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

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

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.

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.

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

> 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.

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.

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