title: Who passed the arguments to the parameters of the complition handler closure?
body: <pre><code>func startUpdates(from start: Date, 
        withHandler handler: @escaping CMPedometerHandler)
  
  typealias CMPedometerHandler = (CMPedometerData?, Error?) -&gt; Void
  </code></pre>
  
  <p>The above function retrieves the pedometer data from your iOS device. When I called the function the only argument I need passed to is the parameter <code>from start</code>.</p>
  
  <p>Who actually initialized the parameter list of the completion handler closure? The <code>startUpdates</code> function I've called? </p>