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How to use one-sided ranges

Swift version: 5.1

Paul Hudson    @twostraws   

One-sided ranges allow us to skip either the start or end of a range to have Swift infer the starting point for us. As an example, consider this array:

let characters = ["Dr Horrible", "Captain Hammer", "Penny", "Bad Horse", "Moist"]

If we wanted to read only the first three items from that array, we could use characters[..<3] – we skipped the start point, so Swift will automatically infer the start of the array:

let bigParts = characters[..<3]

That will create an array containing ["Dr Horrible", "Captain Hammer", "Penny"].

Similarly, we could skip the end of the range to have Swift infer the end of the array, like this:

let smallParts = characters[3...]

That will create an array containing ["Bad Horse", "Moist"].

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Available from iOS 8.0

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