Creating the Singleton design pattern in PHP5

Question

How would one create a Singleton class using PHP5 classes?

Answer 1

PHP 5.3 allows the creation of an inheritable Singleton class via late static binding:

class Singleton
{
    protected static $instance = null;

    protected function __construct()
    {
        //Thou shalt not construct that which is unconstructable!
    }

    protected function __clone()
    {
        //Me not like clones! Me smash clones!
    }

    public static function getInstance()
    {
        if (!isset(static::$instance)) {
            static::$instance = new static;
        }
        return static::$instance;
    }
}

This solves the problem, that prior to PHP 5.3 any class that extended a Singleton would produce an instance of its parent class instead of its own.

Now you can do:

class Foobar extends Singleton {};
$foo = Foobar::getInstance();

And $foo will be an instance of Foobar instead of an instance of Singleton.