[swift-evolution] [Proposal] Add Array binary search to the standard library

Guillaume DIDIER guillaume.didier.2014 at polytechnique.org
Wed Sep 7 05:08:28 CDT 2016

Basically for a binary search to work it needs to operate on a sorted array (it is a necessary invariant).

It is really interesting when you make a lot of search in the same sorted array, hence I would +1 the sorted array, with initializer from an array.

Guillaume  DIDIER
M. +33 (0)7 70 43 18 40
guillaume.didier at polytechnique.edu <mailto:guillaume.didier at polytechnique.edu?subject=>
www.polytechnique.edu <http://www.polytechnique.edu/>

> Le 7 sept. 2016 à 12:04, Haravikk via swift-evolution <swift-evolution at swift.org> a écrit :
>> On 7 Sep 2016, at 10:08, Charlie Monroe via swift-evolution <swift-evolution at swift.org> wrote:
>> Aside from this being additive (i.e. out of scope for Swift 4), this requires the array to be sorted in order for the search to work - who will guarantee this? The caller? What happens when this is called on an array that is not sorted? You likely get nil, while the item is in the array (false negative).
>> This would probably make sense by not extending Array itself, but introducing SortedArray which would automatically keep its members sorted instead - this way there would be a guarantee that the array is sorted and the user won't have to deal with sorting the array. It would however be at the cost of O(log N) for insertion…
> I don't think this is really a problem, just needs to be clear that behaviour is undefined if the array wasn't previously sorted (or not in the same order).
> On this topic there was a previous proposal that was undergoing refinements after being initially rejected, you can find it here:
> https://github.com/apple/swift-evolution/blob/master/proposals/0074-binary-search.md
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