Check arrays for recursion

Question

What is the best way to check if an array is recursive in PHP ?

Given the following code:

Answer 1

The following function is simpler[opinion] than the code in the accepted answer, and seems to work for any use case that I have been able to contrive. It also seems to be surprisingly fast, typically taking microseconds, though I have not done extensive benchmarking. If there is a problem with it, I would be grateful if somebody could point it out?

// returns TRUE iff the passed object or array contains
// a self-referencing object or array
function is_r($obj, &$visited=array())
  {
  $visited[] = $obj;
  foreach ($obj as $el)
    {
    if (is_object($el) || is_array($el))
      {
      if (in_array($el, $visited, TRUE))
        return TRUE;
      if (is_r($el, $visited))
        return TRUE;
      }
    }
  return FALSE;
  }