public function abbr($string, $delimiter = '', $option = PINYIN_DEFAULT)
    {
        if (\is_int($delimiter)) {
            list($option, $delimiter) = array($delimiter, '');
        }

        return implode($delimiter, array_map(function ($pinyin) {
            return \is_numeric($pinyin) ? $pinyin : mb_substr($pinyin, 0, 1);
        }, $this->convert($string, $option)));
    }