Swiftify does not include a converter between different Swift versions because such a converter exists in Xcode.
To migrate to a newer version from Xcode, choose Edit -> Convert -> To Current Swift Syntax from the Xcode menu.
Depending on your source code's Swift version, you might need a different Xcode version for the conversion:
- Swift 1 -> 2, Xcode 7
- Swift 2 -> 3, Xcode 8
- Swift 3 -> 4, Xcode 9
- Swift 3 or 4 -> 4.2, Xcode 10
To get an earlier version of Xcode, you can use your Apple Developer Account to download it from the developer portal: https://developer.apple.com/download/
For more information on migrating to Swift 4.2, check Swift’s official blog at Swift.org - Migrating to Swift 4.2 where you can also find migration guides for earlier versions of Swift.