@IBDesignable
class ViewController: UIViewController {
    #if TARGET_INTERFACE_BUILDER
    @IBInspectable
    var topLeft: Bool = false {
        didSet {
            updateCornerMask()
        }
    }

    @IBInspectable
    var topRight: Bool = false {
        didSet {
            updateCornerMask()
        }
    }

    @IBInspectable
    var bottomLeft: Bool = false {
        didSet {
            updateCornerMask()
        }
    }

    @IBInspectable
    var bottomRight: Bool = false {
        didSet {
            updateCornerMask()
        }
    }

    func updateCornerMask() {
        cornerMask = CACornerMask(
            TL: topLeft,
            TR: topRight,
            BL: bottomLeft,
            BR: bottomRight)
    }
    #endif

    var cornerMask: CACornerMask?
}

extension CACornerMask {
    init(TL: Bool = false, TR: Bool = false, BL: Bool = false, BR: Bool = false) {
        var value: UInt = 0
        if TL { value += 1 }
        if TR { value += 2 }
        if BL { value += 4 }
        if BR { value += 8 }

        self.init(rawValue: value)
    }
}