What is the ternary operator?

Swift version: 5.10

Paul Hudson @twostraws May 28th 2019

The ternary operator allows you to run a check and return one of two values depending on the result of that check – it has the name “ternary” because it works with three values rather than two or one like other operators. You’ll often see it written as ?: but in practice the ? and : are used separately.

Like I said, the ternary operator is used with three values: the check to run, what to return if the check is true, and what to return if the check is false. For example, if we had a score constant that contained an integer, we could make a result constant equal either to “Pass” or “Fail” depending on the value of score:

let score = 88
let result = score > 85 ? "Pass" : "Fail"

You can read that ternary as “if score is greater than 85 return Pass otherwise return Fail.” Because score was set to 88, result will be set to Pass.

The ternary operator usually makes your code harder to read and understand, so it doesn’t get much use.