> The meaning of the proposed while is not at all a pair for where, since where > clauses in while loops would do the same thing as while clauses in for loops. > That's crazy.
It sounds crazy, but it’s the nature of the while loop. A where clause in a while loop also has a different result than a where clause in a for loop. > filter() is and prefix(while:) will be available on all sequences. The > for...in loop only traverses through sequences. > > The meaning of the proposed while is not at all a pair for where, since where > clauses in while loops would do the same thing as while clauses in for loops. > That's crazy. > > On Tue, Jun 7, 2016 at 06:20 Vladimir.S via > swift-evolution<swift-evolution@swift.org(mailto:swift-evolution@swift.org)>wrote: > > My +1 to the proposal and for Charlie's opinion. I believe `while` in `for` > > loop would be very handy and helpful in some situations, it is a pair for > > existed `where`, its meaning is obvious, and its existence can't depend on > > existence of any method in collections. I'd like to see a formal proposal > > for this feature. > > > > On 07.06.2016 8:18, Charlie Monroe via swift-evolution wrote: > > >I strongly disagree. > > > > > >Exchanging > > > > > >for result in results where result.value != .Warning while result.value != > > >.Error { > > >/// ... > > >} > > > > > >for either > > > > > >for result in results.filter({ $0.value != .Warning }).prefix(while: { > > >$0.value != .Error })) { > > >/// ... > > >} > > > > > >or > > > > > >for result in results { > > >if result.value == .Warning { continue } > > >if result.value == .Error { break } > > > > > >/// ... > > >} > > > > > >Seems like an absolute step back. Not to mention filter(_:) doesn't return > > >a lazy collection, but will recreate it, while the `where` will do > > >on-the-fly check. > > > > > >>On Jun 7, 2016, at 1:34 AM, Xiaodi Wu via swift-evolution > > >><swift-evolution@swift.org(mailto:swift-evolution@swift.org)<mailto:swift-evolution@swift.org>>wrote: > > >> > > >>Personally, given this discussion and the one about `where` in if and > > >>while statements, I would not be opposed to elimination of `where` in > > >>control statements altogether. > > >> > > >>My reasoning would be that words like filter and prefix unambiguously > > >>indicate what happens to elements of a sequence for which the predicate > > >>returns false, whereas words like where and while are ambiguous. > > >> > > >>On Mon, Jun 6, 2016 at 17:52 Tim > > >>Vermeulen<tvermeu...@me.com(mailto:tvermeu...@me.com) > > >><mailto:tvermeu...@me.com>>wrote: > > >> > > >>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) > > >><mailto:tvermeu...@me.com>(mailto: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>(mailto:swift-evolution@swift.org > > >><mailto: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>(mailto:tseit...@icloud.com > > >><mailto: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>(mailto:swift-evolution@swift.org > > >><mailto: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 > > >><mailto:swift-evolution@swift.org>)(mailto: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 > > >><mailto:swift-evolution@swift.org>)(mailto: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>(mailto: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>(mailto: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(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) > > https://lists.swift.org/mailman/listinfo/swift-evolution > > > _______________________________________________ swift-evolution mailing list swift-evolution@swift.org https://lists.swift.org/mailman/listinfo/swift-evolution
