I was about to purchase iOS Apprentice that covers XCode9 / Swift 4.0.
Would it be better to hold off for a possible newer release covering Swift 4.2 / Xcode 10 or will the PDF/ePub version of the current book include those changes via an update?
(Happy to wait if there’s a newer version on the horizon).
I believe when you purchase the PDF/ePub version, you get updates free of charge. So it should not matter whether you purchase the book now or later
That said, the book will be updated for Xcode 10 / Swift 4.2 / iOS 12. Generally, an update to the book will appear soon after the matching iOS version is released by Apple.