Question

I have this code running on PHP 5.2.6

class Singleton {
    static private $instance = false;
    private $id = false;
    protected function __construct() {
        $this->id = uniqid();
    }

    static public function instance() {
        if (!self :: $instance) {
            self :: $instance = new self();
        }
        return self :: $instance;
    }
    public function get_id() {
        return $this->id;
    }
}

class Chucknorris extends Singleton {

}

echo "php version = ".phpversion()."<br>";

$singleton = Singleton::instance();
echo get_class($singleton)."<br>";
echo "singleton id = ".$singleton->get_id()."<br>";

$chucknorris = Chucknorris::instance();
echo get_class($chucknorris)."<br>";
echo "chucknorris id = ".$chucknorris->get_id()."<br>";

Here’s the output

php version = 5.2.6
Singleton
singleton id = 4ea7dca7d8f23
Singleton
chucknorris id = 4ea7dca7d8f23

When I ask for an instance of Chucknorris, I always get the Singleton one. I’d like to find out a way to extend the Singleton.

I know we can use get_called_class method to do it but it comes only with PHP 5.3. Is there anyway I can extend a Singleton without redefining the design pattern in the extended classes ?

Answer 1

Why don’t you simulate the get_class_function if it doesn’t exist with 5.3 PHP version ?
This code may answer your question.

if (!function_exists('get_called_class')) {
    function get_called_class() {
        $bt = debug_backtrace();
        $lines = file($bt[1]['file']);
        preg_match(
            '/([a-zA-Z0-9\_]+)::'.$bt[1]['function'].'/',
            $lines[$bt[1]['line']-1],
            $matches
        );
        return $matches[1];
    }
}

abstract class Singleton {
    private $id = false;

    protected function __construct() {
        $this->id = uniqid();
    }

    static public function instance() {
        static $instances = array();
        $called_class_name = get_called_class();
        if (!isset($instances[$called_class_name])) {
            $instances[$called_class_name] = new $called_class_name();
        }
        return $instances[$called_class_name];
    }

    public function get_id() {
        return $this->id;
    }
}

class Chucknorris extends Singleton {}
class Brucelee extends Singleton {}

echo "php version = ".phpversion()."<br>";

$chucknorris = Chucknorris::instance();
echo get_class($chucknorris)."<br>";
echo "chucknorris id = ".$chucknorris->get_id()."<br>";

$brucelee = Brucelee::instance();
echo get_class($brucelee)."<br>";
echo "brucelee id = ".$brucelee->get_id()."<br>";