title: How to iterate over Stripe subscription collection
body: <p>I'm currently integrating with Stripe and before I update an existing the Subscription I need to retrieve all existing subscriptions to find the correct Subscription Id.</p>
  
  <p>However, when I use the Stripe PHP library I seem to be unable to iterate over the actual subscription collection.</p>
  
  <p>This is how I retrieve the subscription collection:</p>
  
  <pre><code>$subscriptions = $customer-&gt;subscriptions-&gt;all();
  </code></pre>
  
  <p>I have also tried this, which should be the same and doesn't seem to make difference in the end result:</p>
  
  <pre><code>$subscriptions = \Stripe\Customer::retrieve( $customer-&gt;id )-&gt;subscriptions-&gt;all();
  </code></pre>
  
  <p>For sanity sake, after obtaining the subscription collection I <code>echo</code> a <code>count()</code> on it to see how many elements it contains:</p>
  
  <pre><code>echo count( $subscriptions );  // echos '1' which is what I expect.
  </code></pre>
  
  <p>When I <code>print_r()</code> the entire <code>$subscriptions</code> object I do indeed see the one existing subscription, so I have verified that it has been retrieved.</p>
  
  <p>I then want to simply iterate over the collection with a <code>foreach</code>. This should be possible because the <code>StripeObject</code> (a base class for the returned collection) implements <code>ArrayAccess</code>:</p>
  
  <pre><code>foreach( $subscriptions as $subscription )
  {
     print_r( $subscription );
  }
  </code></pre>
  
  <p>However, this doesn't result in anything.</p>
  
  <p>How do I correctly iterate over a Stripe subscription collection?</p>