Overview of layout for https://github.com/yfujiki/CompositionalLayoutSample

CompositionalLayoutSample-Overview.swift

private lazy var compositionalLayout: UICollectionViewCompositionalLayout = {
    let layout = UICollectionViewCompositionalLayout { [weak self]
        (sectionIndex: Int, layoutEnvironment: NSCollectionLayoutEnvironment) -> NSCollectionLayoutSection? in
        switch Section(rawValue: sectionIndex) {
        case .brandNames:
            return self?.setupBrandNamesSection()
        case .catFoods:
            return self?.setupCatFoodsSection()
        case .cats:
            return self?.setupCatsSection()
        case .none:
            fatalError("Should not be none ")
        }
    }
    return layout
}()

override func viewDidLoad() {
    super.viewDidLoad()

...
    collectionView.collectionViewLayout = compositionalLayout
...
}