ReflectionFunction是如何工作的？

I'm trying to use the following function to loop through loaded files and find depreciated functions.

//loads all files
include dirname(__FILE__) . '/loader.php'; 

$functions = get_defined_functions();

foreach ($functions['user'] as $func) {

    $rf = new ReflectionFunction('$func');
    var_dump($rf->isDeprecated());
}

Some functions have markup like the following, yet it's still return false. In fact every single function returns false yet there are a lot with markup stating @deprecated.

 **
 *
 * @since 0.71
 * @deprecated 1.5.1
 * @deprecated Use get_post()
 *
 * @param int $postid
 * @return array
 */

ref: http://www.php.net/manual/en/class.reflectionfunction.php