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

If your class is not meant to define some super-type, it should not be declared as abstract, I'd say.

In your case, I would rather go with a class :

• That defines __construct and __clone as private methods
  • so the class cannot be instanciated from outside
• And, this way, your class could create an instance of itself
  • See the Singleton design pattern, about that, btw

Now, why use a Singleton, and not only static methods ? I suppose that, at least a couple of reasons can be valid :

• Using a singleton means using an instance of the class ; makes it easier to transform a non-singleton class to a singleton one : only have to make __construct and __clone private, and add some getInstance method.
• Using a singleton also means you have access to everything you can use with a normal instance : $this, properties, ...
• Oh, a third one (not sure about that, but might have its importance) : with PHP < 5.3, you have less possibilities with static methods/data :
  • __callStatic has only been introduced in PHP 5.3
  • There is no __getStatic, __setStatic, ...
  • Same for a couple of other Magic methods !
• Late Static Binding has only been added with PHP 5.3 ; and not having it often makes it harder, when working with static methods/classes ; especially when using inheritance.

This being said, yes, some code like this :

abstract class MyClass {
    protected static $data;
    public static function setA($a) {
        self::$data['a'] = $a;
    }
    public static function getA() {
        return self::$data['a'];
    }
}

MyClass::setA(20);
var_dump(MyClass::getA());

Will work... But it doesn't feel quite natural... and this is a very simple example (see what I said earlier with Late Static Binding, and magic methods).