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<[email protected](mailto:[email protected])>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<[email protected](mailto:[email protected])>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<[email protected](mailto:[email protected])(mailto:[email protected])>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<[email protected](mailto:[email protected])(mailto:[email protected])(mailto:[email protected])>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<[email protected](mailto:[email protected])(mailto:[email protected])(mailto:[email protected])>wrote:
> > > >>>>>
> > > >>>>>>Am 06.06.2016 um 19:43 schrieb Tim Vermeulen via
> > > >>>>>>swift-evolution<[email protected](mailto:[email protected])(mailto:[email protected])(mailto:[email protected])>:
> > > >>>>>>
> > > >>>>>>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<[email protected](mailto:[email protected])(mailto:[email protected])(mailto:[email protected])(mailto:[email protected])>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).
> > > >>>>>>>>_______________________________________________
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> > > >>>>>>>>https://lists.swift.org/mailman/listinfo/swift-evolution
> > > >>>>>>_______________________________________________
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> > > >>>>
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