1.
Functional Core
Reactive Shell
YOW! West 2016
@mokagio

2.
Spaghetti

3.
Spaghetti Architecture

4.
Lasagna

5.
Lasagna Architecture

6.
Ravioli

7.
Ravioli Architecture

8.
Pizza

9.
Back to the
lasagna...

10.
Consumer POV

11.
Unit Tests POV

12.
Dependencies Tree

13.
Side Effects

14.
Stubs & Mocks

15.
Stub
Test Double
Indirect Inputs

16.
Use a stub for the dependencies

17.
Mock
Test Double
Indirect Outputs

18.
Use a mock to verify a side effect

19.
Is this a good
idea?

20.
Mocks Tell Lies

21.
Not
Production
Code
!

22.
func sum(a: Int, b: Int) ->
Int

23.
mock(+)
or
expect(sum(1, 2)) == 3

24.
Ken Scambler
"To Kill a Mockingtest"
"Mocks & Stubs"

25.
Many Dependencies
&
Side Effects

26.
Gary Bernhardt
Boundaries

27.
Objects >> Values

28.
func sum(a: Int, b: Int) ->
Int

29.
Pure Function

30.
But I do need I/O...

31.
Decision
vs
Action

32.
Example
Insert object in DB if
<condition>

33.
Standard Approach
class DatabaseService {
func insertObjects(objects: [DBObject], updatedAfter date: NSDate) {
// 1. Filter objects array based on criteria
// 2. For each remainig object
// 2.1 Insert object in DB
}
}

34.
Split Approach: Decision
struct DBAction {
enum Mode {
case Insert
case Update
case Delete
}
let objects: [DBObject]
let mode: Mode
}
func persistObjectsAction(objects: [DBObject], updatedAfter updatedDate: NSDate) ->
// 1. Filter object based on date
// 2. Create action value using objects and insert mode
}

35.
Split Approach: Decision
Easy to test using in memory values
No DB setup needed
Really does only one thing

36.
Split Approach: Action
class DatabaseService {
func performAction(action: DBAction) {
// for each object switch on mode and perform mode action
}
}

37.
Split Approach: Action
Testable using simple scenarios
"Once and for all"

38.
Toppings

39.
Functional Core
Imperative Shell
Gary Bernhardt

40.
Functional Core, Imperative Shell

41.
Pizza!

42.
Functional Core
Imperative Shell
Reactive Shell

43.
Functional Core, Reactive Shell

44.
Example
App fetching stuff from
network and cache

45.
Functional Core
struct Stuff {
let id: String
let text: String
let number: Int
}
extension Stuff {
init?(json: [String: AnyObject]) { /* ... */ }
}
extension Stuff {
init(realmObject: RealmStuff) { /* ... */ }
}

46.
Functional Core
describe("Stuff from JSON dictionary") {
context("when the dictionary contains all the valid keys") {
it("it returns an instance configured with the values in the dictionary") {
let anyId = "any id"
let anyText = "any text"
let anyNumber = 42
let dict: [String: AnyObject] = ["id": anyId, "text": anyText, "number": anyNum
let stuff = Stuff(json: dict)
expect(stuff?.id) == anyId
expect(stuff?.text) == anyText
expect(stuff?.number) == anyNumber
}
}
}
describe("Stuff model from Realm object") {
it("sets its properties based on the Realm object one") {
let realmObject = RealmStuff.test_fixture()
let sut = Stuff(realmObject: realmObject)
expect(sut.id) == realmObject.id
expect(sut.number) == realmObject.number
expect(sut.text) == realmObject.text
}
}

47.
Functional Core
extension CellViewModel {
init(stuff: Stuff) {
self.text = "(stuff.id) - (stuff.text) ((stuff.number))"
}
}
describe("CellViewModel") {
context("when initialized with a Stuff model") {
it("sets the text using the stuff properties") {
let stuff = Stuff(id: "123", text: "any text", number: 42)
let sut = CellViewModel(stuff: stuff)
expect(sut.text) == "123 - any text (42)"
}
}
}

48.
Side Effect Code
class ViewController: UIViewController {
enum Effect {
case UpdateView(viewModels: [CellViewModel])
case PresentAlert(error: ErrorType)
}
func performEffect(effect: Effect) {
switch effect {
case .UpdateView(let viewModels):
self.viewModels = viewModels
tableView.reloadData()
case .PresentAlert(let error):
presentErrorAlert(error)
}
}
}

49.
Reactive Shell
merge([
databaseService.allStuff()
.map { $0.map { Stuff(realmObject: $0) } },
networkService.performRequest(toEndpoint: .GetStuff)
.flatMapLatest { JSON in
return Stuff.stuffProducer(withJSON: JSON)
}
])
.map { stuffArray in stuffArray.map { CellViewModel(stuff: $0) } }
.map { viewModels in Effect.UpdateView(viewModels: viewModels) }
.observeOnMainThread()
.on(
failed: { [weak self] error in
self?.performEffect(Effect.PresentAlert(error: error))
},
next: { [weak self] effect in
self?.performEffect(effect)
}
)
.start()

50.
Good Idea?

51.
Cons
Learning curve
Long and awkward reactive shell

52.
Pros
Reactive shell tells the story
Higher code mobility
Learning is GOOD

53.
Gio
@mokagio
http://mokacoding.com