Since the code works with Xcode 10 and Swift 4.2, there should not be any properties that are deprecated and not available to Swift. So my suspicion is that you had defined iconImage as a different type than what the book specifies. Can you check the type of the iconImage property against the code provided in the book?
If it doesn’t match, that’s your issue …
If it matches then, one thing you can do is check your project against the provided final project in the book if you want to troubleshoot the issue yourself.
Alternatively, please upload your project as a ZIP file somewhere and provide a link to the ZIP file so that I (or someone else) can download the file and see what might be going on.
I checked my ListDetailViewController.swift against the ListDetailViewController.swift provided in the final project in the book. It turns out I made a mistake of defining iconImage as UITableViewCell instead of UIImageView!
After making the necessary changes, I built the app with no errors. I have made a callous mistake.
I’m glad that you were able to sort it out And don’t worry about the mistakes - they happen to even the most experienced programmer. The thing is to learn from each mistake as to how to spot what might be going wrong …