Module compiled with swift 4.0 cannot be imported in swift 3.1

Question

Apparently I have managed to build my project in Xcode 9 beta and now I only get the error

Module compiled with swift 4.0 cannot be imported in swift 3.1<

Answer 1

Same problem here but using Carthage. And here is the answer:

• rm -rf ~/Library/Caches/org.carthage.CarthageKit/DerivedData
• delete the Carthage folder for the project
• Update Carthage: carthage update --platform iOS

And voilà!