. Names Are Part of a Type … start: T, to end: … … start: T, through end: … © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 49
50. Function Overloading © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 50
51. Function Overloading +(T, T) -> T © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 51
52. Function Overloading func +(lhs: Float, rhs: Float) -> Float func +<T>(lhs: Int, rhs: UnsafePointer<T>) -> UnsafePointer<T> func +<T>(lhs: UnsafePointer<T>, rhs: Int) -> UnsafePointer<T> func +(lhs: Int, rhs: Int) -> Int func +(lhs: UInt, rhs: UInt) -> UInt func +(lhs: Int64, rhs: Int64) -> Int64 func +(lhs: UInt64, rhs: UInt64) -> UInt64 func +<T>(lhs: Int, rhs: UnsafeMutablePointer<T>) -> UnsafeMutablePointer<T> func +<T>(lhs: UnsafeMutablePointer<T>, rhs: Int) -> UnsafeMutablePointer<T> func +(lhs: Int32, rhs: Int32) -> Int32 func +(lhs: UInt32, rhs: UInt32) -> UInt32 func +(lhs: Int16, rhs: Int16) -> Int16 func +(lhs: UInt16, rhs: UInt16) -> UInt16 func +(lhs: Int8, rhs: Int8) -> Int8 func +(lhs: UInt8, rhs: UInt8) -> UInt8 func +(lhs: Double, rhs: Double) -> Double func +(lhs: String, rhs: String) -> String // `SummableType` anyone? © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 52
53. Higher Kinded Types © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 53
54. Higher Kinded Types func ==<T : Equatable>(lhs: T?, rhs: T?) -> Bool /// Returns true if these arrays contain the same elements. func ==<T : Equatable>(lhs: [T], rhs: [T]) -> Bool /// Returns true if these arrays contain the same elements. func ==<T : Equatable>(lhs: Slice<T>, rhs: Slice<T>) -> Bool /// Returns true if these arrays contain the same elements. func ==<T : Equatable>(lhs: ContiguousArray<T>, rhs: ContiguousArray<T>) -> Bool © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 54
55. Higher Kinded Types How can we state that a container holding an Equatable type is Equatable? © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 55
56. Higher Kinded Types How can we state that a container holding an Equatable type is Equatable? © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 56
57. Higher Kinded Types We must repeat ourselves. This fact is unfortunate. © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 57
58. Higher Kinded Types - Map, Filter, and Friends /// Return an `Array` containing the results of mapping `transform` /// over `source`. func map<S : SequenceType, T>(source: S, transform: (S.Generator.Element) -> T) -> [T] /// Return an `Array` containing the results of mapping `transform` /// over `source`. func map<C : CollectionType, T>(source: C, transform: (C.Generator.Element) -> T) -> [T] © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 58
59. • The type system is our friend • Types can hold more meaning than in Obj-C. © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 59
60. Sources • Effective ML 1 • Algebra of Data Types [^2] 1 https://vimeo.com/14313378 [^2]:http://chris-taylor.github.io/blog/2013/02/10/the-algebra-of-algebraic-data-types/ © Speaking in Types - CocoaConf San Jose - @griotspeak, 2015 60