배열을 XML로 변환하는 PHP 메소드

<?php
class A2Xml {
  private $version  = &#39;1.0&#39;;
  private $encoding  = &#39;UTF-8&#39;;
  private $root    = &#39;root&#39;;
  private $xml    = null;
  function __construct() {
    $this->xml = new XmlWriter();
  }
  function toXml($data, $eIsArray=FALSE) {
    if(!$eIsArray) {
      $this->xml->openMemory();
      $this->xml->startDocument($this->version, $this->encoding);
      $this->xml->startElement($this->root);
    }
    foreach($data as $key => $value){
  
      if(is_array($value)){
        $this->xml->startElement($key);
        $this->toXml($value, TRUE);
        $this->xml->endElement();
        continue;
      }
      $this->xml->writeElement($key, $value);
    }
    if(!$eIsArray) {
      $this->xml->endElement();
      return $this->xml->outputMemory(true);
    }
  }
}
$res = array(
  &#39;hello&#39; => &#39;11212&#39;,
  &#39;world&#39; => &#39;232323&#39;,
  &#39;array&#39; => array(
    &#39;test&#39; => &#39;test&#39;,
    &#39;b&#39;  => array(&#39;c&#39;=>&#39;c&#39;, &#39;d&#39;=>&#39;d&#39;)
  ),
  &#39;a&#39; => &#39;haha&#39;
);
$xml = new A2Xml();
echo $xml->toXml($res);