swift4.0 创建随机字符串

修改自https://www.jianshu.com/p/1ec6ba8a0da3

extension String{
    static let random_str_characters = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
    static func randomStr(len : Int) -> String{
        var ranStr = ""
        for _ in 0..<len {
            let index = Int(arc4random_uniform(UInt32(random_str_characters.count)))
            ranStr.append(random_str_characters[random_str_characters.index(random_str_characters.startIndex, offsetBy: index)])
        }
        return ranStr
    }
}

用法

String.randomStr(len: 30)