Extending Array to check if it is sorted in Swift?

Question

I want to extend Array class so that it can know whether it is sorted (ascending) or not. I want to add a computed property called isSorted. How can I state the

Answer 1

In Swift 2.0 you can now extend protocols!

extension CollectionType where Generator.Element: Comparable {

    public var isSorted: Bool {

        var previousIndex = startIndex
        var currentIndex = startIndex.successor()

        while currentIndex != endIndex {

            if self[previousIndex] > self[currentIndex] {
                return false
            }

            previousIndex = currentIndex
            currentIndex = currentIndex.successor()
        }

        return true
    }

}

[1, 2, 3, 4].isSorted // true
["a", "b", "c", "e"].isSorted // true
["b", "a", "c", "e"].isSorted // false
[/* Anything not implementing `Comparable` */].isSorted // <~~ Type-error

Note that because we're using Indexable.Index instead of a simple Int as an index we have to use a while-loop instead, which looks a bit less pretty and clear.