infinity/registry

<?PHP
    NAMESPACE ILLI\Bug;
    INTERFACE Foo {}
    CLASS Instance IMPLEMENTS Foo
    {
        private static $instances = [];

        public static function getInstance()
        {
            $thread = get_called_class();

            if(TRUE === array_key_exists($thread, self::$instances))
                return self::$instances[$thread];       // break point

            self::$instances[$thread] = new self;
            return self::$instances[$thread];
        }

        private static $counter = 0;

        private function __construct()
        {
            static::$counter++;

            if(static::$counter < 4)
            {
                //var_dump(self::getInstance() instanceOf Foo); // trigger infinity... why?
                var_dump(self::getInstance());          // void (displays nothing)
                var_dump(self::$instances);         // void (displays nothing) when calling self::getInstance()
                return;
            }

            var_dump(self::$instances);
            var_dump(debug_backtrace(0, 4));
            die();
        }
    }