How can I test if an integerForKey is equal to nil? Using NSUserDefaults

Question

So far, I have a function that tries to see if someone already has a code, and if they do not already have one, then it would generate one for them. func checkID() -> Int{

    if (NSUserDefaults.standardUserDefaults().integerForKey("Code") != nil) {

    }
    else{
        var code = Int(arc4random_uniform(1000000000))
        NSUserDefaults.standardUserDefaults().setInteger(code, forKey: "Code")
    }
    return NSUserDefaults.standardUserDefaults().integerForKey("Code")
}

I get an error message when I try to to say NSUserDefaults.standardUserDefaults().integerForKey("Code") != nil

The error message I get is "Type 'Int' does not conform to protocol 'NilLiteralConvertible'"

What can I do to try to get around this? What am I doing wrong?

Answer 1

The integerForKey always returns a value. If nothing's there, just 0.

So you should check like that:

if let currentValue = NSUserDefaults.standardUserDefaults().objectForKey("Code"){
    //Exists
}else{
    //Doesn't exist
}

Answer 2

The short answer is "you can't." There's no way to tell if a zero result for integerForKey represents a stored zero value, or no value.

Christian's answer of using objectForKey (which returns and optional) and optional binding is the correct answer.

Edit:

It would be quite easy to add an extension to UserDefaults with a function that returned an Optional Int:

extension UserDefaults {
    func int(forKey key: String) -> Int? {
        return object(forKey: key) as? Int
    }
}

(I suspect that if Apple were designing the Foundations framework today, using Swift, integer(forKey:) would return an Optional(Int).)

Answer 3

You should be able to remove the '!= nil'. For instance,

if (NSUserDefaults.standardUserDefaults().integerForKey("Code")) {

}
else{
    var code = Int(arc4random_uniform(1000000000))
    NSUserDefaults.standardUserDefaults().setInteger(code, forKey: "Code")
}
return NSUserDefaults.standardUserDefaults().integerForKey("Code")

Simply retrieving the value of the key should return false if the integer is not found.