Swift4.0 sorted(by:)函数理解（闭包$理解）

    override func viewDidLoad() {
        super.viewDidLoad()
        let names = ["AT", "AE", "D", "S", "BE"]
        let result1 = names.sorted(by:backwords)
        let result = names.sorted(by: {(a:String,b:String)->Bool in return a>b})
        let result2 = names.sorted(by: {$0 > $1})
        print(result)
        print(result1)
        print(result2)
    }

    func backwords(s1:String,s2:String) -> Bool {
        return s1>s2
    }