Type Your Business @ ScalaIO, October 2018

This talk was presented at ScalaIO in Lyon, France

Transcript

1. October 2018 @omervk 1
2. § To err is human § Typos § Bugs § Regressions @omervk 2 WORKS ON MY MACHINE
3. @omervk 3 Software Engineering Economics, Barry Boehm, 1981 Logarithmic Scale! 1981
4. § Find Problems Early § Refactor with Confidence § Document Usage @omervk 4
5. § More Code to Write § And Review § And Maintain § So much code @omervk 5
6. § More Code to Write § And Review § And Maintain § So much code § Exhaustive? § 100% coverage is a lie @omervk 6
7. § More Code to Write § And Review § And Maintain § So much code § Exhaustive? § 100% coverage is a lie § Tests are poor documentation @omervk 7
8. § Documentation /** * Connects a cat to all vet clinics * @param catId the id of the cat * @return the number of clinics connected */ @omervk 8
9. § Documentation § Code /** * Connects a cat to all vet clinics * @param catId the id of the cat * @return the number of clinics connected */ def connect(catId: Int, clinicId: Int): Boolean @omervk 9
10. § Documentation § Code § Tests /** * Connects a cat to all vet clinics * @param catId the id of the cat * @return the number of clinics connected */ def connect(catId: Int, clinicId: Int): Boolean test("Cat may not be associated with more than one clinic") @omervk 10
11. § Documentation § Code § Tests § Exceptions?! § And this is a good specimen! /** * Connects a cat to all vet clinics * @param catId the id of the cat * @return the number of clinics connected */ def connect(catId: Int, clinicId: Int): Boolean test("Cat may not be associated with more than one clinic") @omervk 11
12. § We had compile-time annotations § Enforce invariant business rules § Replace the basic, repetitive validation tests and docs @omervk 12
13. § Impact our code’s users § Discover failures early § Understand where validations happen @omervk 13
14. TYPES
15. final case class Connection(host: Any, port: Any) @omervk 15
16. § The Product Development Triathlon by Kent Beck @omervk 16
17. § Like, what even is a host, man? @omervk 17
18. § GOTTA GO FAST @omervk 18
19. § Growing Teams § Refactoring Pains § Shaky Foundations @omervk 19
20. final case class Connection(host: Any, port: Any) @omervk 20
21. Any @omervk 21 Future
22. Any AnyVal @omervk 22 Future -2.0
23. Any AnyVal Int @omervk 23 -2.0 Future 2
24. final case class Connection(host: String, port: Int) @omervk 24
25. /** * @param host the host, denoted as an IPv4 number, defined in * RFC-791 (https://tools.ietf.org/html/rfc791) * @param port the port, a 16-bit unsigned integer * @throws IllegalArgumentException host is not valid * @throws IllegalArgumentException port is not valid */ final case class Connection(host: String, port: Int) @omervk 25
26. Any AnyVal Int ? @omervk 26 -2.0 Future -2 80
27. type Port = Int Refined Interval.Closed[W.`0`.T, W.`65535`.T] final case class Connection(host: String Refined IPv4, port: Port) @omervk 27
28. type Port = Int Refined Interval.Closed[W.`0`.T, W.`65535`.T] final case class Connection(host: String Refined IPv4, port: Port) Connection("not a host", -1) // Fails to compile Connection("127.0.0.1", 8080) // Compiles fine @omervk 28
29. val port: Either[String, Port] = refineV(intMaybePort) § Know what failed § Know why it failed § Proactive, not reactive @omervk 29
30. § fthomas/refined § Type-level combinable predicates § List[Int] Refined (NonEmpty And Forall[Positive]) § Not, And, Or, Xor, Nand, Nor, AllOf, AnyOf, OneOf § Ecosystem @omervk 30
31. § Generic: Equal § Boolean: True, False § Char: Digit, Letter, LetterOrDigit, LowerCase, UpperCase, Whitespace § Numeric: Less, LessEqual, Greater, GreaterEqual, Positive, NonPositive, Negative, NonNegative, Interval, Modulo, Divisible, NonDivisible, Even, Odd § String: EndsWith, IPv4, IPv6, MatchesRegex, Regex, StartsWith, Uri, Url, Uuid, ValidByte, ValidShort, ValidInt, ValidLong, ValidFloat, ValidDouble, ValidBigInt, ValidBigDecimal, Xml, XPath, Trimmed, HexStringSpec § Collection: Contains, Count, Empty, NonEmpty, Forall, Exists, Head, Index, Init, Last, Tail, Size, MinSize, MaxSize @omervk 31
32. § Run-time exceptions à Compile-time errors § Obligate callers explicitly § Document preconditions § Less code § Automated using compiler & macros @omervk 32
33. @omervk 33
34. class WaggingTail(dog: Dog) class Dog def pet(dog: Dog): WaggingTail @omervk 34
35. class WaggingTail(dog: Dog) class Dog def pet(dog: Dog): WaggingTail = { new WaggingTail(otherDog) } @omervk 35
36. class Dog { class WaggingTail { } } @omervk 36
37. class Dog { class WaggingTail { } } def pet(dog: Dog) = { new Dog.WaggingTail } @omervk 37
38. class Dog { class WaggingTail { } } def pet(dog: Dog): dog.WaggingTail = { new dog.WaggingTail } dog == pet(dog).dog // Guaranteed! @omervk 38
39. @omervk 39
40. § IO Barriers § Network § Database § File system § OS § Solution: § Use better abstractions (libraries) § Integration Tests @omervk 40
41. Types Validations § “port is a valid port number” § “the tail we got was the one of the dog we petted” Tests Complex Business Rules § “when a dog has already been petted by another user, wag the tail twice as hard” @omervk 41
42. @omervk 42
43. petDog(dog.id) petDog(cat.id) // this throws BiteException :( @omervk 43
44. § test("Cats should not be petted like dogs") § Too late @omervk 44
45. final case class DogId(id: Int) extends AnyVal final case class Dog(id: DogId, /*...*/) extends Animal def petDog(id: DogId): Unit petDog(cat.id) @omervk 45
46. def sendMeYourId(id: Int) sendMeYourId(dogId) But a DogId is an Int! @omervk 46
47. def sendMeYourId(id: Int) sendMeYourId(dogId.id) @omervk 47
48. § Cumbersome § Implicits? @omervk 48
49. implicit def extractId(id: DogId): Int = id.id @omervk 49
50. implicit def extractId(id: DogId): Int = id.id implicit def extractId(id: ParrotId): Int = id.id implicit def extractId(id: CapybaraId): Int = id.id implicit def extractId(id: CatId): Int = id.id implicit def extractId(id: ScalazId): Int = id.id Ugh. @omervk 50
51. CatId(10) So we change to: final case class CatId private (id: Int) extends AnyVal @omervk 51
52. cat.copy(id = dogId.id) @omervk 52
53. sealed abstract case class CatId (id: Int) extends AnyVal @omervk 53
54. sealed abstract case class CatId (id: Int) extends AnyVal object CatId { private[persistence] def apply(id: Int): CatId = new CatId(id) {} } @omervk 54
55. sealed abstract case class CatId (id: Int) extends AnyVal object CatId { private[persistence] def apply(id: Int): CatId = { // Business logic… new CatId(id) {} } } @omervk 55
56. sealed abstract case class CatId (id: Int) extends AnyVal object CatId { private[persistence] def apply(id: Int): CatId = { // Business logic… new CatId(id) {} } } @omervk Illegal inheritance from value class CatId 56
57. trait DogId val id: Int with DogId = 10.asInstanceOf[Int with DogId] def query(id: Int with DogId): Dog @omervk 57
58. § Int with DogId is an Int § Zero runtime overhead § Accidents less likely @omervk 58
59. § Convention: Int @@ DogId § Don’t roll your own: § shapeless § Scalaz § etc. @omervk 59
60. @newtype case class DogId(id: Int) @omervk 60
61. type DogId = DogId.Type object DogId { type Repr = Int type Base = Any { type DogId$newtype } trait Tag extends Any type Type <: Base with Tag def apply(id: Int): DogId = id.asInstanceOf[DogId] implicit final class Ops$newtype(val $this$: Type) extends AnyVal { def id: Int = $this$.asInstanceOf[Int] } } @omervk 61
62. § Macro § Looks like a case class § Actually tags § Zero-cost wrapper § estatico/scala-newtype § Opaque Types (SIP-35) @newtype case class DogId(id: Int) @omervk 62
63. @newtype case class DogId(id: Int) def sendMeYourId(id: Int) sendMeYourId(dogId) @omervk 63
64. @newsubtype case class DogId(id: Int) § Now DogId extends Int @omervk 64
65. @newsubtype class DogId(id: Int) object DogId { private[persistence] def apply(id: Int): DogId = { // Business logic here... id.asInstanceOf[DogId] } } @omervk 65
66. @newsubtype class DogId(id: Int) object DogId { private[persistence] def apply(id: Int): DogId = { // Business logic here... id.asInstanceOf[DogId] } } val dogId: DogId = DogId(10) val unwrapped: Int = dogId @omervk 66
67. @omervk 67
68. query(catId) delete(catId) update(Cat(catId, ...)) @omervk 68
69. query(catId) delete(catId) update(Cat(catId, ...)) create(Cat(???, ...)) § Wait, what even is an id? § Ids are implementation detail @omervk 69
70. final case class DogWithId(id: DogId, entity: Dog) def query(id: DogId): DogWithId def update(entity: DogWithId): DogWithId def create(entity: Dog): DogWithId @omervk 70
71. final case class With[Entity, Id](id: Id, entity: Entity) def query(id: Id): With[Entity, Id] def update(entity: With[Entity, Id]): With[Entity, Id] def create(entity: Entity): With[Entity, Id] @omervk 71
72. final case class With[Entity, Id](id: Id, entity: Entity) def query(id: Id): Entity With Id def update(entity: Entity With Id): Entity With Id def create(entity: Entity): Entity With Id @omervk 72
73. final case class With[Entity, Id](id: Id, entity: Entity) abstract class Repository[Entity, Id] { def query(id: Id): Entity With Id def update(entity: Entity With Id): Entity With Id def create(entity: Entity): Entity With Id } More: https://www.iravid.com/posts/slick-and-shapeless.html @omervk 73
74. § Repository[Dog, CatId] § Typed connection between DogId and Dog? § DogId Represents Dog @omervk 74
75. final case class With[Entity, Id](id: Id, entity: Entity) abstract class Repository[Entity, Id] { def query(id: Id): Entity With Id def update(entity: Entity With Id): Entity With Id def create(entity: Entity): Entity With Id } @omervk 75
76. final case class With[Entity, Id](id: Id, entity: Entity) abstract class Repository[Entity, Id] { def query(id: Id): Entity With Id def update(entity: Entity With Id): Entity With Id def create(entity: Entity): Entity With Id } trait Represents[Identifier, Entity] @omervk 76
77. final case class With[Entity, Id](id: Id, entity: Entity) (implicit ev: Id Represents Entity) abstract class Repository[Entity, Id](implicit ev: Id Represents Entity) { def query(id: Id): Entity With Id def update(entity: Entity With Id): Entity With Id def create(entity: Entity): Entity With Id } trait Represents[Identifier, Entity] @omervk 77
78. implicit val idOfDog: DogId Represents Dog = ... § Won’t compile: § new Repository[Dog, CatId] {} § new Repository[Cat, DogId] {} § new Repository[Dog, DogId] {}.query(catId) @omervk 78
79. @newsubtype class DogId(a: Int) object DogId { private[persistence] def apply(a: Int): DogId = { // Business logic here... a.asInstanceOf[DogId] } } final case class Dog(/*...*/) object Dog { implicit val idOfDog: DogId Represents Dog = new DogId Represents Dog { } } final class DogRepository extends Repository[Dog, DogId] @omervk 79
80. @omervk 80
81. § Path-Dependent Types § Self-Recursive / F-bound Types § Product and Sum Types § Structural Types § Type Members § Kinds § Variance § Existential Types* @omervk 81 Photo Opportunity
82. § -Xfatal-warnings § Linter § -Xlint § WartRemover § Scalafix § Your IDE § See: Power Up Your Build @omervk 82
83. § Increase robustness § Fail-fast § Replace some tests and documentation § Where can your code benefit? @omervk 83
84. @omervk 84