I didn’t mean we should really get rid of the `where` clause, it’s great. I guess the point I was trying to make is that we can use a `where` clause with a `for` loop in Swift, despite the existence of the `filter` method. So despite `prefix(while:)` in Swift 3, there might be room for a `while` clause. I think it makes the code a lot more readable, much like how `where` can make a `for` loop a lot more readable than using `filter`.
> The burden of proof for adding new features is different from that for taking > away existing features. > > If a feature doesn't yet exist, a successful proposal will show how it > provides additional and non-trivial utility. If a feature already exists, a > successful proposal to remove it will show how it is harmful to the language > or contrary to the direction in which it is evolving. > > On Mon, Jun 6, 2016 at 15:38 Tim > Vermeulen<tvermeu...@me.com(mailto:tvermeu...@me.com)>wrote: > > The functionality of the `where` clause in `for` loops also already can be > > mimicked using `filter`. Wouldn’t we have to get ride of the `where` clause > > by that logic? > > > > >The functionality being asked for here is already accepted for inclusion > > >to Swift as a method on Sequence named `prefix(while:)` (SE-0045): > > > > > >`for element in array.prefix(while: { someCondition($0) }) { ... }` > > >On Mon, Jun 6, 2016 at 14:31 T.J. Usiyan via > > >swift-evolution<swift-evolution@swift.org(mailto:swift-evolution@swift.org)(mailto:swift-evolution@swift.org)>wrote: > > >>(As I said, I can live with `while`. I am simply presenting a potential > > >>point of confusion.) > > >>You aren't evaluating the statements in the loop 'while' the condition > > >>isn't met. The first time that the condition isn't met, evaluation of the > > >>loop stops. I get that this is technically true for the `while` construct > > >>but I suggest that the only reason that it works there is that 'stopping > > >>the first time that the condition isn't met' *is* the construct. Here, we > > >>have a loop that we execute for each thing and we're tacking > > >>on/intermingling the `while` construct. > > >> > > >> > > >> > > >>On Mon, Jun 6, 2016 at 2:19 PM, Thorsten > > >>Seitz<tseit...@icloud.com(mailto:tseit...@icloud.com)(mailto:tseit...@icloud.com)>wrote: > > >>> > > >>>>Am 06.06.2016 um 19:43 schrieb Tim Vermeulen via > > >>>>swift-evolution<swift-evolution@swift.org(mailto:swift-evolution@swift.org)(mailto:swift-evolution@swift.org)>: > > >>>> > > >>>>I also considered `until`, but it would be a bit confusing that `where` > > >>>>makes sure a condition is met, while `until` makes sure the condition > > >>>>isn’t met. I think `while` makes more sense because it corresponds to > > >>>>`break` in the same way that `where` corresponds to `continue`. > > >>> > > >>>That's a good argument! The only drawback is that `while` and `where` > > >>>look quite similar at a glance. > > >>> > > >>>-Thorsten > > >>> > > >>>> > > >>>>>`while`, to me, actually reads like it should do what `where` does. > > >>>> > > >>>>To me, `while` reads like it should stop the loop once the condition > > >>>>isn’t met, just like in a while loop. > > >>>> > > >>>>>I hadn't thought about `while` in this regard but wouldn't `until` > > >>>>>make more sense? `while`, to me, actually reads like it should do what > > >>>>>`where` does. In any case, whether it is `while` or `where`, this > > >>>>>seems like a reasonable feature in my opinion. > > >>>>> > > >>>>>TJ > > >>>>> > > >>>>>On Mon, Jun 6, 2016 at 5:15 AM, Tim Vermeulen via > > >>>>>swift-evolution<swift-evolution@swift.org(mailto:swift-evolution@swift.org)(mailto:swift-evolution@swift.org)(mailto:swift-evolution@swift.org)>wrote: > > >>>>>>We can already use a where clause in a for loop like this: > > >>>>>> > > >>>>>>for element in array where someCondition(element) { > > >>>>>>// … > > >>>>>>} > > >>>>>> > > >>>>>>which basically acts like > > >>>>>> > > >>>>>>for element in array { > > >>>>>>guard someCondition(element) else { continue } > > >>>>>>// … > > >>>>>>} > > >>>>>> > > >>>>>>Sometimes you want to break out of the loop when the condition isn’t > > >>>>>>met instead. I propose a while clause: > > >>>>>> > > >>>>>>for element in array while someCondition(element) { > > >>>>>>// … > > >>>>>>} > > >>>>>> > > >>>>>>which would be syntactic sugar for > > >>>>>> > > >>>>>>for element in array { > > >>>>>>guard someCondition(element) else { break } > > >>>>>>… > > >>>>>>} > > >>>>>> > > >>>>>>I can see this particularly being useful if we have a sorted array > > >>>>>>and we already know that once the condition isn’t met, it won’t be > > >>>>>>met either for subsequent elements. Another use case could be an > > >>>>>>infinite sequence that we want to cut off somewhere (which is simply > > >>>>>>not possible using a where clause). > > >>>>>>_______________________________________________ > > >>>>>>swift-evolution mailing list > > >>>>>>swift-evolution@swift.org(mailto:swift-evolution@swift.org)(mailto:swift-evolution@swift.org)(mailto:swift-evolution@swift.org) > > >>>>>>https://lists.swift.org/mailman/listinfo/swift-evolution > > >>>>_______________________________________________ > > >>>>swift-evolution mailing list > > >>>>swift-evolution@swift.org(mailto:swift-evolution@swift.org)(mailto:swift-evolution@swift.org) > > >>>>https://lists.swift.org/mailman/listinfo/swift-evolution > > >> > > >>_______________________________________________ > > >>swift-evolution mailing list > > >>swift-evolution@swift.org(mailto:swift-evolution@swift.org)(mailto:swift-evolution@swift.org) > > >>https://lists.swift.org/mailman/listinfo/swift-evolution > > > > > > > > >_______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution > > > _______________________________________________ swift-evolution mailing list swift-evolution@swift.org https://lists.swift.org/mailman/listinfo/swift-evolution
