Reactive Programming in iOS with Combine

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

Part 2: Transforming & Filtering Operators

11. More Filtering Operators

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Previous episode: 10. Filtering Operators Next episode: 12. Challenge: Filter All the Things

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Now with the basics of filtering out of the way, let’s focus in on some operators that will help you refine the values you’ll send downstream to consumers.

example(of: "first(where:)") {
  // 1
  let numbers = (1...9).publisher

  // 2
  numbers
    .first(where: { $0 % 2 == 0 })
    .sink(receiveCompletion: { print("Completed with: \($0)") },
          receiveValue: { print($0) })
    .store(in: &subscriptions)
}

numbers
  .print("numbers")

example(of: "last(where:)") {
  // 1
  let numbers = (1...9).publisher

  // 2
  numbers
    .last(where: { $0 % 2 == 0 })
    .sink(receiveCompletion: { print("Completed with: \($0)") },
          receiveValue: { print($0) })
    .store(in: &subscriptions)
}

example(of: "last(where:)") {
  let numbers = PassthroughSubject<Int, Never>()

  numbers
    .last(where: { $0 % 2 == 0 })
    .sink(receiveCompletion: { print("Completed with: \($0)") },
          receiveValue: { print($0) })
    .store(in: &subscriptions)

  numbers.send(1)
  numbers.send(2)
  numbers.send(3)
  numbers.send(4)
  numbers.send(5)
  numbers.send(completion: .finished)
}

example(of: "prefix") {
  // 1
  let numbers = (1...10).publisher

  // 2
  numbers
    .prefix(2)
    .sink(receiveCompletion: { print("Completed with: \($0)") },
          receiveValue: { print($0) })
    .store(in: &subscriptions)
}

example(of: "drop(while:)") {
  // 1
  let numbers = (1...10).publisher

  // 2
  numbers
    .drop(while: { $0 % 5 != 0 })
    .sink(receiveValue: { print($0) })
    .store(in: &subscriptions)
}