collectionviewcontroller_1.swift

class CollectionViewController<Section, Item>: UIViewController, UICollectionViewDelegate
    where Section : Hashable & CaseIterable, Item : Hashable {
    
    // MARK: - Injections
    var layout: UICollectionViewLayout! = nil
    var snapshot : NSDiffableDataSourceSnapshot<Section, Item>! = nil
    var content: ((_ indexPath: IndexPath, _ item: Item) -> AnyView)! = nil
        
    var supplementaryKinds: [String]! = nil
    var supplementaryContent: ((_ kind: String, _ indexPath: IndexPath, _ item: Item?) -> AnyView)? = nil
    
    // MARK: - Properties
    private(set) var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
    private let diffQueue = DispatchQueue.global(qos: .background)
    
    // MARK: - Views
    lazy var collectionView: UICollectionView = {
        let collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: layout)
        collectionView.autoresizingMask = [.flexibleHeight, .flexibleWidth]
        collectionView.backgroundColor = .clear
        return collectionView
    }()

    // MARK: - Life Cycle
    override func viewDidLoad() {
        super.viewDidLoad()
        
        configureCollectionView()
        configureDataSource()
        
        // load initial data
        reloadDataSource(animating: false)
    }
}