Traceable.swift

//: A UIKit based Playground to present user interface
  
import UIKit
import PlaygroundSupport

protocol Traceable {
    var cornerRadius: CGFloat { get set }
    var borderColor: UIColor? { get set }
    var borderWidth: CGFloat { get set }
    
    func addDefaultBorder()
}

extension Traceable where Self: UIView {
    var cornerRadius: CGFloat {
        get { return layer.cornerRadius }
        set {
            layer.masksToBounds = true
            layer.cornerRadius = newValue
        }
    }
    
    var borderColor: UIColor? {
        get {
            guard let cgColor = layer.borderColor else { return nil }
            return  UIColor(cgColor: cgColor)
        }
        set { layer.borderColor = newValue?.cgColor }
    }
    
    var borderWidth: CGFloat {
        get { return layer.borderWidth }
        set { layer.borderWidth = newValue }
    }
    
    func addDefaultBorder() {
        layer.masksToBounds = true
        layer.cornerRadius = 20
        layer.borderWidth = 2
        layer.borderColor = UIColor.red.cgColor
    }
}

extension UIImageView: Traceable {}
extension UIButton: Traceable {}

let view = UIView()
view.frame = CGRect(x: 0, y: 0, width: 280, height: 280)

let imageView = UIImageView()
imageView.backgroundColor = .green
imageView.frame = CGRect(x: 65, y: 65, width: 150, height: 150)
imageView.addDefaultBorder()
view.addSubview(imageView)

let button = UIButton()
button.backgroundColor = .blue
button.addDefaultBorder()
button.frame = CGRect(x: 00, y: 240, width: 280, height: 40)
view.addSubview(button)

PlaygroundPage.current.liveView = view