Reactive Programming in iOS with Combine

Feb 4 2021 · Swift 5.3, macOS 11.0, Xcode 12.2

Part 4: Timing, Scheduling and Sequencing Operators

28. Sequencing Operators

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Previous episode: 27. Scheduling Operators Next episode: 29. Challenge: Sequence Operators

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On their surface, Publishers are really just sequences, and set of sequence operators in Combine let you work with the sequence as a whole instead of individual values. As we go through these operators, you’ll notice that many have the same names as functions from the Swift Standard Library - but be sure to note any differences between those functions and the operators in Combine when you use them in your code.

example(of: "min") {
  // 1
  let publisher = [1, -50, 246, 0].publisher

  // 2
  publisher
    .print("publisher")
    .min()
    .sink(receiveValue: { print("Lowest value is \($0)") })
    .store(in: &subscriptions)
}

example(of: "max") {
  // 1
  let publisher = ["A", "F", "Z", "E"].publisher

  // 2
  publisher
    .print("publisher")
    .max()
    .sink(receiveValue: { print("Highest value is \($0)") })
    .store(in: &subscriptions)
}

example(of: "count") {
  let publisher = ["A", "B", "C"].publisher

  publisher
    .print("publisher")
    .count()
    .sink(receiveValue: { print("I have \($0) items") })
    .store(in: &subscriptions)
}


example(of: "output(at:)") {

  let publisher = ["A", "B", "C"].publisher

  publisher
    .print("publisher")
    .output(at: 1)
    .sink(receiveValue: { print("Value at index 1 is \($0)") })
    .store(in: &subscriptions)
}

example(of: "output(in:)") {
  let publisher = ["A", "B", "C", "D", "E"].publisher

  publisher
    .output(in: 1...3)
    .sink(receiveCompletion: { print($0) },
          receiveValue: { print("Value in range: \($0)") })
    .store(in: &subscriptions)
}