Xtykutl

Say I have some objc code:

typedef NSString * ObjcNSString;



@interface ObjC : NSObject

+ (void)doThingsWithString:(nullable ObjcNSString)mid;

@end

The corresponding generated Swift interface for the objc code above is:

public typealias ObjcNSString = NSString



open class ObjC : NSObject {

    open class func doThings(with mid: String?)

}

This is causing problem if I use the code in Swift:

let str: ObjcNSString? = nil

ObjC.doThings(with: str) // Cannot convert value of type 'ObjcNSString?' (aka 'Optional<NSString>') to expected argument type 'String?'

But I really want to use the ObjcNSString type in Swift, is there any way to make it work?

Just about everything in this question is a red herring. The only important thing about the error you're getting is the attempt to use an Optional<NSString> where an Optional<String> is expected. You can't do that. The matter has nothing to do with Objective-C; you can see for yourself in pure Swift:

    let s : NSString? = nil

    let s2 : String? = s // error

You seem to assume these two types, Optional<NSString> and Optional<String>, are somehow magically interchangeable. They are not.

But they are castable one to the other:

    let s : NSString? = nil

    let s2 : String? = s as String?

Thus you could solve your compile error by writing:

    let str: ObjcNSString? = nil

    ObjC.doThings(with: str as String?)

But I really want to use the ObjcNSString type in Swift

It's not quite clear what you can mean by that. It isn't a Swift type. It's an Objective-C type, and as an Objective-C type it is a synonym for NSString. Any place where NSString is expected by Objective-C, Swift will expect a String when using that API. Trying to substitute another name for NSString doesn't affect that fact.

Nor is it clear what your ultimate goals can be. You can pass a string from Swift where an ObjcNSString is expected by Objective-C, so what's the problem?

It looks like the code that was generated is not quite what you want.

The error you are getting is saying that your function is expecting a String type, but you are trying to use a ObjcNSString type.

To fix this, just change your function declaration to:

open class func doThings(with mid: ObjcNSString?)

But keep in mind, you can just use NSString in Swift. You don't need the typealias. You can just as well write your function like:

open class func doThings(with mid: NSString?)