Swift 单例

final public class MySingle {        private static var _shared:MySingle?        public static var shared:MySingle!{        get{            if _shared == nil {                _shared = MySingle()                return _shared!            }            return _shared!        }    }        private init(){}        public func trace(str:String)->Void{        print(str)    }}MySingle.shared.trace(str: "OK")

//这是一般程序的常用写法，在swift中同样通用

第二种更简单的写法

class A{        static let shared = A()        private init() {            }}