这应该大致将上述Objective-C转换为Swift：

This should roughly translate the above Objective-C to Swift:

if (Twitter.sharedInstance().session() != nil) {
        if let shareEmailViewController = TWTRShareEmailViewController(completion: {
            (email: String!, error: NSError!) in
            if (email != nil) {
                print("\(email)")
            } else {
                print("\(error)")
            }
        }) {
            self.presentViewController(shareEmailViewController, animated: true, completion: nil)
        }
    } else {
        print("User not logged in")
    }