How to turn public constructor into protected in child class?

Question

I am trying to extend the PDO class as well as turn it into a singleton. The only problem is that PDO's constructor is public, and PHP will not let me override it as a protected method. Is there any imaginative way around this? Will I be stuck with that loose end forever if I attempt this? An alternative may be not to extend PDO, but rather hold it in a static property, and do operations with it, but I wanted my class to retain all of the functionality of PDO if possible.

Answer 1

You can just wrap the PDO class in your own "Singleton Factory" object. Basically, you implement your own singleton that contains a (single) PDO instance. (Note that I don't know PHP syntax so this is Java, but you should be able to get the idea)

MySingletonFactory.getInstance().getPDO();

A more verbose explaination can be found here: http://www.wikijava.org/wiki/Singleton_Factory_patterns_example

(Again, Java ... sorry - but I believe it'll get you where you where you want to go)

Answer 2

Try this:

class MyPdoSingleton {

    protected $pdo;

    // Your own constructor called the first time if the singleton
    // instance does not exist
    protected function __construct() {
    }

    // Always returns the same instance (singleton)
    public static function getInstance() {
        static $instance;
        return (is_object($instance)) ? $instance : $instance = new self();
    }

    // Redirect any non static methods calls made to this class to the contained
    // PDO object.
    public function __call($method, $args) {
        return call_user_func_array(array($this->pdo, $method), $args);
    }

    // 5.3+
    public function __callStatic($method, $args) {
        $inst = self::getInstance();
        return call_user_func_array(array($inst, $method), $args);
    }

    // Or if you intend to have other classes inherit from this one
    /*public function __callStatic($method, $args) {
        $class = get_called_class();
        $inst = call_user_func(array($class, 'getInstance'));
        return call_user_func_array(array($inst, $method), $args);
    }*/

    public function myOtherMethod($arg) {
         // __call would not get called when requesting this method
    }
}

// Pre 5.3 use
$db = MyPdoSingleton::getInstance();
$db->myOtherMethod();

// Post 5.3 use
MyPdoSingleton::myOtherMethod();

Ops. I totally messed that up. That's what I get for answering questions first thing in a morning.