Can I mix Swift with C++? Like the Objective-C .mm files

Question

I just changed my .m files to .mm and use C++. Is there a way to do the same with Swift?

Answer 1

The confusion may come from the assumption that merely changing a file extension from .m to .mm is all you need to bridge the languages, when, in reality, it does nothing of that sort. It is not the .mm that causes friction with .cpp, it is the .h header which must positively not be a C++ header.

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Same project: Yes.

In the same project, you can happily mix C, C++, Objective-C, Objective C++, Swift, and even Assembly.

1. ...Bridging-Header.h: you expose C, Objective-C and Objective-C++ to Swift using this bridge
2. <ProductModuleName>-Swift.h: exposes automatically your Swift classes marked with @objc to Objective-C
3. .h: this is the tricky part, since they are ambiguously used for all flavors of C, ++ or not, Objective or not. When a .h does not contain a single C++ keyword, like class, it can be added to the ...Bridging-Header.h, and will expose whatever function the corresponding .c or .cpp functionalities it declares. Otherwise, that header must be wrapped in either a pure C or Objective-C API.

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Same file: No.

In the same file, you can't mix all 5. In the same source file:

1. .swift: you can't mix Swift with anything
2. .m: you can mix Objective-C with C. (@Vinzzz)
3. .mm: you can mix Objective-C with C++. This bridge is Objective-C++. (@Vinzzz).
4. .c: pure C
5. .cpp: you can mix C++ & Assembly (@Vality)
6. .h: ubiquitous and ambiguous C, C++, Objective-C or Objective-C++, so the answer is it depends.

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References

• Invoke Assembly from C++ (Brett Hale)
• Invoke Swift from Objective-C (Svitlana)
• Invoke C, C++, Obj-C, Obj-C++ from Swift (SwiftArchitect, self)
• To download a full iOS 9, Xcode 7 project, search for SO-32541268 in Swift Recipes.