How do you use the Optional variable in a ternary conditional operator?

Question

I want to use an Optional variable with the ternary conditional operator but it is throwing error this error: optional cannot be used as boolean. What am I doing wrong?

var str1: String?
var myBool:Bool
myBool = str1 ? true : false

score 85 · Accepted Answer · edited Sep 28 '16 at 20:59

85

You can not assign string value to bool but You can check it str1 is nil or not like this way :

myBool = str1 != nil ? true : false
print(myBool)

It will print false because str1 is empty.

edited Sep 28 '16 at 20:59

alessionossa

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answered Nov 12 '14 at 08:04

Dharmesh Kheni

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10

You don't need the conditional expression, just do: `myBool = str1 != nil` – TimK Feb 29 '16 at 18:39

Abhijeet · Answer 2 · 2015-09-18T10:17:09.807

Nil Coalescing Operator can be used as well. The code below uses the ternary conditional operator and forced unwrapping (a!) to access the value wrapped inside a when a is not nil, and to return b otherwise

Normal Ternary Operator :

output = a != nil ? a! : b Apple Developer Link : Please refer to Demo Link

In Swift 1.2 & 2, above line of code is replaced by a shorter format:

output = a ?? b

Demo Link : The nil coalescing operator (a ?? b) unwraps an optional a if it contains a value, or returns a default value b if a is nil.

score 5 · Answer 3 · answered Dec 08 '16 at 13:14

5

This even works well if the value you want is a property or result of a function call on an optional (in Swift 3.0):

return peripheral?.connected ?? false

answered Dec 08 '16 at 13:14

Robert Atkins

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that's not answering the same question, because you assume we want the value - if it exists, and nil otherwise. While we want two different expressions - based on an arbitrary conditionals. something like a>3 ? (4+7) : (6/4) in C. – Motti Shneor Jul 30 '17 at 13:33

score 5 · Answer 4 · answered Feb 17 '18 at 12:34

5

Ternary operators operate on three targets. Like C, Swift has only one ternary operator, the ternary conditional operator (a ? b : c).

Example usage on tableView -

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
     return section == 2 ?  4 :  1
}

indicates if section equal to 2 then it return 4 otherwise 1 on false.

answered Feb 17 '18 at 12:34

Jack

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This answer doesn't address OP's specific requirement for Optionals though – Skwiggs Aug 12 '20 at 10:31

Skwiggs · Answer 5 · 2020-08-12T10:39:46.297

To add on the already very good answers, sometimes you need the convenience of the ternary operator but also need to perform changes on the wrapped value, such as;

var fullName = lastName != nil ? "\(firsName) \(lasName!)" : firstName

But you don't want to force unwrap (even though this situation would be fine).

Then you can actually use Optional.map:

var fullName = lastName.map({ "\(firstName) \($0)" }) ?? firstName

The completion block passed to .map is only called if the wrapped value ($0) is not nil. Otherwise, that function just returns nil, which you can then easily coalesce with the ?? operator.

score 0 · Answer 6 · answered Oct 17 '17 at 08:06

In case the comparison is based on some condition

 let sliderValue = Float(self.preferenceData.getLocationRadius().characters.count > 1 ?self.preferenceData.getLocationRadius():"0.1")

Here the function getLocationRadius() returns a String. One more thing if we don't put a space between 1 and ? it results in an syntax error

How do you use the Optional variable in a ternary conditional operator?

6 Answers6

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