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Check whether all items in an array match a condition

Written by Paul Hudson    @twostraws

Swift doesn’t have a built-in way of checking whether all items in an array match a condition, but it doesn’t take much work to create one. In fact, we can write an extension on Collection so the functionality becomes available on other types of collection, such as sets.

Here’s the code:

extension Collection {
    func all(_ predicate: (Element) throws -> Bool) rethrows -> Bool {
        for item in self {
            let result = try predicate(item)

            if !result {
                return false
            }
        }

        return true
    }
}

With that code, you can now check whether all items in an array of numbers are under 10:

[1, 2, 3, 4, 5].all { $0 < 10 }

Available from iOS 8.0

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