I agree. `where` and `while` fit so well in for loops, IMO, because a for loop already loops over the elements - this is exactly what filter and prefix also do. You’ve even given the current element a name (for myElement in …) and it’s more natural to just use that name in a `where` clause or `whil`e clause, than to have to deal with $0 inside a closure.
> I strongly disagree. > > Exchanging > > forresultinresultswhereresult.value != .Warningwhileresult.value != .Error { > /// ... > } > > > for either > > forresultinresults.filter({ $0.value != .Warning }).prefix(while: { $0.value > != .Error })) { > /// ... > } > > > or > > forresultinresults { > ifresult.value == .Warning {continue} > ifresult.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)>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)>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)>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)>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)>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)>: > > > >>>>>> > > > >>>>>>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)>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) > > > >>>>>>>>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) > > > >>>>>>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) > > > >>>>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