title: Using @available with stored properties
body: <p>I have an app that uses local notifications and supports iOS 10. I am trying to add iOS 9 support which requires me to use the old location notification API. I am trying to use <code>@available</code> and <code>#available</code> on my iOS 10 code and I can't figure out how to get my center variable to only be for devices running iOS 10.</p>
  <p>When I set my target from iOS 10  to 9 I get the error message for this variable:</p>
  <pre><code>UNUserNotificationCenter is only available on iOS 10.0 or newer.
  </code></pre>
  <p>It suggests I add <code>@available(iOS 10.0, *)</code> to my entire class which I don't want to do since there is code in this class that will be used for iOS 9. I appreciate any suggestions on how to limit my center property to just iOS 10.</p>
  <pre><code>class ViewController: UIViewController, UITextFieldDelegate {
    
    let center = UNUserNotificationCenter.current()
    ...
  }
  </code></pre>