[Animate border of UIView by protocol implementation]

animateBorderWithConformingToProtocol.swift

protocol PLAnimatableBorder {
    func animateBorderWidth(toValue: CGFloat, duration: Double)
}

extension PLAnimatableBorder where Self: UIView {
    /// animate the border width
    func animateBorderWidth(toValue: CGFloat, duration: Double) {
        let animation: CABasicAnimation = CABasicAnimation(keyPath: "borderWidth")
        animation.fromValue = layer.borderWidth
        animation.toValue = toValue
        animation.duration = duration
        layer.add(animation, forKey: "Width")
        layer.borderWidth = toValue
    }
}