If you’re just starting out, you should work with released tools, which means Xcode 10.2.1, available from the Mac App Store. Pre-releases tools often have weird problems, and it’s best to avoid those where you can.
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Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1" + "@apple.com"
FWIW, I'm encountering the same error using Xcode 11.3.1. It's one of many problems I'm having trying to use C++ code in an iOS app project.
I've placed links in my last reply there and that put it into moderation. Not sure you can see it. People have succeeded in using C++ code but so far I am not among them.