note 82985 added to language.oop5.patterns

If you want a singleton and you don't mind on throwing a stop error/exception when a 2nd instace is created instead of returning the already created object, then this code works with subclassing and without getInstace alike functions (just with __construct) <?php class SINGLETON { // the array for checking the created instances protected static $singletons = array (); // make it final so extended classes cannot override it final public function __construct () { $classname = get_class ( $this ); if ( ! isset ( self::$singletons[$classname] ) ) // instead of $this it could be any value since we are checking for isset, but a reference to the object may be useful in a possible improvement, somewhat self::$singletons[$classname] = $this; else // your favorite stop error here trow new Exception (); } // final as well, no overriding, plus protected so it cannot be called final protected function __clone () {} } class X extends SINGLETON { //... } class Y extends X { //... } $x = new X (); $y = new Y (); $a = new X (); // execution stops, as an instance of X is created already $b = new Y (); // execution stops, as an instance of Y is created already, it DOES NOT give problems with X, despite extending X ?> so, if it is ok to stops the execution, this method is way simpler it must stops the execution because no matter what, __construct will return a reference to the new object, always, so if the script goes on further you will have effectively 2 instances (as a matter of fact, the code above only checks the existence of another object from the same class, it does not prohibit the creation of a new one) hth ---- Server IP: 209.41.74.194 Probable Submitter: 213.60.58.100 ---- Manual Page -- http://www.php.net/manual/en/language.oop5.patterns.php Edit -- https://master.php.net/note/edit/82985 Del: integrated -- https://master.php.net/note/delete/82985/integrated Del: useless -- https://master.php.net/note/delete/82985/useless Del: bad code -- https://master.php.net/note/delete/82985/bad+code Del: spam -- https://master.php.net/note/delete/82985/spam Del: non-english -- https://master.php.net/note/delete/82985/non-english Del: in docs -- https://master.php.net/note/delete/82985/in+docs Del: other reasons-- https://master.php.net/note/delete/82985 Reject -- https://master.php.net/note/reject/82985 Search -- https://master.php.net/manage/user-notes.php