'NSLog' is unavailable: Variadic function is unavailable in swift

Question

I'm new to swift. when I'm learning just basics I got this error at NSLog

Here is my code :

import UIKit

class ViewController: UIViewController {
    
     var myString: NSString?

    override func viewDidLoad() {
        super.viewDidLoad()
        myString = "himanth"
        print(myString)
        NSLog("%@" , myString)
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

If I am declaring myString like this

var myString: NSString!

It's fine to use NSLog and I can able to see console as well.

But declaring string like this causing problem

var myString: NSString?

It reflects at NSLog and showing error.

What is the problem with that?

Rashwan L · Accepted Answer · 2019-11-26T21:04:15.320

26

If you declare var myString: NSString? as an optional then you need to make sure it has a value before you pass it to the NSLog.

So you could do it like this then NSLog("%@" , myString!). If myString is nil and you put ! the program will crash and you will get

fatal error: unexpectedly found nil while unwrapping an Optional value.

But if it has a value the program will continue as normal and print out

2016-10-03 10:26:25.077 Swift3.0[65214:1579363] Test

I wrote myString = "Test".

Another example as @Grimxn mentioned is the coalescing operator.

NSLog("%@", myString ?? "<nil>")

edited Nov 26 '19 at 21:04

answered Oct 03 '16 at 08:27

Rashwan L

38,237
7
103
107

3

Better to use `NSLog("%@", myString ?? "")` surely? – Grimxn Oct 03 '16 at 13:48
That´s absolutely an alternative @Grimxn – Rashwan L Oct 03 '16 at 13:51

pkamb · Answer 2 · 2018-09-13T18:30:47.197

19

NSLog() cannot print Swift Optionals.

let optional: String?
NSLog("%@", optional) // 'NSLog' is unavailable: Variadic function is unavailable

let nonOptional: String
NSLog("%@", nonOptional) // Ok!

NSLog("%@", optional ?? "value-if-nil") // Ok!

Fix by passing a non-optional value to NSLog() instead.

NOTE:

print() can print Swift Optionals.

edited Sep 13 '18 at 18:30

answered Jan 15 '17 at 22:20

pkamb

33,281
23
160
191

score 3 · Answer 3 · edited Feb 13 '19 at 12:59

3

Have the same problem, accepted answer doesn't help.

func handleSomeResp(_ response: DataResponse<Any>) {
    NSLog("handle error: %@", response)
}

as you see, there is nothing about optionals. I guess it because of <Any>, and any type, unclear for NSLog, watch similar problem here: . Edit this answer if you have a solution to parse generics for NSLog.

edited Feb 13 '19 at 12:59

Eric Aya

69,473
35
181
253

answered Feb 13 '19 at 12:14

Zaporozhchenko Oleksandr

4,660
3
26
48

score 0 · Answer 4 · answered Sep 28 '21 at 15:10

NSLog does not support any types except String. You cannot pass, i.e. your custom struct / enum instance as NSLog variadic argument.

Instead use description variable to show up necessary details about your instance. Your class / struct / enum could conform CustomStringConvertible to unify the way to access description variable as well.

'NSLog' is unavailable: Variadic function is unavailable in swift

4 Answers4