         allItemAttributes.removeAll(keepCapacity: false)
         sectionItemAttributes.removeAll(keepCapacity: false)
         
-        for  idx in 0..<columnCount {
+        for _ in 0..<columnCount {
             self.columnHeights.append(0)
         }
         

        return sectionItemAttributes[indexPath.section][indexPath.item]
    }
    
    override public func layoutAttributesForSupplementaryViewOfKind(elementKind: String, atIndexPath indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes! {
        var attribute: UICollectionViewLayoutAttributes?
        
        if elementKind == CollectionViewWaterfallElementKindSectionHeader {

            * 4. Section footer
            */
            var footerHeight: Float
            let columnIndex = longestColumnIndex()
            top = columnHeights[columnIndex] - minimumInteritemSpacing + Float(sectionInset.bottom)
            
            if let height = delegate?.collectionView?(collectionView!, layout: self, heightForFooterInSection: section) {
