How to add a border just on the top side of a UIView

I consider subclassing UIView and overriding drawRect overkill here. Why not add an extension on UIView and add border subviews?

@discardableResult
func addBorders(edges: UIRectEdge,
                color: UIColor,
                inset: CGFloat = 0.0,
                thickness: CGFloat = 1.0) -> [UIView] {

    var borders = [UIView]()

    @discardableResult
    func addBorder(formats: String...) -> UIView {
        let border = UIView(frame: .zero)
        border.backgroundColor = color
        border.translatesAutoresizingMaskIntoConstraints = false
        addSubview(border)
        addConstraints(formats.flatMap {
            NSLayoutConstraint.constraints(withVisualFormat: $0,
                                           options: [],
                                           metrics: ["inset": inset, "thickness": thickness],
                                           views: ["border": border]) })
        borders.append(border)
        return border
    }


    if edges.contains(.top) || edges.contains(.all) {
        addBorder(formats: "V:|-0-[border(==thickness)]", "H:|-inset-[border]-inset-|")
    }

    if edges.contains(.bottom) || edges.contains(.all) {
        addBorder(formats: "V:[border(==thickness)]-0-|", "H:|-inset-[border]-inset-|")
    }

    if edges.contains(.left) || edges.contains(.all) {
        addBorder(formats: "V:|-inset-[border]-inset-|", "H:|-0-[border(==thickness)]")
    }

    if edges.contains(.right) || edges.contains(.all) {
        addBorder(formats: "V:|-inset-[border]-inset-|", "H:[border(==thickness)]-0-|")
    }

    return borders
}

    // Usage:         
    view.addBorder(edges: [.all]) // All with default arguments 
    view.addBorder(edges: [.top], color: .green) // Just Top, green, default thickness
    view.addBorder(edges: [.left, .right, .bottom], color: .red, thickness: 3) // All except Top, red, thickness 3

With this code you’re not tied to your subclass too, you can apply it to anything and everything that inherits from UIView – reusable in your project, and any others. Pass in other arguments to your methods to define other colours and widths. Many options.