Well, it isn't really singleton - since you can't control
T, there can be as many T instances as you like.The code does check for non-public constructors, which is good. However, this is a check which is only performed at execution time - there's no compile-time check, which is a strike against it. It also relies on having enough access to call the non-public constructor, which adds some limitations.
In addition, it doesn't prohibit internal constructors - so you can end up with non-singletons.
There is an excellent article on singletons at http://www.yoda.arachsys.com/csharp/singleton.html
Here are two proper implementations:
public sealed class Singleton
{ static readonly Singleton instance = new Singleton();
// Explicit static constructor to tell C# compiler // not to mark type as beforefieldinit static Singleton() { }
Singleton()
{ }
public static Singleton Instance
{ get { return instance; }
}
}
Or simply:
public class Singleton
{ private static Singleton _instance = new Singleton();
private Singleton() {} public static Singleton Instance { get { return _instance; }}
}
Both of these classes removes the need for locking, as a static constructor is thread safe.
