Ambiguous use of 'subscript' - ios 9 Swift 2.0

Question

I was writing ios app using Swift 2.0 on xcode 7.0. Before updating to the last version of xCode 7.1 the same exact code was working perfectly

After the update i got this error:

Ambiguous use of 'subscript'

in those lines:

  override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> (UICollectionViewLayoutAttributes!) {
    return self.itemAttributes[indexPath.section][indexPath.row] as! UICollectionViewLayoutAttributes
  }

this is the full class:

class CustomCollectionViewLayout: UICollectionViewLayout {

  var numberOfColumns = 7 // the number of columns
  var itemAttributes : NSMutableArray!
  var itemsSize : NSMutableArray!
  var contentSize : CGSize!

  func setColumnNumber(columnNum: Int) {
    numberOfColumns = columnNum
  }

  override func prepareLayout() {
    if self.collectionView?.numberOfSections() == 0 {
      return
    }

    if (self.itemAttributes != nil && self.itemAttributes.count > 0) {
      for section in 0..<self.collectionView!.numberOfSections() {
        let numberOfItems : Int = self.collectionView!.numberOfItemsInSection(section)
        for index in 0..<numberOfItems {
          if section != 0 && index != 0 {
            continue
          }

          let attributes : UICollectionViewLayoutAttributes = self.layoutAttributesForItemAtIndexPath(NSIndexPath(forItem: index, inSection: section))
          if section == 0 {
            var frame = attributes.frame
            frame.origin.y = self.collectionView!.contentOffset.y
            attributes.frame = frame
          }

          if index == 0 {
            var frame = attributes.frame
            frame.origin.x = self.collectionView!.contentOffset.x
            attributes.frame = frame
          }
        }
      }
      return
    }

    if (self.itemsSize == nil || self.itemsSize.count != numberOfColumns) {
      self.calculateItemsSize()
    }

    var column = 0
    var xOffset : CGFloat = 0
    var yOffset : CGFloat = 0
    var contentWidth : CGFloat = 0
    var contentHeight : CGFloat = 0

    for section in 0..<self.collectionView!.numberOfSections() {
      let sectionAttributes = NSMutableArray()

      for index in 0..<numberOfColumns {
        let itemSize = self.itemsSize[index].CGSizeValue()
        let indexPath = NSIndexPath(forItem: index, inSection: section)
        let attributes = UICollectionViewLayoutAttributes(forCellWithIndexPath: indexPath)
        attributes.frame = CGRectIntegral(CGRectMake(xOffset, yOffset, itemSize.width, itemSize.height))

        if section == 0 && index == 0 {
          attributes.zIndex = 1024;
        } else  if section == 0 || index == 0 {
          attributes.zIndex = 1023
        }

        if section == 0 {
          var frame = attributes.frame
          frame.origin.y = self.collectionView!.contentOffset.y
          attributes.frame = frame
        }
        if index == 0 {
          var frame = attributes.frame
          frame.origin.x = self.collectionView!.contentOffset.x
          attributes.frame = frame
        }

        sectionAttributes.addObject(attributes)

        xOffset += itemSize.width
        column++

        if column == numberOfColumns {
          if xOffset > contentWidth {
            contentWidth = xOffset
          }

          column = 0
          xOffset = 0
          yOffset += itemSize.height
        }
      }
      if (self.itemAttributes == nil) {
        self.itemAttributes = NSMutableArray(capacity: self.collectionView!.numberOfSections())
      }
      self.itemAttributes .addObject(sectionAttributes)
    }

    let attributes : UICollectionViewLayoutAttributes = self.itemAttributes.lastObject?.lastObject as! UICollectionViewLayoutAttributes
    contentHeight = attributes.frame.origin.y + attributes.frame.size.height
    if( contentWidth == 0 || contentHeight == 0){return;}
    self.contentSize = CGSizeMake(contentWidth, contentHeight)
  }

  override func collectionViewContentSize() -> CGSize {
    if( self.contentSize != nil){
      return self.contentSize
    }else {
      return CGSizeMake(0, 0)
    }
  }

  override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> (UICollectionViewLayoutAttributes!) {
    return self.itemAttributes[indexPath.section][indexPath.row] as! UICollectionViewLayoutAttributes
  }

  override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
    var attributes = [UICollectionViewLayoutAttributes]()
    if self.itemAttributes != nil {
      for section in self.itemAttributes {

        let filteredArray  =  section.filteredArrayUsingPredicate(

          NSPredicate(block: { (evaluatedObject, bindings) -> Bool in
            return CGRectIntersectsRect(rect, evaluatedObject.frame)
          })
          ) as! [UICollectionViewLayoutAttributes]


        attributes.appendContentsOf(filteredArray)

      }
    }

    return attributes
  }

  override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
    return true
  }

  func sizeForItemWithColumnIndex(columnIndex: Int) -> CGSize {
    let text : String = "25.10.15"
    let size : CGSize = (text as NSString).sizeWithAttributes([NSFontAttributeName: UIFont.systemFontOfSize(17.0)])
    let width : CGFloat = size.width + 25
    return CGSizeMake(width, 30)
  }

  func calculateItemsSize() {
    self.itemsSize = NSMutableArray(capacity: numberOfColumns)
    for index in 0..<numberOfColumns {
      self.itemsSize.addObject(NSValue(CGSize: self.sizeForItemWithColumnIndex(index)))
    }
  }
}

The original library

Answer 1

The compiler doesn't know what is being returned by self.itemAttributes[indexPath.section] since its defined as an NSMutableArray. Instead you should define itemAttributes as an array of array of UICollectionViewLayoutAttributes which is what it looks like you've got. So itemAttributes: [[UICollectionViewLayoutAttributes]] should take care of that warning and would be the preferred way of writing that in Swift.

Edit: You should also redefine sectionAttributes as [UICollectionViewLayoutAttributes]. So now the compiler can fully infer the type of object being returned for the subscripting.

As for why it changed in the recent release, I'm not sure, I do not see anything about this specifically in the release notes.

Answer 2

Referring 'Peter Foti' answer , I have changed code to

let sectionAttributes = self.itemAttributes [indexPath.section] as! [UICollectionViewLayoutAttributes]
return sectionAttributes[indexPath.row] as UICollectionViewLayoutAttributes

Instead of line with error 'Ambiguous use of 'subscript'

return self.itemAttributes[indexPath.section][indexPath.row] as! UICollectionViewLayoutAttributes