How to loop over non-nil items in an array

Swift version: 5.0

Paul Hudson    @twostraws    March 28th 2019

Consider an array of items containing some optionals, like this one:

let numbers: [Int?] = [1, nil, 3, nil, 5]

If you want to loop over all the items and print them out, you’d write something like this:

for number in numbers {
    print(number)
}

However, that prints out all items in their current state: optionally wrapped integers for some, nil for others.

With a small change to that loop, you can have Swift unwrap all the optionals then only enter the loop for any that contain a value – any nil items are ignored. This is done using for case let syntax, like this:

for case let number? in numbers {
    print(number)
}

That will print the numbers 1, 3, and 5.

Available from iOS – learn more in my book Pro Swift

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