a3-7.swift

private var cellViewModels: [PhotoListCellViewModel] = [PhotoListCellViewModel]() {
    didSet {
        self.reloadTableViewClosure?()
    }
}
var numberOfCells: Int {
    return cellViewModels.count
}
func getCellViewModel( at indexPath: IndexPath ) -> PhotoListCellViewModel

var isLoading: Bool = false {
    didSet {
        self.updateLoadingStatus?()
    }
}