void Main(){    object.ReferenceEquals(Singleton.GetInstance(),Singleton.GetInstance()).Dump();    object.ReferenceEquals(NSingleton.Instance,NSingleton.Instance).Dump();}class Singleton{    private Singleton(){}    private static Singleton instance;    private static object obj = new object();    public static Singleton GetInstance(){        if (instance==null)        {            lock (obj)            {                if (instance==null)                {                    instance=new Singleton();                }            }        }        return instance;    }}class NSingleton{    public static readonly NSingleton Instance = new NSingleton();}