Swift-Closures

  https://www.weheartswift.com/closures/

• Currying  柯里化
  • e.g.1

  • //返回值爲  參數爲Int返回值爲Int的閉包
    func addTo(adder: Int) -> Int -> Int {
         return {
              num in 
              return num + adder
               }
    }
    
    let addTwo = addTo(2) 
    /* 
    addTwo = (num: Int) -> Int {
        return num + 2
    }
    */
    
    let result =addTwo(6)

     

  • e.g.2

  • //$0 閉包默認的第一個參數
    func greaterThan(comparer:Int) -> Int -> Bool {
            return {$0 > comparer}
    }
    
    let greaterThan10 = greaterThan(10)
    
    greaterThan10(12)
    greaterThan10(9)

     

  • e.g.3

  • func makeIterator(from start: Int, step: Int) -> () -> Int {
        var i = start
        return {
            let currentValue = i
            i += step
            return currentValue
        }
    }
    
    var iterator = makeIterator(from: 1, step: 1)
    
    iterator() // 1
    iterator() // 2
    iterator() // 3
    
    var anotherIterator = makeIterator(from: 1, step: 3)
    
    anotherIterator() // 1
    anotherIterator() // 4
    anotherIterator() // 7
    anotherIterator() // 10

     

• Closures in Swift (原做者的警告⚠️：When you have a new hammer everything starts to look like a nail.)
  • 　　Array: Sort, Map, Filter, Reduce
    • Sort

    • var array = [3, 4, 5]
      array.sort(by: >) 
      
      // > is defined as function
      // sort does not return a new array
      // the original array has been changed

       

    • Reduce

    • sum = array.reduce(0, {$0 + $1})
      
      // or 
      
      sum = array.reduce(0, +) // operators are methods in Swift

       

• • • Map

    • let array = [2, 3, 4]
      
      /// result is  [3, 4, 5]
      
      array.map{ $0 + 1}

       

    • Filter

    • let array = [2, 3, 4]
      let newArray = array.filter({ $0 > 3})
      //newArray = [4]