Most of the time you don't need to write @objc explicitly on a class—that's only if you care about its runtime name. If you do care about its runtime name, it seems like the same code wouldn't work on Linux.

Can you share the code where this is an issue? Collecting examples might help us decide what to do about it.

Here is the example codes:

@objc(STWUser)
public class User: NSObject {
    
    var jsonObject: [String:Any]
    
    @objc public var id: Int64
    @objc public var screenName: String
    @objc public var name: String? {
        return self.jsonObject["name"] as? String
    }
    @objc public var profileImageURL: URL? {
        return URL(string: self.jsonObject["profile_image_url"] as? String ?? "")
    }
    
    init?(jsonObject: Any) {
        guard let jsonObject = jsonObject as? [String:Any] else {
            return nil
        }
        self.jsonObject = jsonObject
        
        guard let id = jsonObject["id"] as? Int64 else {
            return nil
        }
        self.id = id
        
        guard let screenName = jsonObject["screen_name"] as? String else {
            return nil
        }
        self.screenName = screenName
        
        super.init()
    }
}

And I care the interface of obj-c line for working well with Obj-C. Meantime, without @objc, those codes are works well on Linux platform. I think @objc is only matters when Obj-C runtime is available. Isn't it?

Why do you need to rename the class to STWUser in Objective-C? Is this a library that's intended to be used in both Objective-C and Swift?

Yes. I want this library works well on both Obj-C, Swift.

Comment by Joe Charlier (JIRA)

I have a library that uses KVC and KVO that I'm trying to get working on Linux. This error is of course coming up on all String and Date properties. Is there anyway around this? Is KVC and KVO unavailable on linux swift?

aepryus (JIRA User): KVO, KVC is the features of Obj-C's Foundation which is not implemented in Linux. I suggest these for who build the framework targeting Linux, macOS both. (Which I intend to make swift ignore `@objc` annotation on Linux. Not makes the error.)

Comment by Joe Charlier (JIRA)

@sinoru: I actually need the KVC functionality in this case, so simply ignoring the warning without getting String and Date working with KVC won't be very helpful in my case.

I also came across this issue today. First of all, the error message is misleading. Given @objc class ABC: NSObject {{{}}} it's clearly visible that it does inherit from NSObject. No matter how @objc attributes are handled, the error message should currently state, that the ObjC runtime is not available on Linux.

Apart from that, I need the attribute in a test where we also care about the runtime name of the class. The tested logic involves NSStringFromClass which uses the @objc name on Darwin platforms. Currently, in our case it seems like the @objc attribute could just be ignored on Linux, since NSStringFromClass returns String(describing: cls) there.

Hi. I came across the same case as described in this issue – sharing code for iOS app and Swift backend. I managed to clean @objc annotations for backend-build using following script:

#!/bin/bash

DIR=$(dirname "${BASH_SOURCE[0]}")

find "${DIR}/../Sources" -name '*.swift' | while read SWIFT_FILE
do
  sed -i'' 's/@objc([^)]*)//g' "${SWIFT_FILE}"
  sed -i'' 's/@objc//g' "${SWIFT_FILE}"
done