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How to find the index of the first matching array element

Swift version: 5.1

Paul Hudson    @twostraws   

If you have an array of items and want to find the first item that matches a specific condition, you should use the index(where:) method. This accepts a closure of code to use as a test, applies that test to all elements in an array, then returns the index of the first item to match it. If no item matches you’ll get back nil, so be prepared to unwrap the optional you get sent back.

For example, if we had an array of numbers:

let numbers = [2, 4, 6, 8, 9, 10]

We could find the first odd number like this:

let firstOdd = numbers.index { $0 % 2 == 1 }

That will send back 4 as an optional integer, because the first odd number (9) is at index four.

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