Vererbung Singleton; Gewährleistung, dass Kind-Klassen Singletons sind, spätere Kind-Klassen aber nicht irgendetwas anderes werden können

instance-kein_kind.php

abstract class aloneSingleton {

    private static $_instance;
    
    final public static function getInstance() {

        if ( ! is_null( self::$_instance ) ) {
            if ( get_class(self::$_instance) !== get_called_class() )
                throw new LogicException(get_called_class() . ' is an subclass of ' . __CLASS__
                    . ', instances are restricted to one instance overall, '
                    . 'you tried to access the wrong stage of inheritance, use '
                    . get_class(self::$_instance) . ' instead.');
            else return self::$_instance;
        } else {
            self::$_instance = new static;
        }
        
        return self::$_instance;
    }

    abstract protected function __construct();

}

class A extends aloneSingleton {
    
    protected function __construct() { echo __CLASS__.' created.'; }
    
}

class B extends aloneSingleton {

    protected function __construct() { echo __CLASS__ . ' created.'; }

}

class C extends A {

    protected function __construct() { echo __CLASS__ . ' created.'; }

}

class D extends B {

    protected function __construct() { echo __CLASS__ . ' created.'; }

} 

Singleton.php

class Singleton {

    private static $_instances = array();

    final public static function getInstance() {
        return ! isset( self::$_instances[ get_called_class() ] )
                ? self::$_instances[ get_called_class() ] = new static
                : self::$_instances[ get_called_class() ];
    }
    
    final protected function __clone() {
    }
    
    protected function __construct () {
        
        echo __CLASS__ . '-Class representation of construct.' . "\n";
    }

}

class superSingleton extends Singleton {
    
    protected function __construct () {
        
        echo __CLASS__ . '-Class representation of construct.' . "\n";
    }
    
}