Xcode 8 Objective-C category warning

Question

I\'m using Xcode 8 and Swift 3.0. What does this error message mean?

ld: warning: Some object files have incompatible Objective-C category definition

Answer 1

In my case it was a class variable.

public extension NSObject {
    public class var nameOfClass: String{
        return NSStringFromClass(self).components(separatedBy: ".").last!
    }

Adding @nonobjc helped.