         if var firstCell = visibleCell.first {
             var leftEdge = firstCell.frame.minX
             while leftEdge > minX {
-                leftEdge = placeNewCellOnLeft(with: leftEdge, index: firstCell.index!, dataSource: dataSource)
+                leftEdge = placeNewCellOnLeft(with: leftEdge, index: firstCell.index, dataSource: dataSource)
                 firstCell = visibleCell.first!
             }
         }

        if var lastCell = visibleCell.last {
            var rightEdge = lastCell.frame.maxX
            while rightEdge < maxX {
                rightEdge = placeNewCellOnRight(with: rightEdge, index: lastCell.index!, dataSource: dataSource)
                lastCell = visibleCell.last!
            }
        }


open class PagingMenuCell: UIView {
    var identifier: String!
    var index: Int!
    var isSelected: Bool = false
}

public protocol PagingMenuViewDataSource: class {
