DataSource.swift

class ViewController: UIViewController {
    @IBOutlet var collectionview: UICollectionView!
    lazy var dataSource = UICollectionViewDiffableDataSource<Section, Item>(collectionView: self.collectionview,
                                                                            cellProvider: self.cellProvider)
    lazy var cellProvider: (UICollectionView, IndexPath, Item) -> UICollectionViewCell? = { collectionView, indexPath, item in
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath)
        cell.backgroundColor = item.color
        return cell
    }
    
    override func viewDidLoad() {
       super.viewDidLoad()
    }
}