This project's still on Swift 3, so I don't have first-hand experience upgrading to Swift 4. It looks like there are breaking changes though, albeit not nearly

This project's still on Swift 3, so I don't have first-hand experience upgrading to Swift 4. It looks like there are breaking changes though, albeit not nearly as many as 3 had. The most notable one looks like in the String API [1]. There are a few other minor ones that most projects won't hit, like in the dictionary/set API [2]. A few of these are also slightly more breaking than it initially seems because they've added temporary compatibility workarounds marked as deprecated in Swift 4 to avoid breaking as much working Swift 3 code, but these will go away for Swift 5, so you do still have to port anyway (just not immediately). [1] https://github.com/apple/swift-evolution/blob/master/proposals/0163-string-revision-1.md#source-compatibility https://github.com/apple/swift-evolution/blob/master/proposa... [2] https://github.com/apple/swift-evolution/blob/master/proposals/0165-dict.md#source-compatibility https://github.com/apple/swift-evolution/blob/master/proposa...