Swift globals and global functions in objective c

Question

the documentation says:

Global constants defined in C and Objective-C source files are automatically imported by the Swift compiler as Swift global

Answer 1

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];

Answer 2

Nice answer by @rintaro, but another alternative simple Swift answer for constants that can be used in both Swift and Objective-C:

@objcMembers
class MyConstants: NSObject {
    static let kMyConstant1 = "ConstantValue1";
    static let kMyConstant2 = "ConstantValue2";
    static let CARDS = ["card1", "card2"]
}

You can access this on both Swift and Objective-C by:

MyConstants.kMyConstant1 // this will return "ConstantValue1"
MyConstants.CARDS // this will return array ["card1", "card2"]