Errors when checking whether it's a $user or $node

With PHP < 5.5, this results in an error:

  //Determine if it's a user or node
  $node = isset($form_state['node']) && !empty($user = is_object($form_state['node']));
  $user = isset($form_state['user']) && is_object($form_state['user']) && !empty($form_state['user']);
 

Because empty() only supports variables. Also, $user is being set and then being reassigned on the next line.