Overriding NS*** methods in Swift

Question

To provide a fallback language for NSLocalizedString, I'm using this #undef and #define in Objective-C:

#undef NSLocalizedString
#define NSLocalizedString(key, comment) @"NSLocalizedString has been replaced";

This works perfectly well if called from Objective-C, but if called from Swift, the new definition of NSLocalizedString is ignored. (bridging header is configured correctly and works)

Is this possible in Swift, and if so, how?

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Note: the real example is here on Github, also see SO answer here

Answer 1

You can do this for NSObject subclasses like this

extension NSObject {
    func NSLocalizedString(key: String, comment: String) -> String {
        return "yes we have localized an NSObject"
    }
}

What about AnyObject? In this case, you would have to be aware of and conform to the FallbackLanguage protocol in your AnyObject subclass

protocol FallbackLanguage: class {}

// add default implementations
extension FallbackLanguage {
    func NSLocalizedString(key: String, comment: String) -> String {
        return "yes we have localized AnyObject via FallbackLanguage protocol"
    }
}

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Notes

• These two solutions can both be in your project without any issues.
• If you're calling NSLocalizedString outside of a class instance, you're out of luck.