如何使用 SimpleXML 在 PHP 中高效率解析 RSS/Atom 提要？

class BlogPost {
    public $date;
    public $ts;
    public $link;
    public $title;
    public $text;
}

class BlogFeed {
    public $posts = [];

    public function __construct($file_or_url) {
        $file_or_url = $this->resolveFile($file_or_url);
        if (!$x = simplexml_load_file($file_or_url)) return;

        foreach ($x->channel->item as $item) {
            $post = new BlogPost();
            $post->date = (string)$item->pubDate;
            $post->ts = strtotime($item->pubDate);
            $post->link = (string)$item->link;
            $post->title = (string)$item->title;
            $post->text = (string)$item->description;
            $post->summary = $this->summarizeText($post->text);

            $this->posts[] = $post;
        }
    }

    private function resolveFile($file_or_url) {
        if (!preg_match('|^https?:|', $file_or_url))
            $feed_uri = $_SERVER['DOCUMENT_ROOT'] .'/shared/xml/'. $file_or_url;
        else
            $feed_uri = $file_or_url;

        return $feed_uri;
    }

    private function summarizeText($summary) {
        $summary = strip_tags($summary);
        $max_len = 100;
        if (strlen($summary) > $max_len)
            $summary = substr($summary, 0, $max_len) . '...';

        return $summary;
    }
}