Custom dynamic type

UIFont+CustomDynamicType.swift

public extension UIFont {
    
    static func loadGothamNarrow(ofSize size: CGFloat, weight: UIFont.Weight) -> UIFont {
        let name: String = {
            switch weight {
            case .bold, .black, .heavy, .semibold:
                return "GothamNarrow-Bold"
            default:
                return "GothamNarrow-Book"
            }
        }()
        return UIFont(name: name, size: size) ?? systemFont(ofSize: size, weight: weight)
    }

    public static func font(for style: TextStyle, weight: Weight, fontFace: FontFace = .system) -> UIFont {
        let desc = UIFontDescriptor.preferredFontDescriptor(withTextStyle: style)
        let font: UIFont = {
            switch fontFace {
            case .system:
                return systemFont(ofSize: desc.pointSize, weight: weight)
            case .gothamNarrow:
                return loadGothamNarrow(ofSize: desc.pointSize, weight: weight)
            }
        }()
        return UIFontMetrics(forTextStyle: style).scaledFont(for: font)
    }
    
    public enum FontFace {
        case system
        case gothamNarrow
    }
    
    // Convenience properties for standardization
    
    public static var titleMedium: UIFont { font(for: .title2, weight: .bold, fontFace: .gothamNarrow) }
}

public extension UILabel {
    public func set(font: UIFont) {
        self.font = font
        adjustsFontForContentSizeCategory = true
    }
}

Call site usage is nice and clean on a label:

titleLabel.set(font: .titleMedium)