A generic singleton

Creating a singleton class is just a few lines of code, and with the difficulty of making a generic singleton i always write those lines of code.

public class Singleton
{
    private Singleton() {}
    static Singleton() {}
    private static Singleton _instance = new Singleton();
    public static Singleton Instance { get { return _instance; }}
}

The

private static Singleton _instance = new Singleton();

line removes the need for locking, as a static constructor is thread safe.

Well, it isn't really singleton - since you can't control T, there can be as many T instances as you like.

(removed thread-race; noted the double-checked usage)

I've deleted my previous answer as I hadn't noticed the code which checks for non-public constructors. 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.

I'd personally create the instance in a static constructor for simple thread safety, too.

Basically I'm not much of a fan - it's pretty easy to create singleton classes, and you shouldn't be doing it that often anyway. Singletons are a pain for testing, decoupling etc.