Method cannot be marked @objc because its result type cannot be represented in Objective-C

Question

am exposing swift API's in Objective-C and the Objective-C runtime.

When i add "@objc" before the function throws an error "Method cannot be marked @objc because its result type cannot be represented in Objective-C"

My code is here

@objc public static func logIn(_ userId: String) -> User? { }

User is optional struct. how to solve this.

Answer 1

The key bit of information is this:

User is optional struct

If User is a struct, then it can't be represented in Objective-C, just the same as a Swift class that doesn't inherit from NSObject.

In order for the method logIn(_:) to be able to be marked @objc, then every type referenced in the method declaration has to be representable in Objective-C. You're getting the error message because User isn't.

To fix it, you're either going to have to change the declaration of User from this:

struct User {
    // ...
}

...to this:

class User: NSObject {
    // ...
}

...or redesign logIn(_:) so that it doesn't return a User.

---

You can find more information about this here. In particular, this answer offers the following potential solution:

The best thing i found was to wrap in a Box class

public class Box<T>: NSObject {
    let unbox: T
    init(_ value: T) {
        self.unbox = value
    }
}

Answer 2

Your class or protocol, must be inherited (extended) by NSObject or anyother class in its hierarchy, containing your code (function) with @objc notation.

Example:

class TestClass {
    public static func logIn(_ userId: String) -> User? { }
}

To use/declare @objc with this function, class must extend NSObject (or any other class in its hierarchy)

class TestClass {
    @objc public static func logIn(_ userId: String) -> User? { }
}

Update:

struct may not work with optional value in Objective-C, as a work around, you should change User from struct to class

Try following code and see:

public class User : NSObject {
    // Your code
}

public final class Manager : NSObject {

    @objc public static func logIn(_ userId: String) -> User? {
        return nil
    }
}

Here is snapshot with editor

Answer 3

Only an NSObject-derived class type can be seen by Objective-C. Use:

class User : NSObject {

}

Answer 4

Change the definition of your class as below

class User: NSObject {

}

In this way this class will be available in Objective-C