[Combine 책 정리] Chapter 13: Resource Management

안녕하세요 코찐입니다.

아래의 자료를 따라서 공부하고 있습니다.

https://www.raywenderlich.com/books/combine-asynchronous-programming-with-swift/v2.0

 

리소스 관리하는 Publisher 들인데, API 작업할 때 유용하게 사용할 수 있습니다.

share

value 타입이 아닌 reference 타입의 publisher를 공유할 수 있도록 해줍니다.

주의할 점은 이미 complete 된 share publisher를 구독하면 complete만 받게 됩니다.

let shared = URLSession.shared
  .dataTaskPublisher(for: URL(string: "https://www.raywenderlich.com")!)
  .map(\.data)
  .print("shared")
  .share()

print("subscribing first")

let subscription1 = shared.sink(
  receiveCompletion: { _ in },
  receiveValue: { print("subscription1 received: '\($0)'") }
)

print("subscribing second")

let subscription2 = shared.sink(
  receiveCompletion: { _ in },
  receiveValue: { print("subscription2 received: '\($0)'") }
)

subscribing first
shared: receive subscription: (DataTaskPublisher)
shared: request unlimited
subscribing second
shared: receive value: (275400 bytes)
subscription1 received: '275400 bytes'
subscription2 received: '275400 bytes'
shared: receive finished

 

multicast

connect()를 호출해야 이벤트를 시작합니다.

그래서 subscription을 다 만들어두고, connect 할 수 있어서 편합니다.

let subject = PassthroughSubject<Data, URLError>()

let multicasted = URLSession.shared
    .dataTaskPublisher(for: URL(string: "https://www.raywenderlich.com")!)
    .map(\.data)
    .print("multicast")
    .multicast(subject: subject)

// 3
let subscription1 = multicasted
    .sink(
        receiveCompletion: { _ in },
        receiveValue: { print("subscription1 received: '\($0)'") }
    )

let subscription2 = multicasted
    .sink(
        receiveCompletion: { _ in },
        receiveValue: { print("subscription2 received: '\($0)'") }
    )

let cancellable = multicasted.connect()

multicast: receive subscription: (DataTaskPublisher)
multicast: request unlimited
multicast: receive value: (275400 bytes)
subscription1 received: '275400 bytes'
subscription2 received: '275400 bytes'
multicast: receive finished

 

future

future는 클로저 안의 동작을 즉시 실행합니다.

그리고 구독하면 그 값을 전달합니다.

 

func performSomeWork() throws -> Int {
    print("Performing some work and returning a result")
    return 5
}

let future = Future<Int, Error> { fulfill in
    do {
        let result = try performSomeWork()
        fulfill(.success(result))
    } catch {
        fulfill(.failure(error))
    }
}

print("Subscribing to future...")

let subscription1 = future
    .sink(
        receiveCompletion: { _ in print("subscription1 completed") },
        receiveValue: { print("subscription1 received: '\($0)'") }
    )

let subscription2 = future
    .sink(
        receiveCompletion: { _ in print("subscription2 completed") },
        receiveValue: { print("subscription2 received: '\($0)'") }
    )

Performing some work and returning a result
Subscribing to future...
subscription1 received: '5'
subscription1 completed
subscription2 received: '5'
subscription2 completed