An example of a back port implementation to facilitate backward compatibility handling in Swift.

CleanBackwardCompatibility.swift

//
//  Demo.swift
//  bedtimefanlite
//
//  Created by Sofia Chevrolat on 02/11/2021.
//  Inspired by [Dave DeLong's post](https://davedelong.com/blog/2021/10/09/simplifying-backwards-compatibility-in-swift/)
//
// Two small examples of a "backport" implementation to facilitate backward compatibility.
//
// USAGE :
// 1 - extend the type by adding an enum named `Backport`
// 2 - add an enum case matching exactly the signature of the "backported" function
// 3 - add a computed variable in the enum to return the needed value, encapsulating the `if #available` calls.
// 4 - When you're ready to drop support for the older iOS version, remove the relevant enum case.
//      The compiler will tell you where to correct the code. You can simply remove the `.Backport.` and the `.variable`
//      to get the correct function.

import Foundation
import UIKit

class DemoFontBackPortComplete {
    let fontSize: CGFloat = 64
    let label = UILabel()

    init() {
        label.font = UIFont.Backport.monospacedSystemFont(ofSize: fontSize, weight: .regular).font
    }
}

class DemoSFBackPortComplete {
    let image: UIImage?

    init() {
        image = UIImage.Backport.`init`(systemName: "some_SF_symbol").image
    }
}

// MARK: - Backports (could be placed in a single file)

extension UIFont {
    enum Backport {
        // case with identical signature to the "backported" function
        case monospacedSystemFont(ofSize: CGFloat, weight: UIFont.Weight)
        // a variable to return the needed value
        var font: UIFont {
            switch self {
                case .monospacedSystemFont(let fontSize, let fontWeight):
                    if #available(iOS 13.0, *) {
                        return UIFont.monospacedSystemFont(ofSize: fontSize, weight: fontWeight)
                    } else {
                        return UIFont.monospacedDigitSystemFont(ofSize: fontSize, weight: fontWeight)
                    }
            }
        }
    }
}

extension UIImage {
    enum Backport {
        case `init`(systemName: String)
        var image: UIImage? {
            switch self {
                case .`init`(let assetName):
                    if #available(iOS 13.0, *) {
                        return UIImage(systemName: assetName)
                    } else {
                        return UIImage(named: assetName)
                    }
            }
        }
    }
}