Swift last(:where) element in an array

Question

For an array:

var arr = [3,2,1,2,1,4,5,8,6,7,4,2]

I can find the first matching element

arr.first(where: {$0 == 2})!

But the last

arr.last(where: {$0 == 2})

Returns:

cannot call value of non-function type 'Int?'

Why?

What version of Swift (or Xcode) are you using? `last(where:)` was added in Swift 4.2 (Xcode 10). — rmaddy, Sep 03 '18 at 00:32
Related: https://stackoverflow.com/questions/50279988/in-swift-array-is-there-a-function-that-returns-the-last-index-based-in-where-c — Martin R, Sep 03 '18 at 03:32

score 2 · Accepted Answer · answered Sep 03 '18 at 00:34

2

last(where:) was added in Swift 4.2 (Xcode 10).

If you need to find the last match using Swift 4.1 or earlier, you can do:

let last = arr.reversed().first { $0 == 2 }

answered Sep 03 '18 at 00:34

rmaddy

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And for those worried about the performance of this: worry not, `reversed()` simply makes a wrapper around the source array, and just does some index math (`count - 1 - i`) to access an index `i`. There's no array copying going on. – Alexander Sep 03 '18 at 01:06
@Alexander TIL! Cool. – Oscar Apeland Sep 03 '18 at 12:19

Leo Dabus · Answer 2 · 2018-09-03T12:17:29.943

1

As already mentioned by rmaddy this method still in beta. If you would like to add this functionality also to Swift 4.1 you can extend BidirectionalCollection as follow:

extension BidirectionalCollection {
    func last(where predicate: (Element) throws -> Bool) rethrows -> Element? {
        return try reversed().first(where: predicate)
    }
}

edited Sep 03 '18 at 12:17

answered Sep 03 '18 at 01:06

Leo Dabus

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Swift last(:where) element in an array

2 Answers2