I can't argue with that. I guess I was really only opposed to using the half-open range for Double and other theoretically non-discrete types, for the reasons I listed. I have no objections to clamping with a half-open Integer range; I just hadn't considered further restricting the Bound of the Range in use. arr[idx.clamped(to: arr.indices)] looks amazing.
> On Mar 11, 2017, at 12:29 AM, Jaden Geller <[email protected]> wrote: > >> >> On Mar 10, 2017, at 8:04 PM, Robert Bennett via swift-evolution >> <[email protected]> wrote: >> >> I really like this proposal, and think that it does have a place in Swift 4. >> Two quick notes in light of the discussion: first, I think it should be >> called clamped, not clamp; second, I think it should only take ClosedRange. >> More on those later, but first I'll respond to the six questions raised by >> Xiaodi. >> >>> 1. Is it truly a frequent operation? >> I think so. I've certainly wished for it on an occasion or two. I settle for >> min(upper, max(lower, value)). >> >>> 2. Is the helper more readable? Is the composed equivalent obvious at a >>> glance? >> Definitely (or I imagine it will be once we get the details figured out). >> There are two equivalent forms of the min-max version, the other being >> max(lower, min(upper, value)), not to mention the commutativity of the >> arguments themselves. I am under the impression that Swift is not a big fan >> of having multiple equivalent ways to do the same thing — that was part of >> the reason ++ was nixed. value.clamp(to: closedRange) is clear and is not >> interchangeable with any one thing in the language. >> >>> 3. Does the helper have the flexibility to cover all common cases? >> I see three cases: value < lower, lower <= value <= upper, and upper < >> value. All are covered. >> >>> 4. Is there a correctness trap with the composed equivalent? Is there a >>> correctness trap with the helper? >> I don't think so, if we limit to ClosedRange. >> >>> 5. Is there a performance trap with the composed equivalent? Or with the >>> helper? >> I don't know, is there a significant cost associated to constructing a >> ClosedRange solely for the purpose of using its bounds? I would imagine not, >> but someone who knows more about Swift can answer. >> >>> 6. Does the helper actually encourage misuse? >> I don't see how, if we limit its argument to ClosedRange. >> >> >> Going back to my earlier points — I think that to keep things in line with >> Swift's naming conventions, this function should be called clamped, as it >> returns a modified version of the calling object. Alternatively, we could >> follow the standard set by other numeric types and provide the non-mutating >> clamped and the mutating clamp, like multiplied/multiply for Double. >> >> Finally, I don't think it makes mathematical sense to clamp to a non-closed >> range. Refer back to the original definition proposed, `min(upperBound, >> max(lowerBound, value))`. ClosedRange was proposed as a convenience for >> providing those bounds. This makes sense because a ClosedRange contains its >> bounds. Since (mathematical) non-closed ranges don't contain their bounds, >> it doesn't make sense to use a non-closed range to provide those bounds. > > I think open ranges should be supported, but not for all `Comparable` types. > It would however be reasonable to support it for types with discrete ordered > values, all `Integer` types for example. I think we might be able to provide > it for `T: Strideable where T.Stride: Integer` even. We definitely cannot > provide it for all types though; it’s nonsensical to clamp a real value to a > closed range. > >> >> Also, the above notwithstanding, I have a hard time figuring out when you >> would actually want to constrain a number to be strictly less than an upper >> bound, violating Question 1 above. If this behavior were really desired, >> better to be explicit and subtract the appropriate delta — 1 for Int, >> Double.epsilon (or whatever it's called) for Double. I definitely foresee a >> correctness trap with the non-closed Range. >> >> Another reason not to allow half-open ranges is because of their asymmetry. >> Half open ranges are only open at their upper end, so you would have the >> ability to open-clamp from above but not from below. Seems arbitrary (see >> Question 3). > > We already have this asymmetry. Adding a clamp function doesn’t worsen it. > Besides, we have half-open [above] ranges because they are useful for indices: > > `arr[idx.clamped(to: arr.startIndex..<arr.endIndex)` > > We can even write this! > > `arr[idx.clamped(to: arr.indices)]` > > This seems like a useful enough feature to consider it IMO. > >> >> _______________________________________________ >> swift-evolution mailing list >> [email protected] <mailto:[email protected]> >> https://lists.swift.org/mailman/listinfo/swift-evolution >> <https://lists.swift.org/mailman/listinfo/swift-evolution>
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