note 72009 added to language.oop5.patterns

Thanks for the example below of an extendable Singleton. I have enhanced it a little so the derived class does not need to implement any functions. The technique to get an instance is now $x = Singleton::connect( "derived_class_name") <?php class Singleton { /* How to use: extend new class from singleton To connect: $x = Singleton::connect( "CLASSNAME" ) ; */ private static $instanceMap = array(); //protected constructor to prevent outside instantiation protected function __construct() { } //deny cloning of singleton objects public final function __clone() { trigger_error('It is impossible to clone singleton', E_USER_ERROR); } public function connect( // return a (reference to) a single instance of className $className // name of a class derived from Singleton ) { // see if class already constructed if(!isset(self::$instanceMap[$className])) { // if not then make one $object = new $className; //Make sure this object inherit from Singleton if($object instanceof Singleton) { // save in static array self::$instanceMap[$className] = $object; } else { throw SingletonException("Class '$className' do not inherit from Singleton!"); } } // return reference to single instanace of className return self::$instanceMap[$className]; } } ?> <?php class A extends Singleton { protected $rndId; protected function __construct() { $this->rndId = rand(); } public function whatAmI() { echo 'I am a ' . get_class( $this ) . ' (' . $this->rndId . ')<br />'; } } class B extends A { } $a = Singleton::connect( "A" ); $b = Singleton::connect( "B" ); $a->whatAmI();// should echo 'I am a A(some number) $b->whatAmI();// should echo 'I am a B(some number) unset( $a ) ; $c = Singleton::connect( "A" ); $d = Singleton::connect( "B" ); $c->whatAmI();// should echo 'I am a A(same number as above) $d->whatAmI();// should echo 'I am a B(same number as above) $a = new A();// this should fail $b = new B();// this should fail ?> ---- Server IP: 203.16.234.91 Probable Submitter: 211.29.230.72 ---- Manual Page -- http://www.php.net/manual/en/language.oop5.patterns.php Edit -- https://master.php.net/note/edit/72009 Del: integrated -- https://master.php.net/note/delete/72009/integrated Del: useless -- https://master.php.net/note/delete/72009/useless Del: bad code -- https://master.php.net/note/delete/72009/bad+code Del: spam -- https://master.php.net/note/delete/72009/spam Del: non-english -- https://master.php.net/note/delete/72009/non-english Del: in docs -- https://master.php.net/note/delete/72009/in+docs Del: other reasons-- https://master.php.net/note/delete/72009 Reject -- https://master.php.net/note/reject/72009 Search -- https://master.php.net/manage/user-notes.php