title: Swift error while operations with NSNumbers
body: <p>I'm using this code in a Swift project</p>
  
  <pre><code>        var coreDataArray:NSArray = fetchFromCoreData() // Return an array of record
          var mediumValue:NSNumber
          var tmp:NSNumber
  
          for(var i = 0; i &lt; coreDataArray.count; ++i)
          {
              tmp = coreDataArray[i].score // The .score value is set as Float in .xcdatamodel
              mediumValue = mediumValue + tmp
          }
  </code></pre>
  
  <p>i get this error on the line <code>mediumValue = mediumValue + tmp</code></p>
  
  <pre><code>Could not find an overload for '+' that accepts the supplied arguments
  </code></pre>
  
  <p>Any advice??</p>