Application's fonts protocol for easy and convenient fonts makeup use

FontFamily+Roboto.swift

import Foundation

enum Roboto: String, FontFamily {
    case thin    = "Roboto-Thin"
    case bold    = "Roboto-Bold"
    case light   = "Roboto-Light"
    case medium  = "Roboto-Medium"
    case regular = "Roboto-Regular"
}

FontFamily.swift

import Foundation

// MARK: - Application's fonts protocol
protocol FontFamily {
    
    var fontName: String { get }
}

// MARK: - FontFamily Protocol default implementation
extension FontFamily where Self: RawRepresentable, Self.RawValue == String {
    
    var fontName: String {
        return rawValue
    }
}

// MARK: - UIFont extension for application's UI fonts
extension UIFont {
    
    // Common font sizes in application 
    enum Size: CGFloat {
        case small  = 10
        case lite   = 12
        case medium = 14
        case normal = 16
        case big    = 20
        case extra  = 24
    }
    
    convenience init?(_ fontFamily: FontFamily, size: UIFont.Size) {
        self.init(name: fontFamily.fontName, size: size.rawValue)
    }
    
    convenience init?(_ fontFamily: FontFamily, size: CGFloat) {
        self.init(name: fontFamily.fontName, size: size)
    }
}

Example:

let _ = UIFont(Roboto.bold, size: .normal)
let _ = UIFont(Roboto.bold, size: 56.0)