If you follow Quinn's steps as written, you'll see that it (eventually) builds and runs as described. As Quinn says, "Test768928-Swift.h is managed by Xcode" — more precisely, it is created by Xcode and populated when you build the project, but it's not added to your project and you don't normally interact with it. (If you really want to see it, open the build folder with Product > Show Build Folder in Finder, and then from there, go to Intermediates.noindex > Test768928.build > Debug > Test768928.build > DerivedSources; you'll find it in there. There's about 650 lines of boilerplate, and then down at the bottom you'll find namespace Test768928 and the code that implements MySwiftClass::init() in C++.)