Ambiguous reference to member Swift 3

I got the same error Ambiguous reference to member with the same method on converting it from Swift 4 to Swift 5. Looks like the completion handler has been changed to support the new Result type. Changing the completing handler to below fixed the issue for me,

        oauthVarSwift.authorize( withCallbackURL: URL(string: "")!,
                             scope: "", state:"", completionHandler: {  result in
                                switch result {
                                case .success(let credential, let response,  let parameters):
                                    print(credential.oauthToken)

                                case .failure(let error):
                                 print(error)
                                }

          })

I think the problem is caused by some shortcomings of Swift's type inference in combination with closures. You could try one of the following:

Either don't use trailing closures, e.g.

oauthswift.authorize(withCallbackURL: URL(string: info.callBackUrl)!, scope: info.scope, state: info.state, success: { (credential, response, parameters) in

         successHandler(credential, response, parameters)
}, failure: { (error) in

    failure(error: error)
    print(error.localizedDescription)
})

or provide an explicit type for error, e.g.

 oauthswift.authorize(withCallbackURL: URL(string: info.callBackUrl)!, scope: info.scope, state: info.state, success: { (credential, response, parameters) in

         successHandler(credential, response, parameters)
 }) { (error: Error) in

     failure(error: error)
     print(error.localizedDescription)
 }

For reference: This kind of error appears when there's more than one variable/method with the same name, does your oauthswift has more than one "thing" called "authorize"? like another method? My error was that i declared:

let fileManager = FileManager()

and in

let _ = try localFileManager.createDirectory(...) 

I got the same error, changing the variable name in localFileManager fixed it.