title: NSOperation vs Grand Central Dispatch
body: <p>I'm learning about concurrent programming for iOS. So far I've read about <a href="http://www.cimgf.com/2008/02/16/cocoa-tutorial-nsoperation-and-nsoperationqueue/"><code>NSOperation</code>/<code>NSOperationQueue</code></a> and <a href="https://en.wikipedia.org/wiki/Grand_Central_Dispatch"><code>GCD</code></a>. <strong>What are the reasons for using <code>NSOperationQueue</code> over <code>GCD</code> and vice versa?</strong></p>
  
  <p>Sounds like both <code>GCD</code> and <code>NSOperationQueue</code> abstract away the explicit creation of <code>NSThreads</code> from the user. However the relationship between the two approaches isn't clear to me so any feedback to appreciated!</p>