• Currying  柯里化
  • e.g.1
  • //返回值为  参数为Int返回值为Int的闭包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 闭包默认的第一个参数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() // 1iterator() // 2iterator() // 3var anotherIterator = makeIterator(from: 1, step: 3)anotherIterator() // 1anotherIterator() // 4anotherIterator() // 7anotherIterator() // 10

     
• Closures in Swift (原作者的警告⚠️：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]