title: Get interval from DatePeriod variable
body: <p>As I understood from PHP manual page for <a href="http://php.net/manual/en/class.dateperiod.php" rel="nofollow">DatePeriod</a> class that it is purposed to store periods of time. I.e. interval with some point at time meaning start of the interval + optional recurrences.</p>
  
  <p>With the following code I create $dp variable starting today with length of one month</p>
  
  <pre><code>$start = new DateTime();
  $interval = new DateInterval('P1M');
  $end = clone $start;
  $end-&gt;add($interval);    
  $dp = new DatePeriod($start, $interval, $end);
  </code></pre>
  
  <p>With following code I am printing all (at my example only one cause there are no recurrences) start dates of the period:</p>
  
  <pre><code>foreach ($dp as $d)
      var_dump($d-&gt;d);
  </code></pre>
  
  <p>My question is how can I get interval from $dp variable?</p>