gistfile1.aw

<?

class A {

    static $instance = null;

    public static function getInstance(){
        if(is_null(self::$instance)){
            self::newInstance();
        }   

        return self::$instance;
    }   

    public static function newInstance(){
       self::$instance = static::createInstance(); 
    }   

    public static function createInstance(){
        return "from A";
    }   
}

class B extends A { 

    public static function createInstance(){
        return "from B";
    }   
}

class C extends A { 

    public static function createInstance(){
        return "from C";
    }   
}

print B::getInstance() . "\n";
print C::getInstance() . "\n";


//prints 
//from B
//from B