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  • Ch4. Filtering Operators
    Ray Wenderlich/Combine 2021. 2. 12. 01:44

    filter(_:)

    let numbers = (1...10).publisher
      
    numbers
      .filter { $0.isMultiple(of: 3) }
      .sink(receiveValue: { n in
        print("\(n) is a multiple of 3!")
      })
      .store(in: &subscriptions)
    
    3 is a multiple of 3!
    6 is a multiple of 3!
    9 is a multiple of 3!
    

     

    removeDuplicates()

    let words = "hey hey there! want to listen to mister mister ?"
    	              .components(separatedBy: " ")
                      .publisher
    
    words
      .removeDuplicates()
      .sink(receiveValue: { print($0) })
      .store(in: &subscriptions)
    hey
    there!
    want
    to
    listen
    to
    mister
    ?

     

    compactMap(_:)

    let strings = ["a", "1.24", "3", "def", "45", "0.23"].publisher
      
    strings
      .compactMap { Float($0) }
      .sink(receiveValue: {
        print($0)
      })
      .store(in: &subscriptions)
    1.24
    3.0
    45.0
    0.23
    

     

    ignoreOutput()

    let numbers = (1...10_000).publisher
      
    numbers
      .ignoreOutput()
      .sink(receiveCompletion: { print("Completed with: \($0)") },
            receiveValue: { print($0) })
      .store(in: &subscriptions)
    Completed with: finished



    Finding values

    first(where:_)

    let numbers = (1...9).publisher
      
    numbers
    	.print("numbers")
      .first(where: { $0 % 2 == 0 })
      .sink(receiveCompletion: { print("Completed with: \($0)") },
            receiveValue: { print($0) })
      .store(in: &subscriptions)
    
    numbers: receive subscription: (1...9)
    numbers: request unlimited
    numbers: receive value: (1)
    numbers: receive value: (2)
    numbers: receive cancel
    2
    Completed with: finished
    

    로그에서 볼 수 있듯이 3부터는 이벤트도 전달되지 않았다. 2를 찾고 바로 시퀀스 종료

    last(where:_)

    let numbers = (1...9).publisher
      
    numbers
      .last(where: { $0 % 2 == 0 })
      .sink(receiveCompletion: { print("Completed with: \($0)") },
            receiveValue: { print($0) })
      .store(in: &subscriptions)
    
    8
    Completed with: finished

    last(where:)은 first(where:)과 반대로 시퀀스가 종료되어야 찾고자 하는 값을 찾을 수 있다.

     

    Dropping values

    RxSwift의 Skip과 동일한 기능

    let numbers = (1...10).publisher
      
    numbers
      .dropFirst(8)
      .sink(receiveValue: { print($0) })
      .store(in: &subscriptions)
    
    9
    10
    

     

    drip(while:_)

    let numbers = (1...10).publisher
      
    numbers
      .drop(while: { $0 % 5 != 0 })
      .sink(receiveValue: { print($0) })
      .store(in: &subscriptions)
    
    5
    6
    7
    8
    9
    10

     

    drop(untilOutputFrom:_)

    et isReady = PassthroughSubject<Void, Never>()
    let taps = PassthroughSubject<Int, Never>()
      
    taps
    	.drop(untilOutputFrom: isReady)
      .sink(receiveValue: { print($0) })
      .store(in: &subscriptions)
    
    (1...5).forEach { n in
      taps.send(n)
      
      if n == 3 {
        isReady.send()
      }
    }
    4
    5

    Limiting values

    let numbers = (1...10).publisher
      
    numbers
      .prefix(2)
      .sink(receiveCompletion: { print("Completed with: \($0)") },
      		receiveValue: { print($0) })
      .store(in: &subscriptions)
    
    1
    2
    Completed with: finished
    

    prefix(while:_)

    let numbers = (1...10).publisher
      
    numbers
      .prefix(while: { $0 < 3 })
      .sink(receiveCompletion: { print("Completed with: \($0)") },
            receiveValue: { print($0) })
      .store(in: &subscriptions)
    
    1
    2
    Completed with: finished

    prefix(until:_)

    let isReady = PassthroughSubject<Void, Never>()
    let taps = PassthroughSubject<Int, Never>()
      
    taps
      .prefix(untilOutputFrom: isReady)
      .sink(receiveCompletion: { print("Completed with: \($0)") },
            receiveValue: { print($0) })
      .store(in: &subscriptions)
      
    (1...5).forEach { n in
      taps.send(n)
      
      if n == 2 {
        isReady.send()
      }
    }
    1
    2
    Completed with: finished
    

    'Ray Wenderlich > Combine' 카테고리의 다른 글

    Ch5. Combining Operators  (0) 2021.02.12
    Ch4. Filtering Operators  (0) 2021.02.12
    Ch3. Transforming Operators  (0) 2021.01.27
    Ch2. Publishers & Subscribers  (0) 2021.01.27
    Ch1. Hello, Combine!  (0) 2021.01.27

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