title: Printing to console from Completion Handler in Swift Playground
body: <p>I wanted to experiment with using NSURLSession to get RSS data, to see what that would look like. I wrote a chunk of code in a Playground, and when that didn't work I gutted the completion handler code and put in a print("hello, world") to verify the block was getting run.</p>
  
  <pre><code>let session = NSURLSession(configuration: NSURLSessionConfiguration.defaultSessionConfiguration())
  let task = session.dataTaskWithURL(NSURL(string:"http://apod.nasa.gov/apod.rss")!, completionHandler:
  {(data:NSData?, response:NSURLResponse?, error:NSError?) in
      print("hello, world")
  }
  )!
  task.resume()
  </code></pre>
  
  <p>In a Playground, nothing gets printed to the console. However I dropped this code into an Xcode project and it worked just fine. Why?</p>