note 57666 deleted from language.oop by danbrown

Note Submitter: Felix M dot Palmen <fmp at palmen dot homeip dot net> ---- My way to implement a singleton in PHP4. I think it's the most convenient one since it works transparently using the constructor. Thanks to S.Radovanovic for his idea with referencing the class' variables, posted on http://www.php.net/manual/en/language.variables.scope.php <?php /* Singleton. Every instatiation returns the "same" object. * * for this to work, ALWAYS create objects with $object =& new class(). * The reference operator doesn't do any harm in general and is * necessary for singletons. * * You also need to declare all the class' variables with "var" for * a singleton subclass. But that should always be a rule of good * design :) * * call parent::singleton() first in your subclass constructor. * * Of course, the subclass constructor should check if the object is already * initialized before doing any initialization. */ class singleton { function singleton() { // static associative array containing the real objects, key is classname static $instances=array(); // get classname $class = get_class($this); if (!array_key_exists($class, $instances)) { // does not yet exist, save in array $instances[$class] = $this; } // PHP doesn't allow us to assign a reference to $this, so we do this // little trick and fill our new object with references to the original // class' variables: foreach (get_class_vars($class) as $var => $value) { $this->$var =& $instances[$class]->$var; } } } ?>