let gradientView = GradientView(colors: [.red, .blue, .black])
gradientView.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(gradientView)
gradientView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
gradientView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
gradientView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
gradientView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true

UIView.animate(withDuration: 5) {
    gradientView.angle = .radians(.pi)
}

gradientView.angleDidUpdateHook = {
    print($0.degrees)
}