PHP function in XML?

dom-processing-instructions.php

<?php
/**
 * PHP function in XML?
 * @link http://stackoverflow.com/q/14888921/367456
 * @link https://gist.github.com/hakre/4959346
 * @link http://eval.in/9908
 * @author hakre <hakre.wordpress.com>
 */

$xml = <<<BUFFER
<doThis><?php
    function doThis()
    {
        return 'bang bang bang!';
    }
?></doThis>
BUFFER;

/**
 * XML PHP Processing Instruction Parser
 *
 * Generate Object based on PHP processing instructions.
 */
class PiDOMDocument extends DOMDocument
{
    public function getObject($class = null)
    {
        $class || $class = uniqid(__CLASS__);

        $xp     = new DOMXPath($this);
        $buffer = '';

        foreach ($xp->query('processing-instruction("php")') as $pi) {
            $buffer .= "\n" . $pi->data;
        }

        eval(sprintf("class %s {\n%s\n}", $class, $buffer));

        return new $class;
    }
}


echo "PiDOMDocument:\n==============\n";

$doc = new PiDOMDocument();
$doc->loadXML($xml);
$obj = $doc->getObject();
echo $obj->doThis();

echo "\n\nPiSimpleXMLElement:\n===================\n";

/**
 * SimpleXMLElement integration of PiDOMDocument
 */
class PiSimpleXMLElement extends SimpleXMLElement
{
    public function __call($name, $args) {
        $doc = new PiDOMDocument();
        $doc->loadXML($this->asXML());
        $callback = array($doc->getObject(), $name);
        return call_user_func_array($callback, $args);
    }
}

$foo = simplexml_load_string($xml, 'PiSimpleXMLElement');
echo $foo->doThis();   //bang bang bang!