Preparation before migration

Ensure that the project that you are migrating builds successfully in Swift 3.2 mode, and all its tests pass. Keep in mind that Swift 3.2 does have significant changes from 3.1 as well as the SDKs against which you built, so you may need to resolve errors initially.

It’s highly recommended that you manage your project under source control. This enables you to easily review the applied changes via the migration assistant, get rid of them, and retry the migration if required.

Different from last year, the migrator is built directly into the compiler and not a separate tool, so it can work with both the versions of Swift, that is, 3.2, and 4.