title: Swift: Get double value from 'index' in enumeration
body: <p>In a simple Swift enumeration like this:</p>
  
  <pre><code>for (index, value) in enumerate(array) {
          let indexValue = idx as NSNumber
          let double = indexValue.doubleValue
          .... }
  </code></pre>
  
  <p>is there an easier way to convert the 'index' value to a double?</p>