Using @import in objective C in conjunction with __cplusplus

Question

When I try to compile an Objective C++ file (.mm) that is linked to a file that uses the new @import directive, I get some errors. Currently, my only solution is to replace

Answer 1

Edit: According to the latest docs this should work now.

See this. You have to use the -fcxx-modules flag instead of the -fmodules flag, but as the official documentation suggests - EXPERIMENTAL and VERY BROKEN. I didn't manage to get it working at all... In my opinion it's better to stick with #import and #include until that feature is out of experimental stage.

From clang.llvm.org:

-fcxx-modules
    Enable the modules feature for C++ (EXPERIMENTAL and VERY BROKEN).

Answer 2

In my case I needed to use OpenCV in my application.

I have solved this problem by adding

-fcxx-modules (Objective C++) manually to "Other C++ Flags"

(Build Settings/ Apple Clang - Custom Compiler Flags/ Other C++ Flags)

or

-fmodules (Objective C) to "Other C Flags"

(Build Settings/ Apple Clang - Custom Compiler Flags/ Other C Flags)

And also I needed to put import the opencv.hpp before any Apple's headers to fix errors of Expected identifier in opencv library. For example in Prefix.pch I organized it that way:

#ifdef __cplusplus
#include <opencv2/opencv.hpp>
#endif

#import <Availability.h> 

I am using:

• Xcode - 11.3
• CocoaPods - 1.9.1
• OpenCV2 - 4.3.0