1. 排序函數(shù)

func sorted(by areInIncreasingOrder: (Element, Element) throws -> Bool) rethrows -> [Element]

        var names: [String] = ["61","95","8","248","42"]
        //一個包含字符串的數(shù)組
        names = names.sorted(by: { (s1, s2) -> Bool in
            return s1 < s2
        })
        print(names) //輸出結(jié)果

該高階函數(shù)內(nèi)部大概實(shí)現(xiàn):

extension Array {
    
    typealias  IncreasingOrder = (String,String) -> Bool
    
    mutating func mySorted(_ increasingOrder:IncreasingOrder) -> [String] {
        var newString:[String] = [String]()

        // 假設(shè)這里采用簡單選擇排序
        for n in 0..<self.count{
            var tamper:String = self[n] as! String
            for i in n+1..<self.count {  //
                var next:String = self[i] as! String
                guard !increasingOrder(tamper,next) else {
                    continue
                }
                swap(&tamper, &next)
                swap(&self[n], &self[i])
            }
            newString.append(tamper)
        }
        return newString
    }
}

2. First函數(shù)

func first(where predicate: (Element) throws -> Bool) rethrows -> Element?

        let names:[String] = ["61","95","8","248","42"]
        //第一個滿足條件的值
        let name = names.first { (first) -> Bool in
            return first == "8"
            }!
        print(name) // 輸出: 8

3. Map函數(shù)

func map<T>(_ transform: (Element) throws -> T) rethrows -> [T]

        var names:[String] = ["61","95","8","248","42"]
        // 在每個字符前加上$
        names = names.map { (str) -> String in
            "$" + str
        }
        print(names) // ["$61", "$95", "$8", "$248", "$42"]

4. compactMap函數(shù)

flatMap 方法同 map 方法比較類似网持，只不過它返回后的數(shù)組中不存在 nil（自動把 nil 給剔除掉），同時它會把 Optional 解包

        let array = ["Apple", "Orange", "Grape", ""]
        
        let arr1 = array.map { a -> Int? in
            let length = a.count
            guard length > 0 else { return nil }
            return length
        }
        print("arr1:\(arr1)") // [Optional(5), Optional(6), Optional(5), nil]
        
        let arr2 = array.compactMap { a-> Int? in
            let length = a.count
            guard length > 0 else { return nil }
            return length
        }
        print("arr2:\(arr2)")// [5, 6, 5]

5. filter函數(shù)

篩選滿足條件的數(shù)據(jù)

        var names:[String] = ["61","95","8","248","42"]
        
        names = names.filter({ (str) -> Bool in
           return str.count > 1
        })
        print(names) // ["61", "95", "248", "42"]

6. reduce函數(shù)

計算, 可以對數(shù)組中的元素進(jìn)行計算

let array = [1, 2, 3, 4]
        //計算數(shù)組array元素的和
        //在這里$0和$1的意義不同姚淆，$0代表元素計算后的結(jié)果促绵，$1代表元素
        //0代表初始化值踱侣，在這里可以理解為 $0初始值 = 0
        let result = array.reduce(0){
            $0 + $1
        }
        print(result) // 10