Static classes in PHP via abstract keyword?

Question

According to the PHP manual, a class like this:

abstract class Example {}

cannot be instantiated. If I need a class without instance, e.g. for

Answer 1

I wouldnt use an abstract class. Id use something more akin to a singleton with a protected/private constructor as you suggest. There should be very few static properties other than $instance which is the actual registry instance. Recently ive become a fan of Zend Frameworks typical pattern which is something like this:

class MyRegistry {

  protected static $instance = null;

  public function __construct($options = null)
  {
  }

  public static function setInstance(MyRegistry $instance)
  {
    self::$instance = $instance;
  }

  public static function getInstance()
  {
     if(null === self::$instance) {
        self::$instance = new self;
     }

     return self::$instance;
  }
}

This way you get a singleton essentially but you can inject a configured instance to use. This is handy for testing purposes and inheritance.