filter(extractingWhere:) On Wed, Jun 22, 2016 at 18:53 Dave Abrahams via swift-evolution < [email protected]> wrote:
> > on Wed Jun 22 2016, Xiaodi Wu <[email protected]> wrote: > > > I'll duly oblige with some pushback on `suchThat`. I get that you're > trying > > to clarify whether filter retains or gets rid of elements that match the > > predicate, but I don't think "filter such that" expresses this idea at > all. > > > > Comparing to "filter where," "filter such that" is equally susceptible to > > misinterpretation that you are filtering to remove elements that are > > matched. For example: "find me some apples, filtering such that are > > bruised." > > Hahaha, that's a very different interpretation of “such” that I hadn't > considered! OK, suppose it was “soEach:” ? > > let primes = xs.filter(soEach: isPrime) > > > I'd suggest that if you want to be perfectly clear, you'd need something > > like `filter(keepingWhere:)`. > > let primes = xs.filter(keepingWhere: isPrime) > > A slight problem is that filter is nonmutating, so all elements are > “kept.” But maybe that's just Dave being overly concerned with unlikely > misinterpretations at the cost of “naturalness.” > > Further thoughts? > > > On Wed, Jun 22, 2016 at 18:33 Dave Abrahams via swift-evolution < > > [email protected]> wrote: > > > >> > >> on Tue Jun 21 2016, Dave Abrahams <[email protected]> wrote: > >> > >> > on Mon Jun 20 2016, Brent Royal-Gordon <[email protected]> > >> wrote: > >> > > >> >>> A couple of weeks ago we started to notice that we had some > >> poorly-named > >> >>> closure parameters and argument labels in the standard library, so > we > >> >>> did a complete audit of the standard library's APIs and came up > with a > >> >>> preliminary proposal for changes, which we applied in a branch and > you > >> >>> can review in https://github.com/apple/swift/pull/2981. Let's > please > >> >>> carry on further discussion here rather than in the pull request, > >> though. > >> >> > >> >> In general, I like this; `orderingBy` is a particularly nice > >> >> improvement over the old `isOrderedBefore` convention. > >> > > >> > I don't really love the use of “by”, FWIW, but I thought > `orderingWith` > >> > was more confusable (ordering A with B might swap A and B, whereas the > >> > parameter is a closure). It could be argued, though, that I am being > >> > overly concerned with unlikely misinterpretations, at the cost of > >> > “naturalness”—a known weakness of mine ;-). Anyway, as ever I'm open > to > >> > discussion on this. > >> > > >> >> A few specific comments about things I don't like: > >> >> > >> >> * In `map` and `flatMap`, I'm not sure how much `transform` buys us > >> >> over `elementTransform`. > >> > > >> > I think you mean the converse. And I agree that `elementTransform` > >> > is probably not an improvement over `transform`. > >> > >> ...and I've gone back to `transform` in my PR. > >> > >> >> * In general, I'm not a fan of most of the changes away from `where` > >> >> labels. > >> > > >> > The only such changes I can find are in > >> > > >> > https://github.com/apple/swift/pull/2981/commits/3418eede88d724ad23731fe8f412f51e03cf5106 > >> > > >> > Note that part of this change was to make all filter closures > >> > consistent; in the main `filter` API there was no label at all. > >> > However, we felt that there's a real clarity problem with the polarity > >> > of the argument (we talk about “filtering things out” but the closure > >> > indicates which elements to keep). And we couldn't find a > “where”-based > >> > name that began to clarify it. > >> > > >> > I will argue that even changing to “suchThat,” as in the PR, does not > >> > sufficiently clarify the closure's polarity, and the only true fix for > >> > filter is to use a different base name (some have suggested “select,” > >> > and I have other ideas), but that is out of scope for this particular > >> > set of changes. So if the community is happier with a “where” label > >> > here I can live with it. I do think “suchThat” is marginally clearer. > >> > >> I have not received any further pushback on “suchThat,” so I've left it > >> alone. > >> > >> > > >> >> Those are a nice, straightforward convention applied broadly across > >> >> the Sequence APIs. (Yes, I criticized `where` as a method name in > >> >> another thread, but I don't think `where` is a problem when there's a > >> >> function base name to give it context.) When they don't work, that's > >> >> usually because of a less-than-ideal base name. I'm not saying that > >> >> *all* base names that aren't compatible with `where` should be > >> >> changed, but rather that if `where` is not enough, that's an API > >> >> smell. > >> >> > >> >> * In particular, `elementWhere` is not a good label for the same > >> >> reason that `removeElement` is not a good name. Session 403 last week > >> >> actually talked about this between roughly minutes 8 and 11. (I'm > sure > >> >> you know about its content; you probably saw it before we did.) > >> > > >> > Yes I do, and I think you misinterpreted the message in that session. > >> > There's nothing wrong with repeating type information when it's > >> > necessary for clarity or fluency at the use-site. In the case of > >> > `contains(elementWhere:)`, it's there for fluency: > >> > > >> > customers.contains(where: isSingle) > >> > > >> > doesn't read as well as: > >> > > >> > customers.contains(elementWhere: isSingle) > >> > > >> > The point is not to imagine that every argument should be preceded by > >> > a noun, and repetition of type information is often the result of > >> > trying to do that. > >> > > >> >> * I like `separatedWhere` on `split`, but I think the Equatable > >> >> version needs a similar renaming. > >> > > >> > That's a nice thought; I think it's arguably out-of-scope here, > though. > >> > > >> >> Perhaps `separatedBy`? `separatedOn`? The usual opposite of `where`, > >> >> `of`, doesn't work here. (Alternatively, `separatedWhere` could be > >> >> `separatorWhere` instead, but that's not quite as elegant.) > >> > > >> > I'd want to consider variations of `separatingAt` or `onSeparator` or > >> > `atSeparator` too... which makes me thing “separatedWhere” might not > be > >> > as good as “separatingWhere” for the closure version. > >> > > >> >> * I'm very uncomfortable with the amount of weight > >> >> `accumulatingResultBy` adds to `reduce`. `combinedBy` seems perfectly > >> >> cromulent to me. I'm even more concerned by your suggestion in the > >> >> pull request body of > >> >> `accumulating(startingFrom:combiningBy:)`. `reduce` is a subtle and > >> >> slightly confusing operation; adding more words to its call sites > will > >> >> not solve that problem. If you want to invent a new name from whole > >> >> cloth, I would probably use something like `combining(with > >> >> initialResult: T, by nextResult: (T, Element) -> T)`. (For that > >> >> matter, while we're working in this area, `sequence(first:next:)` > >> >> could use a similar coat of paint.) > >> > > >> > As with `filter(suchThat:`, `reduce(accumulatingResultBy:` is > attempting > >> > to solve with an argument label what IMO is a grave weakness in > clarity > >> > of the base name. If you read the documentation for `reduce`, you'll > >> > see that it's all about accumulating a result, and if you consider > that > >> > its current signature often leads to O(N^2) behavior and we are > thinking > >> > about adding an overload that takes its “accumulator” inout, the > >> > arguments for avoiding the name “accumulate” get progressively weaker. > >> > But as noted earlier, changing base names is out-of-scope for this > >> > proposal. As with “filter,” I could live with leaving this alone, > >> > though I do believe “accumulatingResultBy:” is a real improvement in > >> > clarity. > >> > >> ...but I think it's overly specific at the expense of smoothness. So > >> I've removed `Result` from that name. > >> > >> >> * I agree with the comment on GitHub that `invoke` should be > >> >> `execute`. > >> > > >> > Why? Rationales help. > >> > > >> >> If you see a distinction between the two cases on the number of > >> >> arguments, I would then suggest `passTo` as the label on these > >> >> methods: `views.forEach(passTo: addSubview)`, > >> >> `withUnsafeBufferPointer(&bytes, passTo: Data.init(buffer:))`. > >> > > >> > Those are intriguing ideas, but that direction tends to suggest this > >> > would be better: > >> > > >> > views.passEach(to: addSubview) > >> > passUnsafeBufferPointer(to: Data.init(buffer:)) > >> > > >> > ...until you pass a trailing closure: > >> > > >> > views.passEach { addSubView($0) } > >> > passUnsafeBufferPointer { Data.init(buffer:$0) } > >> > > >> > (note: withUnsafeBufferPointer takes only one argument, a closure). > >> > > >> >> > >> >> * It's a little odd that you're using `comparingBy` for `Equatable` > >> >> and `orderingBy` for `Comparable`. Did you judge `equatingBy` to be > >> >> too awkward? > >> > > >> > Yes, and because it's not “equating,” which would mean using equality > >> > (==) it's “testing equivalence” with respect to the predicate. > >> > > >> >> Perhaps the real problem is that `Equatable` ought to be `Comparable` > >> >> and `Comparable` ought to be `Orderable`? > >> > > >> > I don't think so, personally, but regardless I consider such a change > >> > out-of-scope for this proposal. > >> > > >> >> Or maybe `comparingBy` should just be something more general, like > >> >> `matchingBy`? That would make perfectly sensible but slightly odd use > >> >> cases like this one read better: > >> >> > >> >> let isAnIdiot = luggageCombination.starts(with: [1, 2, 3, 4, > >> >> 5], matchingBy: <=) // Matches [1,2,3,4,5], but also [1,1,1,1,1], > >> >> [1,2,3,2,1], etc. > >> > > >> > That would not be legal, as <= is not an equivalence relation. You > >> > could think about redefining the meaning of `starts(with:` to not > >> > require an equivalence relation, but that's something I'm not > confident > >> > *I* know how to do meaningfully, and regardless is again out-of-scope. > >> > > >> >> Very soon (hopefully), I will be posting an early draft of a proposal > >> >> renaming the various first/last/prefix/suffix/etc. APIs. I believe > the > >> >> only place it touches on your proposal is in > >> >> `starts(with:isEquivalent:)`, but I think your changes to the second > >> >> parameter label can be easily incorporated into what I'm doing. > >> > > >> > Great! > >> > >> I'm going to write up the proposal ASAP based on the current PR unless I > >> get more feedback. > >> > >> Thanks, > >> > >> -- > >> Dave > >> > >> _______________________________________________ > >> swift-evolution mailing list > >> [email protected] > >> https://lists.swift.org/mailman/listinfo/swift-evolution > >> > > _______________________________________________ > > swift-evolution mailing list > > [email protected] > > https://lists.swift.org/mailman/listinfo/swift-evolution > > > > -- > Dave > > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution >
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