UIFont extension for San Francisco system font style selection

systemFont.swift

extension UIFont {
    /// San Francisco System Font
    /// - Parameters:
    ///   - fontSize: Font size
    ///   - weight: Font weight (Optional, by default: weight is regular)
    ///   - design: Font design: default, rounded, monospaced, serif (Optional, by default: design is default)
    /// - Returns: System font of your size, weight and design
    static func systemFont(ofSize fontSize: CGFloat, weight: UIFont.Weight = .regular, design: UIFontDescriptor.SystemDesign = .default) -> UIFont {
        // Will be SF Compact or standard SF in case of failure.
        if let descriptor = UIFont.systemFont(ofSize: fontSize, weight: weight).fontDescriptor.withDesign(design) {
            return UIFont(descriptor: descriptor, size: fontSize)
        } else {
            return self.systemFont(ofSize: fontSize, weight: weight)
        }
    }
}

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.
    label.font = UIFont.systemFont(ofSize: 22.0, weight: .bold, design: .rounded)
}