Swift globals and global functions in objective c

Here is the document about it

You’ll have access to anything within a class or protocol that’s
marked with the @objc attribute as long as it’s compatible with
Objective-C. This excludes Swift-only features such as those listed
here:

• Generics
• Tuples
• Enumerations defined in Swift
• Structures defined in Swift
• Top-level functions defined in Swift
• Global variables defined in Swift
• Typealiases defined in Swift
• Swift-style variadics
• Nested types
• Curried functions

Global variables (including constants) are unaccessible from Objective-C.

Instead, you have to declare a class which has accessors for the global constants.

// Swift
public let CARDS = ["card1", "card2"]

@objc class AppConstant {
   private init() {}
   class func cards() -> [String] { return CARDS }
}

// Objective-C
NSArray *cards = [AppConstant cards];