title: 'NSFastEnumerator.Element' (aka 'Any') has no subscript members
body: <p>I was going through this <a href="https://www.appcoda.com/expandable-table-view/" rel="nofollow">appcoda blog</a> and came across a function where I have to get indices of visible rows. I am learning and implementing <code>Swift 3</code> / <code>Xcode 8</code>. I get <code>No subscript members</code> error for the following function.</p>
  
  <pre><code>func getIndicesOfVisibleRows() {
      visibleRowsPerSection.removeAll()
  
      for currentSectionCells in cellDescriptors {
          var visibleRows = [Int]()
  
          for row in 0...((currentSectionCells as! [[String: AnyObject]]).count - 1) {
              if currentSectionCells[row]["isVisible"] as! Bool == true { //Get compile time error here
                  visibleRows.append(row)
              }
          }
  
          visibleRowsPerSection.append(visibleRows)
      }
  }
  </code></pre>
  
  <p>How do I get object of <code>currentSectionCells</code> array whose object for key is "<code>isVisible</code>" here?</p>