class BaseViewController: UIViewController {

    let headerView: UIView = {
        let view = UIView()
        view.backgroundColor = UIColor.green
        return view
    }()

    func addHeader() {
        view.addSubview(headerView)
        // then anchor it to top
    }

}

class ScrollViewController: UIViewController {

    let scrollView: UIScrollView = {
        let view = UIScrollView()
        view.backgroundColor = UIColor.green
        return view
    }()

    func addScrollView() {
        view.addSubview(scrollView)
        // then anchor it to top
    }

}

class HomeViewController: ScrollViewController, BaseViewController {

    override viewDidLoad() {
        super.viewDidLoad()

        addScrollView()
        addHeaderView()

        let view = UIView()
        //anchor view to bottom of the header
    }
}

protocol HeaderProtocol {
    func addHeader()
}

extension HeaderProtocol where Self: UIViewController {
    func addHeader() {
        let headerView = UIView()
        headerView.backgroundColor = UIColor.green
        view.addSubview(headerView)
        // then anchor it to top
    }
}

protocol ScrollViewProtocol {
    func addScrollView()
}

extension ScrollViewProtocol where Self: UIViewController {
    func addScrollView() {
        let scrollView = UIScrollView()
        scrollView.backgroundColor = UIColor.green
        view.addSubview(scrollView)
        // then anchor it to top
    }
}

class HomeViewController: ScrollViewProtocol, HeaderProtocol {
    override func viewDidLoad() {
        super.viewDidLoad()

        addScrollView()
        addHeaderView()
    }
}