Question

I have a number of classes doing different things but using the same Singleton pattern from http://www.yoda.arachsys.com/csharp/singleton.html

public sealed class Singleton
{
static Singleton instance=null;
static readonly object padlock = new object();

Singleton()
{
}

public static Singleton Instance
{
    get
    {
        lock (padlock)
        {
            if (instance==null)
            {
                instance = new Singleton();
            }
            return instance;
        }
    }
}
}

Does anyone have a neat way I can reuse as much of the common Singleton code as possible between the different classes?

For example if I have SingletonJob1 and SingletonJob2 I’d like to be able to change the code in only place if I move to one of the other Singleton patterns.

Edit: Yes as people have pointed out Method 5 from http://www.yoda.arachsys.com/csharp/singleton.html is less code. I did read to the end of the page! I chose method 2 because the Singleton objects relate to hardware devices and I want only want a couple of them initialised and used in any given run of the program. Method 5 will initialise them all straight away.

Answer 1

Is there any reason you’re using that version rather than the simpler one which just initializes the instance in the declaration?

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

    // Only use this if you really need it - see the page for details
    static Singleton() {}

    private Singleton()
    {
        // I assume this logic varies
    }
}

This pattern is sufficiently short that I don’t think it’s much of a problem to include it everywhere.

I would urge you to consider whether you really need that many singletons; they’re generally not great for testability etc.

EDIT: If you really, really want laziness and you’re using .NET 4, you can get it with the 6th pattern which is on the singleton page’s new home:

public sealed class Singleton
{
    private static readonly Lazy<Singleton> lazy =
        new Lazy<Singleton>(() => new Singleton());

    public static Singleton Instance { get { return lazy.Value; } }

    private Singleton()
    {
    }
}