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

Answer 1

change function return type String to Bool

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

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

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

        return false
    }
}