class ElementCollection

abstract class ElementCollection implements Iterator {
    
    /** @var DOMElement[] */
    private $nodes = [];
    
    /** @var int */
    private $position;
    public function __construct(DOMNodeList $nodeList) {
        $this->position = 0;
        $this->importNodes($nodeList);
    }
    public abstract function current();
    public function next() : void {
        $this->position++;
    }
    public function key() : int {
        return $this->position;
    }
    public function valid() : bool {
        return $this->position < count($this->nodes);
    }
    public function rewind() : void {
        $this->position = 0;
    }
    protected function getCurrentElement() : DOMElement {
        return $this->nodes[$this->position];
    }
    private function importNodes(DOMNodeList $nodeList) : void {
        foreach ($nodeList as $node) {
            if (!$node instanceof DOMElement) {
                throw new ElementCollectionException(sprintf('\\DOMElement expected, got \\%s', get_class($node)));
            }
            $this->nodes[] = $node;
        }
    }

}