// Reducers
typealias Reducer<T> = (inout T) -> ()
func makeIncrement(by number: Int) -> Reducer<ViewController.State> {
    return { state in
        state.number += number
    }
}
// Initialization

let vc = ViewController(nibName: "ViewController", bundle: nil)
vc.incHandler = makeIncrement(by: 1)
vc.decHandler = makeIncrement(by: -1)

// VC
class ViewController: UIViewController {

    struct State {
        var number: Int
    }

    var state = State(number: 0) {
        didSet {
            render()
        }
    }

    @IBOutlet weak var numberLabel: UILabel!
    @IBOutlet weak var incButton: UIButton!
    @IBOutlet weak var decButton: UIButton!

    var incHandler: Reducer<State>!
    var decHandler: Reducer<State>!

    override func viewDidLoad() {
        super.viewDidLoad()
        render()
    }

    @IBAction func inc(_ sender: UIButton) {
        incHandler(&state)
    }

    @IBAction func dec(_ sender: UIButton) {
        decHandler(&state)
    }

    func render() {
        numberLabel.text = String(state.number)
    }
}