collectionview begin/end coredata updates

collectionview-beginend-updates.swift

import Foundation
import UIKit
import CoreData

class PresentationsListVC: UIViewController {
    @IBOutlet weak var collectionView: UICollectionView?
    
    // UICollectionView doesn't do beginUpdates/endUpdates.
    // CoreData modifications are stored in here and performed together
    var collectionViewItemChanges = [CollectionViewChange]()
    
    var fetchedResultsController: NSFetchedResultsController?
    
    var model: Model? { didSet { initializeFetchedResultsController() } }
    
    override func viewDidAppear(animated: Bool) {
        tagScreen(_stdlib_getDemangledTypeName(self))
        
        customizeViewAppearance()
    }

    func customizeViewAppearance() {
    }
}


// MARK: NSFetchedResultsController and Delegate

extension PresentationsListVC: NSFetchedResultsControllerDelegate {
    
    func initializeFetchedResultsController() {
        
        if let model = model {
            let controller = model.fetchedResultsController("Presentation",
                sortDescriptors: [NSSortDescriptor(key: "createdDate", ascending: false)]
            )
            
            var error: NSError?
            if !controller.performFetch(&error) {
                println("*** ERROR: Cannot perform fetch \(controller) \(error)")
            }
            
            controller.delegate = self
            fetchedResultsController = controller
            
            collectionView?.reloadData()
        }
    }
    
    func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {
        collectionViewItemChanges.append([type: [indexPath, newIndexPath]])
    }
    
    func controllerDidChangeContent(controller: NSFetchedResultsController) {
        collectionView?.performBatchUpdates({ self.collectionViewItemChanges.map {self.performCollectionViewChange($0)} }, completion: nil)
    }
    
    func performCollectionViewChange(change: CollectionViewChange) {
        let type = change.keys.array.first!
        let indexPaths = change[type] as! [NSIndexPath]
        
        switch change.keys.array.first! {
        case .Insert:
            collectionView?.insertItemsAtIndexPaths(indexPaths)
        case .Update:
            collectionView?.reloadItemsAtIndexPaths(indexPaths)
        case .Move:
            collectionView?.moveItemAtIndexPath(indexPaths[0], toIndexPath: indexPaths[1])
        case .Delete:
            collectionView?.deleteItemsAtIndexPaths(indexPaths)
        }
    }
}


// MARK: Collection view delegate

extension PresentationsListVC: UICollectionViewDelegate, UICollectionViewDataSource {
    
    func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
        return 1
    }
    
    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return fetchedResultsController?.sections?[section].numberOfObjects ?? 0
    }
    
    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        if let item = fetchedResultsController?.objectAtIndexPath(indexPath) as? Presentation {
            let cell = collectionView.dequeueReusableCellWithReuseIdentifier("PresentationsVCCell", forIndexPath: indexPath) as! UICollectionViewCell
            
            let imageView = UIImageView(image: UIImage(named: "login-logo"))
            cell.contentView.addSubview(imageView)
            
            return cell
        }
        
        return UICollectionViewCell()
    }
}

I am not getting what is declaration for CollectionViewChange( in line 11). Please provide details for CollectionViewChange