After downloading Xcode 6 beta 6, If you are receiving Apple Mach-O Linker error, Undefined symbols for architecture then try clearing the DerivedData for Xcode.

Undefined symbols for architecture x86_64:

“__TFSs26_forceBridgeFromObjectiveCU__FTPSs9AnyObject_MQ__Q_”, referenced from:

Derived data folder location

You find out the location of derived data using Xcode Preferences. Click Xcode -> Preferences.

Click Locations tab and navigate to Derived Data section. Then click the arrow next to folder the path.

Now delete DerivedData folder under Xcode.

Useful link – http://stackoverflow.com/questions/25371556/swift-beta-6-confusing-linker-error-message