How to remove the first or last item from an array

Swift version: 5.10

Paul Hudson @twostraws May 28th 2019

Arrays have built-in methods for removing the first or last items, but there’s a subtle difference between them.

First, there are two ways of removing the last item: popLast() and removeLast(). Both remove the last item from the array, but popLast() returns an optional – if the array was empty, you get back nil. If you call removeLast() on an empty array, your app crashes.

So, in this example last1 will contain 5 and last2 will contain 4:

var numbers = [1, 2, 3, 4, 5]
let last1 = numbers.popLast()
let last2 = numbers.removeLast()

As for removing items from the start of the array, there’s only one method: removeFirst(). This, like removeLast(), will crash your app if called when the array is empty.

So, continuing the above example, this will put 1 into first1:

let first1 = numbers.removeFirst()

There is no popFirst() because it’s an expensive operation and the developers want you to think twice – each time you remove an item from the front the rest of the items have to move down, so trying to use popFirst() in a loop would be inefficient.