static public function count($countable, $count, $message = null, $propertyPath = null)
        {
            if ($count !== count($countable)) {
                $message = $message ?: sprintf(
                    'List does not contain exactly "%d" elements.',
                    static::stringify($countable),
                    static::stringify($count)
                );

                throw static::createException($countable, $message, static::INVALID_COUNT, $propertyPath, array('count' => $count));
            }
        }