Make \Stripe\Collection implement \Countable

lib/Collection.php

@@ -10,7 +10,7 @@
  * @property bool $has_more
  * @property \Stripe\StripeObject[] $data
  */
-class Collection extends StripeObject implements \IteratorAggregate
+class Collection extends StripeObject implements \Countable, \IteratorAggregate
 {
     const OBJECT_NAME = 'list';
 
@@ -104,6 +104,14 @@ public function retrieve($id, $params = null, $opts = null)
         return Util\Util::convertToStripeObject($response, $opts);
     }
 
+    /**
+     * @return int the number of objects in the current page
+     */
+    public function count()
+    {
+        return \count($this->data);
+    }
+
     /**
      * @return \ArrayIterator an iterator that can be used to iterate
      *    across objects in the current page

tests/Stripe/CollectionTest.php

@@ -88,6 +88,19 @@ public function testCanCreate()
         ]);
     }
 
+    public function testCanCount()
+    {
+        $collection = Collection::constructFrom([
+            'data' => [['id' => 1]],
+        ]);
+        static::assertCount(1, $collection);
+
+        $collection = Collection::constructFrom([
+            'data' => [['id' => 1], ['id' => 2], ['id' => 3]],
+        ]);
+        static::assertCount(3, $collection);
+    }
+
     public function testCanIterate()
     {
         $collection = Collection::constructFrom([