How can I hide part of an Objective-C class's interface from Swift?

Question

I have an Xcode project that is a mix of Objective-C(++), C++, and Swift. Some of the Objective-C++ serves as a bridge between Swift and C++.

Say I have an Objective-C class with a public property whose type is a C++ class that I want to use from other parts of the Objective-C code. This will cause a compiler error if the header is imported in the Swift bridging header. Is there a way to hide part of the header of this Objective-C class from Swift?

EDIT: here's a sample header file to illustrate what I mean.

#import <Foundation/Foundation.h>

class MyCppType;

@interface SwiftCancelationToken : NSObject

//I need to expose this so Obj-C can interact with it
@property MyCppType *cppProperty;

-(void)doSomethingWithCppObject;

@end

Maybe, but from my own (limited) working with Objective-C and Objective-C++ and Swift: no. (But as said, "maybe", I may be wrong.) — Eljay
– Eljay, Commented Mar 15, 2023 at 0:23
NS_SWIFT_UNAVAILABLE? developer.apple.com/documentation/swift/… — Rob
– Rob, Commented Mar 15, 2023 at 0:57
@Rob NS_SWIFT_UNAVAILABLE may work for hiding properties and methods, but I have to expose my C++ object as a property on the wrapper object, which means either forward-declaring its type or importing its header, both of which cause a compiler error. See the edit to the question. — Tom Hamming
– Tom Hamming, Commented Mar 15, 2023 at 16:49

Aleksandr Medvedev · Accepted Answer · 2023-03-15 18:32:11Z

2

Long story short - this is a mistake in the class API design. If you want to have a header compatible with Objective-C/Swift, it cannot expose any C++ stuff, such as C++ classes, templates, keywords, etc... There is only Swift - Objective-C interoperability (and sometimes C), but not Swift - Objective-C++ interoperability (there is however Swift - C++ interop project ongoing).

On the other hand, you can technically put pre-processor, which may omit any C++ parts from the header, when the compiler-frontend is in another language mode with use of __cpluplus guards:

#import <Foundation/Foundation.h>

#ifdef __cplusplus
class MyCppType;
#endif

@interface SwiftCancelationToken : NSObject

#ifdef __cplusplus
@property MyCppType *cppProperty;
#endif

-(void)doSomethingWithCppObject;

@end

edited Mar 15, 2023 at 18:32

answered Mar 15, 2023 at 17:04

Aleksandr Medvedev

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