WWDC 2021: AsyncSequence vs. Combine

Jul 6 2021 · Swift 5.5, iOS 15, Xcode 13 Beta 2

Part 1: WWDC 2021: AsyncSequence vs. Combine

01. Make IteratorProtocol async Using Combine

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Next episode: 02. Implement a Custom AsyncSequence

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Swift 5.5 is pretty amazing. The concurrency features are going to make life a lot easier on all of us, going forward.

// MARK: IteratorProtocol
extension EncodedModelIterator: IteratorProtocol {
  func next() -> Data? {
    <#code#>
  }
}

  }

  private var intIterator = (1...).makeIterator()
}

  func next() -> Data? {
    try? intIterator.next().map {
      try JSONEncoder().encode(<#T##value: Encodable##Encodable#>)
    }
  }

try JSONEncoder().encode(Model(int: $0))

extension EncodedModelIterator: Sequence, IteratorProtocol {

extension EncodedModelIterator: IteratorProtocol {

  }

  private let subject = PassthroughSubject<Data, Error>()
  private var intIterator = (1...).makeIterator()

  func next() -> Data? {
    do {
      guard let data = ( try intIterator.next().map {
        try JSONEncoder().encode(Model(int: $0))
      } ) else {
        return nil
      }

      return data
    } catch {
      return nil
    }
  }

      }

      subject.send(data)
      return data

    } catch {
      subject.send(completion: .failure(error))
      return nil
    }

  func resume() {
    Timer.publish(every: 2 / 3, on: .main, in: .default)
      .autoconnect()
      .sink { [unowned self] _ in _ = next() }
  }

  private var intIterator = (1...).makeIterator()
  private var cancel: (() -> Void)?
}

  func resume() {
    cancel = Timer.publish(every: 2 / 3, on: .main, in: .default)
      .autoconnect()
      .sink { [unowned self] _ in _ = next() }
      .cancel
  }

  func stop() {
    cancel?()
  }

final class EncodedModelIterator {
  var publisher: AnyPublisher<Data, Error> {
    subject.eraseToAnyPublisher()
  }

  func resume() {

struct ContentView {
  private let syncIterator = EncodedModelIterator()
}

struct ContentView {
  private let syncIterator = EncodedModelIterator()
  
  @State private var publishedModel: Model?
}

        Button {
          _ = syncIterator.next()
        } label: {

    VStack {
      IteratorView(
        title: "Combine",
        syncIterator: syncIterator,
        model: $publishedModel
      )
    }

      )
        .onReceive(
          syncIterator.publisher
            .decode(type: Model.self, decoder: JSONDecoder())
        ) {
          publishedModel = $0
        }

            .decode(type: Model.self, decoder: JSONDecoder())
            .map { $0 }
            .replaceError(with: nil)
        ) {