Transforming Elements

toArray

• Sequence의 element를 array의 element로 변환한다.

Observable.of(1, 2, 3, 4, 5)
.toArray()
.subscribe {
    print("🟢", $0)
}

map

Observable.from(1...5)
.map { $0 * 10 }
.subscribe {
    print("🟢", $0)
}

enumerated

• 방출된 element의 index와 value를 포함하는 tuple을 방출하도록 한다.

Observable.from(1...5)
.enumerated()
.subscribe {
    print("🟢", $0)
}

Transforming Observables

• 🌟 Upstream에서 .error가 발생한다면, 생성된 Observable은 dispose 된다.

flatMap

• Observable에서 방출한 element를 새로운 Observable를 만들며, 만들어진 Observable의 element를 방출한다.
  
  

struct Student {
    let name: String
    let scoreSubject: BehaviorSubject<Int>
}

let student🟢 = Student(
    name: "🟢",
    scoreSubject: BehaviorSubject<Int>(value: 80)
)
let student🔴 = Student(
    name: "🔴",
    scoreSubject: BehaviorSubject<Int>(value: 90)
)
let studentSubject = PublishSubject<Student>()

studentSubject.flatMap { $0.scoreSubject }
    .debug()
    .subscribe()
    .disposed(by: disposeBag)

studentSubject.onNext(student🟢) // 80

student🟢.scoreSubject.onNext(85) // 85

studentSubject.onNext(student🔴) // 90

student🟢.scoreSubject.onNext(95) // 95

student🔴.scoreSubject.onNext(100)  // 100

flatMapFirst

• Observable에서 방출한 element를 새로운 Observable를 만들며, 만들어진 Observable의 element를 방출한다.
• 이전 observable이 완료되어야지만 다음 observable의 element를 받을 수 있다.
  
  

let student🟢 = Student(
    name: "🟢",
    scoreSubject: BehaviorSubject<Int>(value: 80)
)
let student🔴 = Student(
    name: "🔴",
    scoreSubject: BehaviorSubject<Int>(value: 90)
)
let studentSubject = PublishSubject<Student>()

studentSubject.flatMapFirst { $0.scoreSubject.debug($0.name) }
.debug("flatMapFirst")
.subscribe()
.disposed(by: disposeBag)

studentSubject.onNext(student🟢) // 80

student🟢.scoreSubject.onNext(85) // 85

studentSubject.onNext(student🔴) // 🌟 이전 observable(`student🟢`)이 완료되어야지만 다음 observable(student🔴)의 것을 방출한다.
student🔴.scoreSubject.onNext(100)

student🟢.scoreSubject.onNext(95) // 95

student🟢.scoreSubject.onCompleted()
studentSubject.onNext(student🔴) // 100

student🔴.scoreSubject.onNext(70)  // 70

flatMapLatest

• Observable에서 방출한 element를 새로운 Observable를 만들며, 만들어진 Observable의 element를 방출한다.
• 새로이 발행된 element가 전달되면, 이전 Observable은 dispose하고 새로운 Observable을 만들고 element를 방출한다.
  • 이전 observable이 dipose된다. 다음 observable의 값만 방출한다.
    
    

let student🟢 = Student(
    name: "🟢",
    scoreSubject: BehaviorSubject<Int>(value: 80)
)
let student🔴 = Student(
    name: "🔴",
    scoreSubject: BehaviorSubject<Int>(value: 90)
)
let studentSubject = PublishSubject<Student>()

studentSubject.flatMapLatest { $0.scoreSubject.debug($0.name) }
    .debug("flatMapLatest")
    .subscribe()
    .disposed(by: disposeBag)

studentSubject.onNext(student🟢) // 80

student🟢.scoreSubject.onNext(85) // 85

studentSubject.onNext(student🔴) // 90, 🌟 이전 observable(`student🟢`)이 dipose된다.

student🟢.scoreSubject.onNext(95) // 마지막 observable인 `student🔴`의 값만 방출된다.

student🔴.scoreSubject.onNext(100)  // 100

Observing Events

materialize

• Observable<Int> → Observable<Event<Value>>

dematerialize

• Observable<Event<Value>> → Observable<Int>

let disposeBag = DisposeBag()
struct Student {
    let name: String
    let scoreSubject: BehaviorSubject<Int>
}

let student🟢 = Student(
    name: "🟢",
    scoreSubject: BehaviorSubject<Int>(value: 1)
)
let student🔴 = Student(
    name: "🔴",
    scoreSubject: BehaviorSubject<Int>(value: 10)
)
let studentSubject = PublishSubject<Student>()

let materialized = studentSubject
    .flatMapLatest {
        $0.scoreSubject.materialize().debug($0.name)
    }
materialized
    .debug("materialized")
    .subscribe()
    .disposed(by: disposeBag)

materialized
    .dematerialize()
    .debug("dematerialized")
    .subscribe()
    .disposed(by: disposeBag)

studentSubject.on(.next(student🟢))
student🟢.scoreSubject.on(.next(2))
student🟢.scoreSubject.on(.error(CustomError.error))
studentSubject.on(.next(student🔴))
student🟢.scoreSubject.on(.next(3))
student🔴.scoreSubject.on(.next(20))