How do I specify the type of the next parameter based on the type of the previous parameter? [duplicate]

Question

I have an interface like

type messageType = 'msg' | 'peerCommon'
type peerCommonMessageType = 'hangUp' | 'disconnect' | 'inviteReject' | 'partyReject'
interface reciveMessage {
    type: messageType
    message: string | peerCommonMessageType
}

I want the type of message to be string when the Type is msg, and the type of message to be peerCommonMessageType when the Type is peerCommon, how do I modify the above code?

Answer 1

Use a discriminated union:

type messageType = 'msg' | 'peerCommon'
type peerCommonMessageType = 'hangUp' | 'disconnect' | 'inviteReject' | 'partyReject'

interface msgMessage {
    type: 'msg';
    message: string;
}

interface peerCommonMessage {
    type: 'peerCommon'
    message: peerCommonMessageType
}

type reciveMessage = msgMessage | peerCommonMessage;

// Passes
const test1: reciveMessage = {
    type: 'msg',
    message: 'any string'
}

// Fails
const test2: reciveMessage = {
    type: 'peerCommon',
    message: 'any string'
}

// Passes
const test3: reciveMessage = {
    type: 'peerCommon',
    message: 'hangUp'
}

Answer 2

I handled the same thing. Try this on MainVC:

 class MainVC: UIViewController, SecondVCDelegate {
    func passData(text: String) {
        // do stuff
    }
    @IBAction func openNextVC(_ sender: Any) {
        guard let secondController = self.storyboard?.instantiateViewController(withIdentifier: "AddGroupVC") as? AddGroupVC else { return }
        secondController.delegate = { [weak self] in
              print("call your delegates here")
                    
          }
      self.navigationController?.present(secondController, animated: true, completion: nil)
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
}

On second View Controller, call the delegates in viewWillDisappear :

class SecondVC: UIViewController {
        var delegate: SecondVCDelegate?
    
        @IBAction func save(_ sender: Any) {
           // do stuff
      self.dismiss(animated: true, completion: nil)
        }
        override func viewDidLoad() {
            super.viewDidLoad()
        }
 override func viewWillDisappear(_ animated: Bool) {
        
        self.delegate
        
    }
    }