Call a Swift Singleton from Objective-C

Question

I'm having some trouble accessing a Swift Singleton from Objective-C.

@objc class SingletonTest: NSObject {

    // swiftSharedInstance is not accessible from ObjC
    class var swiftSharedInstance: SingletonTest {
    struct Singleton {
        static let instance = SingletonTest()
        }
        return Singleton.instance
    }        
}

swiftSharedInstance can not be reached.

Answer 1

Nicky Goethlis's answer is correct but I just want to add another way of Singleton creation termed as One line Singleton" in Swift which I came across recently and it does not use Struct:

Singleton.swift

@objc class Singleton: NSObject {

  static let _singletonInstance = Singleton()
  private override init() {
    //This prevents others from using the default '()' initializer for this class.
  }

  // the sharedInstance class method can be reached from ObjC. (From OP's answer.)
  class func sharedInstance() -> Singleton {
    return Singleton._singletonInstance
  }

  // Some testing
  func testTheSingleton() -> String {
    return "Hello World"
  }
}

SomeObjCFile.m

Singleton *singleton = [Singleton sharedInstance];
NSString *testing = [singleton testTheSingleton];
NSLog(@"Testing---> %@",testing);

Answer 2

Swift 5 and above

final class Singleton: NSObject {

    @objc static let shared = Singleton()

    @objc var string: String = "Hello World"

    private override init() {}   
}

use in Objective-C

NSLog("Singleton String = %@", [Singleton shared].string]);