Return value for function in nested function (Swift 3 | Xcode)

Question

I'm trying to return a value for a function from inside of a nested function. I understand why it doesn't work, but I just need to know a workaround for my type of problem.

In my code, I'm checking whether or not a person has already been created inside of my Firebase Database. So inside of the usersRef function, you'll see that if the value return from firebase is "nil" then the user hasn't been created and vice versa.

When I say : return userBool it's giving me this error:

Unexpected non-void return value in void function

Been looking for a clean workaround, but the only thing I can think of is having to create this function over and over again for each of the various times I want to check it. Obviously, I'd rather not do that, haha, so if you could help me out by giving some suggestions on how to fix this and have a clean solution, let me know! :)

func checkIfUserExists(userID : String) -> Bool {
    var userBool = Bool()
    var usersRef = FIRDatabase.database().reference()
    usersRef.child("users").child(userID).observeSingleEvent(of: .value, with: {
    snapshot in
        if snapshot.value != nil {
            userBool = true
            return userBool
        }
        else {
            userBool = false
            return userBool
        }
    })
}

UPDATE :

Thanks to your suggestions, I added a completion, and it worked perfectly. :)

func checkIfUserExists(userID : String, completion: @escaping (_ success: Bool) -> ()){
    var userBool = Bool()
    var usersRef = FIRDatabase.database().reference()
    usersRef.child("users").child(userID).observeSingleEvent(of: .value, with:{
        snapshot in
            if snapshot.value != nil {
                print("userBool!", userBool)
                userBool = true
            }
            else {
                print("userBool2!", userBool)
                userBool = false
            }
        completion(userBool)
    })
}

Moritz Lang · Accepted Answer · 2017-01-18 21:01:18Z

2

There is no way to return from the outer function from within the inner one. The only way I can think of is by using a completion handler, that you can then call from within the nested function like so:

func checkIfUserExists(userID : String, completion: @escaping (_ userExists: Bool) -> Void)

answered Jan 18, 2017 at 21:01

Moritz Lang

362 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Jared Davidson Over a year ago

Thanks for the suggestion, I'll look into it. :)

Jared Davidson Over a year ago

Worked perfectly! Thanks!

Moritz Lang Over a year ago

Great! I'm glad it helped. :)

JDM · Accepted Answer · 2017-01-18 20:59:19Z

1

The problem is you're in a closure, that doesn't expect a return type.. How are you call this function?

Some ideas: * Pass a closure to this function, which then gets called, instead of trying to return.

Keep a mapping of the results somewhere, update that from the closure and always check against that mapping.

Also, it looks like instead of

if snapshot.value != nil {
        userBool = true
        return userBool
    }
    else {
        userBool = false
        return userBool
    }

You could just do this:

guard snapshot = snapshot else { return }
return snapshot.value

answered Jan 18, 2017 at 20:59

JDM

8931 gold badge9 silver badges20 bronze badges

1 Comment

Jared Davidson Over a year ago

Thanks for your suggestions! Keeping a mapping of the results doesn't seem like the best solution for myself as the function should only be called once. I'll look into passing a closure, thanks for that idea. :)

Artem Stepanenko · Accepted Answer · 2017-01-18 21:16:31Z

1

The only way to make it return what you want is possible if the observeSingleEvent(...) function executes the closure synchronously to its call.

If it's true, you can try the following:

func checkIfUserExists(userID : String) -> Bool {
    var userBool = false
    var usersRef = FIRDatabase.database().reference()
    usersRef.child("users").child(userID).observeSingleEvent(of: .value, with: {
        userBool = $0.value != nil
    })
    return userBool
}

If the closure of observeSingleEvent(...) is called after a while, return a result of your method in a closure as Moritz suggested, not as a return value.

answered Jan 18, 2017 at 21:16

Artem Stepanenko

3,5326 gold badges31 silver badges51 bronze badges

3 Comments

vadian Over a year ago

Unfortunately it's not true, observeSingleEvent works asynchronously, so the function will always return false.

Artem Stepanenko Over a year ago

Then there's no other option. Instead of returning a Bool there should be a completion closure as other guys suggested.

Jared Davidson Over a year ago

Thanks for your suggestion, and yep, as stated it's asynchronous, but I got it working by adding a closure. Thanks for the input! :)

Carolina · Accepted Answer · 2017-01-18 21:19:12Z

0

Another way is to create a delegate protocol and call it inside the closure

answered Jan 18, 2017 at 21:19

Carolina

4574 silver badges19 bronze badges

Collectives™ on Stack Overflow

Return value for function in nested function (Swift 3 | Xcode)

4 Answers 4

3 Comments

1 Comment

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

3 Comments

1 Comment

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related