I have always used a Singleton class for a registry object in PHP. As all Singleton classes I think the main method looks like this:

class registry
{
    public static function singleton()
    {
        if( !isset( self::$instance ) )
        {
            self::$instance = new registry();
        }
        return self::$instance;
    }

    public function doSomething()
    {
        echo 'something';
    }
}

So whenever I need something of the registry class I use a function like this:

registry::singleton()->doSomethine();

Now I do not understand what the difference is between creating just a normal static function. Will it create a new object if I just use a normal static class.

class registry
{
    public static function doSomething()
    {
        echo 'something';
    }
}

Now I can just use:

registry::doSomethine();

Can someone explain to me what the function is of the singleton class. I really do not understand this.