'filenames are used to distinguish private declarations of the same name' error

Question

I am getting this error on generating an NSManagedObject in Xcode 8.1 in Swift.

:0: error: filename "DemoOne+CoreDataClass.swift" used twice: '/Users/Swasidhant/Desktop/demo again/DemoOne+CoreDataClass.swift' and '/Users/Swasidhant/Library/Developer/Xcode/DerivedData/demo_again-hiinrbwwbmyfbrbctsfdzvudkkuy/Build/Intermediates/demo again.build/Debug-iphonesimulator/demo again.build/DerivedSources/CoreDataGenerated/Model/DemoOne+CoreDataClass.swift' :0: note: filenames are used to distinguish private declarations with the same name :0: error: filename "DemoOne+CoreDataProperties.swift" used twice: '/Users/Swasidhant/Desktop/demo again/DemoOne+CoreDataProperties.swift' and '/Users/Swasidhant/Library/Developer/Xcode/DerivedData/demo_again-hiinrbwwbmyfbrbctsfdzvudkkuy/Build/Intermediates/demo again.build/Debug-iphonesimulator/demo again.build/DerivedSources/CoreDataGenerated/Model/DemoOne+CoreDataProperties.swift' :0: note: filenames are used to distinguish private declarations with the same name Command /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc failed with exit code 1

I searched for this and got answers saying the file might be present twice in the project which is not my case. Another solution I came across was to remove the file from the build phase and add again. That too didn't work. Is it some build setting configuration mistake ? Or something else?

Here is the link with a demo project created with Xcode 8.1 and showing this problem:- https://www.dropbox.com/s/xwyzhshktb2hqe7/demo2.zip?dl=0

Answer 1

The issue is happening because of the Xcode automatic subclass generation feature.

According to What's New In Core Data

Xcode automatic subclass generation

Xcode now supports automatic generation of NSManagedObject subclasses in the modeling tool. In the entity inspector:

• Manual/None is the default, and previous behavior; in this case you should implement your own subclass or use NSManagedObject.
• Category/Extension generates a class extension in a file named like ClassName+CoreDataGeneratedProperties. You need to declare/implement the main class (if in Obj-C, via a header the extension can import named ClassName.h).
• Class Definition generates subclass files named like ClassName+CoreDataClass as well as the files generated for Category/Extension.

The generated files are placed in DerivedData and rebuilt on the first build after the model is saved. They are also indexed by Xcode, so command-clicking on references and fast-opening by filename works.

So for fixing your issue, you need to set the Codegen field value to Manual/None as shown below: