Unexpected Non-Void Return Value in Void Function Swift3

Swift - unexpected non-void return value in void function

You are missing return type in your method header.

func calculateDistance(location: CLLocation) -> CLLocationDistance {

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Seemingly my answer looks as an inferior duplicate, so some addition.

Functions (including methods, in this case) declared without return types are called as void function, because:

func f() {
    //...
}

is equivalent to:

func f() -> Void {
    //...
}

Usually, you cannot return any value from such void functions.
But, in Swift, you can return only one value (I'm not sure it can be called as "value"), "void value" represented by ().

func f() {
    //...
    return () //<- No error here.
}

Now, you can understand the meaning of the error message:

unexpected non-void return value in void function

You need to change the return value or else change the return type Void to some other type.

Unexpected non-void return value in void function Swift3

The problem is that you are trying to return a non-void value from inside a closure, which only returns from the closure, but since that closure expects a void return value, you receive the error.

You cannot return from an asynchronous function using the standard return ... syntax, you have to declare your function to accept a completion handler and return the value from the async network call inside the completion handler.

func findChat(string: String, completion: @escaping (Chat?)->()) {
    var returnValue: (Chat?)
    let url = getChatsURL
    let Parameters = [ "title" : string ]

    Alamofire.request("\(url)", method: .post, parameters: Parameters).validate().responseString { response in
        if let anyResponse = response.result.value {
            self.responseFromServer = anyResponse
        }
        if self.responseFromServer == "" {
            completion(nil)
        } else {
            let ref = DatabaseReference.chats.reference()
            let query = ref.queryOrdered(byChild: "uid").queryEqual(toValue: (self.responseFromServer))
                query.observe(.childAdded, with: { snapshot in
                completion(Chat(dictionary: snapshot.value as! [String : Any]))
            })
        }
    }
}

Then you can call this function and use the return value like this:

findChat(string: "inputString", completion: { chat in
    if let chat = chat {
        //use the return value
    } else {
        //handle nil response
    }
})

Unexpected non-void return value in void function (Swift 3)

If you are calling an async method like Alamofire.request, then you need notify when this async method is over with closures

Try with this

func postUser(username: String, pass: String, finishedClosured:@escaping ((Bool)->Void))  {
            Alamofire.request("https://someAPI.com/auth/login", method: .post, parameters: ["email": contact, "password": pass], encoding: URLEncoding.default, headers: ["Accept":"application/json"]).responseJSON { (response) in

                switch(response.result) {
                    case .success(let value):
                        let json = JSON(value)
                        print("JSON: \(json)")
                        print(json["data"]["result"])
                        finishedClosured(true)
                    case .failure(let error):
                        print(error)
                        finishedClosured(false)
                }
            }
        }

Use it

 self.postUser(username: "your UserName", pass: "Your Pass") { (result) in
            if(result){
                debugPrint("All is fine")
            }else{
                debugPrint("All is wrong")
            }
        }

Why i am getting Unexpected non-void return value in void function error while returning value in swift?

I think AuthManager.shared.saveAddressAsWorkHome(params) { (response) in this is asynchronous closure and you are try to return a value in it so you getting this error.

You can not return from asynchronous function directly. You have to add a completion handler on your method and return the value from async in completion handler

So you have to change your function

func getLatDestination(completion : @escaping (Double) -> ()){
var params = [String: Any]()
params[ParametersKeys.access_token] = KeyChain.getAccessToken()!
params[ParametersKeys.address] = googlePlaceObject?.results.first?.formattedAddress
params[ParametersKeys.latitude] = googlePlaceObject?.results.first?.geometry.location.lat
params[ParametersKeys.longitude] = googlePlaceObject?.results.first?.geometry.location.lng
params[ParametersKeys.googlePlaceId] = googlePlaceObject?.results.last?.placeId
params[ParametersKeys.login_type] = 1
    
AuthManager.shared.saveAddressAsWorkHome(params) { (response) in
    if response.flag == RESPONSE_FLAGS.flag_143 {
        if let addressData = response.response["addresses"] as? [[String: Any]] {
                    completion(addressData[0]["lat"])

        }
    }
}

And when you call your function

getLatDestination(completion: {ret in
        print(ret) 
    })

Unexpected non-void return value in void function - Swift 4 (Firebase, Firestore)

Since the firebase operation gives you a callback closure, and the calls made asynchronously, I believe it wont be possible for you to directly return from closures. However, you can return an escaping closure indicating true or false as follows...

func checkUserWith(email: String, completion: @escaping (Bool) -> Void)
{
    let usersDB = database.collection("users")
    usersDB.whereField("email", isEqualTo: email).getDocuments { (snapshot, error) in

        if error != nil
        {
            print("Error: \(error?.localizedDescription ?? "")")
            completion(false)
        }

        for document in (snapshot?.documents)! {
            if document.data()["email"]! as! String == email {
                completion(true)
                return
            }
        }

        completion(false)
    }
}

Then when you call this method:

checkUserWith(email: emailHere) { (isSucceeded) in
    if isSucceeded {
        //it exists, do something
    } else {
        //user does not exist, do something else
    }
}

Unexpected non-void return value in void function when returns an array

You can´t just return words in your closure. First of all it´s an async method second you need to return a value outside of the closure which will be called before the closure. You need to have a completionHandler instead of returning Array<Any>. In that case you can pass the value if and when it succeeds. Something like this:

func getWords(onCompletion: @escaping (Array<Any>) -> Void) {
    ref = Database.database().reference()
    ref.child("addedWords").observe(.value, with: { (DataSnapshot) in
        var tempWords = DataSnapshot.value as! [String:AnyObject]
        var words = Array(tempWords.keys)
        print(words)
        onCompletion(words)
    })
}

To call it:

getWords(onCompletion: { (words) in
    print(words)
})

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