On Fri, Jul 22, 2016 at 9:09 PM, Dave Abrahams via swift-evolution < swift-evolution@swift.org> wrote:
> > on Fri Jul 22 2016, Xiaodi Wu <swift-evolution@swift.org> wrote: > > > On Fri, Jul 22, 2016 at 8:45 PM, Dave Abrahams <dabrah...@apple.com> > wrote: > > > >> > >> on Fri Jul 22 2016, Xiaodi Wu <xiaodi.wu-AT-gmail.com> wrote: > >> > >> > On Fri, Jul 22, 2016 at 8:20 PM, Dave Abrahams via swift-evolution < > >> > swift-evolution@swift.org> wrote: > >> > > >> >> > >> >> on Fri Jul 22 2016, Daniel Duan <daniel-AT-duan.org> wrote: > >> >> > >> >> >> On Jul 22, 2016, at 3:00 PM, Dave Abrahams via swift-evolution < > >> >> swift-evolution@swift.org> wrote: > >> >> >> > >> >> >> > >> >> >> on Fri Jul 22 2016, Daniel Duan <swift-evolution@swift.org > <mailto: > >> >> swift-evolution@swift.org>> wrote: > >> >> >> > >> >> > > >> >> >>>> On Jul 22, 2016, at 11:05 AM, Dave Abrahams via swift-evolution > >> >> >>>> <swift-evolution@swift.org > >> >> >>>> <mailto:swift-evolution@swift.org>> > >> wrote: > >> >> >>>> > >> >> >>>> > >> >> >>>> on Thu Jul 21 2016, Duan > >> >> >>> > >> >> >>>> <swift-evolution@swift.org > >> >> >>>> <mailto:swift-evolution@swift.org> > >> >> >>>> <mailto:swift-evolution@swift.org <mailto: > >> swift-evolution@swift.org > >> >> >>> > >> >> >>>> wrote: > >> >> >>>> > >> >> >>>>> Great proposal. I want to second that areSame may mislead user > to > >> >> >>>>> think this is about identity. > >> >> >>>>> > >> >> >>>>> I like areEquivalent() but there may be better names. > >> >> >>>> > >> >> >>>> It really *is* about identity as I posted in a previous message. > >> But > >> >> >>>> that doesn't change the fact that areEquivalent might be a > better > >> >> name. > >> >> >>>> It's one of the things we considered; it just seemed long for no > >> real > >> >> >>>> benefit. > >> >> >>>> > >> >> >>> > >> >> >>> If the addresses of the arguments aren’t being used, then we > don’t > >> >> consider > >> >> >>> them part of their *identity*. I can follow this logic. My fear > is > >> >> most users > >> >> >>> won’t make this leap on their own and get the same initial > >> impression > >> >> as I did. > >> >> >>> It's entirely possible this fear is unfounded. Some educated > >> >> bikesheding > >> >> >>> wouldn't hurt here IMO :) > >> >> >> > >> >> >> Well, it's still a very real question whether we ought to have the > >> >> >> additional API surface implied by areSame, or wether we should > >> collapse > >> >> >> it with ===. > >> >> >> > >> >> > > >> >> > To spell this out (because I had to think about it for a second): > === > >> >> will be derived from > >> >> > <=>, > >> >> > but also becomes default implementation for ==, which remains open > for > >> >> > customization. > >> >> > >> >> I was imagining roughly this (untested): > >> >> > >> >> /// Two references are identical if they refer to the same > >> >> /// instance. > >> >> /// > >> >> /// - Note: Classes with a more-refined notion of “identical” > >> >> /// should conform to `Identifiable` and implement `===`. > >> >> func ===(lhs: AnyObject, rhs: AnyObject) -> Bool { > >> >> ObjectIdentifier(lhs) == ObjectIdentifier(rhs) > >> >> } > >> >> > >> >> /// Supports testing that two values of `Self` are identical > >> >> /// > >> >> /// If `a` and `b` are of type `Self`, `a === b` means that > >> >> /// `a` and `b` are interchangeable in most code. A conforming > >> >> /// type can document that specific observable characteristics > >> >> /// (such as the `capacity` of an `Array`) are inessential and > >> >> /// thus not to be considered as part of the interchangeability > >> >> /// guarantee. > >> >> /// > >> >> /// - Requires: `===` induces an equivalence relation over > >> >> /// instances. > >> >> /// - Note: conforming types will gain an `==` operator that > >> >> /// forwards to `===`. > >> >> /// - Note: Types that require domain-specific `==` > >> >> /// implementations with different semantics (e.g. floating > >> >> /// point) should define a more-specific overload of `==`, > >> >> /// which will be used in contexts where the static type is > >> >> /// known to the compiler. > >> >> /// - Note: Generic code should usually use `==` to compare > >> >> /// conforming instances; that will always dispatch to `===` > >> >> /// and will be unaffected by more specific overloads of > >> >> /// `==`. > >> >> protocol Identifiable { // née Equatable name is negotiable > >> >> func ===(_: Self, _: aSelf) -> Bool > >> >> } > >> >> > >> >> /// Default definition of `==` for Identifiable types. > >> >> func ==<T: Identifiable>(lhs: T, rhs: T) -> Bool { > >> >> return lhs === rhs > >> >> } > >> >> > >> >> /// Conforming types have a default total ordering. > >> >> /// > >> >> /// If `a` and `b` are of type `Self`, `a <=> b` means that > >> >> /// `a` and `b` are interchangeable in most code. A conforming > >> >> /// type can document that specific observable characteristics > >> >> /// (such as the `capacity` of an `Array`) are inessential and > >> >> /// thus not to be considered as part of the interchangeability > >> >> /// guarantee. > >> >> /// > >> >> /// - Requires: `<=>` induces a total ordering over > >> >> /// instances. > >> >> /// - Requires: the semantics of `<=>` are consistent with > >> >> /// those of `===`. That is, `(a <=> b) == .equivalent` > >> >> /// iff `a === b`. > >> >> > >> > > >> > For floating point, I'd hope that `a === b` if `(a <=> b) == .same` > *but > >> > not iff*. This is to satisfy IEEE 754: "Comparisons shall ignore the > sign > >> > of zero (so +0 = −0)". > >> > >> By “comparisons” they mean the traditional comparison operators, not all > >> possible comparisons you might want to do. > >> > > > > I don't believe so, but I could be corrected by Steve. > > They can't legislate the comparisons that you can possibly make. For > example, code is allowed to compare bit representations. That > comparison would of course distinguish '+0' from '-0', since floats have > to store a sign bit! Sorry, that's not what I meant--actually, I'm not terribly sure what I meant to say there. Please ignore. > > They list 26 comparison relations and don't go into what they call `=` > > until later, so I take than as an example. > > > >> > >> That single equal sign in their text corresponds to == in the world > >> being proposed, so that's fine. > >> > >> > > >> > > >> >> /// - Note: conforming types will gain `<`, `<=`, `>`, and `>=` > >> >> /// operators defined in terms of `<=>`. > >> >> /// - Note: Types that require domain-specific `<`, etc. > >> >> /// implementations with different semantics (e.g. floating > >> >> /// point) should define more-specific overloads of those > >> >> /// operators, which will be used in contexts where the > >> >> /// static type is known to the compiler. > >> >> /// - Note: Generic code can freely use `<=>` or the traditional > >> >> /// comparison operators to compare conforming instances; > >> >> /// the result will always be supplied by `<=>` > >> >> /// and will be unaffected by more specific overloads of > >> >> /// the other operators. > >> >> protocol Comparable : Identifiable { > >> >> func <=> (lhs: Self, rhs: Self) -> Ordering > >> >> } > >> >> > >> >> /// Default implementations of `<`, `<=`, `>`, and `>=`. > >> >> extension Comparable { > >> >> static func <(lhs: Self, rhs: Self) -> Bool { > >> >> return (lhs <=> rhs) == .ascending > >> >> } > >> >> static func <=(lhs: Self, rhs: Self) -> Bool { > >> >> return (rhs <=> lhs) != .ascending > >> >> } > >> >> static func >(lhs: Self, rhs: Self) -> Bool { > >> >> return (lhs <=> rhs) == .descending > >> >> } > >> >> static func >=(lhs: Self, rhs: Self) -> Bool { > >> >> return (rhs <=> lhs) != .descending > >> >> } > >> >> } > >> >> > >> >> > I like this idea. If we keep === as a separate thing, now users > have 3 > >> >> “opportunities” to define > >> >> > equality. The must be few, if any, use cases for this. > >> >> > > >> >> > Would love to see if anyone on the list can give us an example. > >> >> Otherwise we should make > >> >> > areSame === again™! > >> >> > > >> >> >>> > >> >> >>>>> Daniel Duan > >> >> >>>>> Sent from my iPhone > >> >> >>>>> > >> >> >>>>>> On Jul 21, 2016, at 6:32 PM, Robert Widmann via > swift-evolution > >> >> >>>>>> <swift-evolution@swift.org> wrote: > >> >> >>>>>> > >> >> >>>>>> > >> >> >>>>>>> On Jul 21, 2016, at 6:19 PM, Xiaodi Wu <xiaodi...@gmail.com> > >> >> wrote: > >> >> >>>>>>> > >> >> >>>>>>> This is nice. Is `areSame()` being proposed because static > `==` > >> is > >> >> >>>>>>> the status quo and you're trying to make the point that `==` > in > >> the > >> >> >>>>>>> future need not guarantee the same semantics? > >> >> >>>>>> > >> >> >>>>>> Yep! Equivalence and equality are strictly very different > >> things. > >> >> >>>>>> > >> >> >>>>>>> > >> >> >>>>>>> Nit: I think the more common term in stdlib would be > >> >> >>>>>>> `areEquivalent()`. Do you think `same` in that context > >> (independent > >> >> >>>>>>> of the word "ordering") might erroneously suggest identity? > >> >> >>>>>> > >> >> >>>>>> There is room for improvement here. Keep ‘em coming. > >> >> >>>>>> > >> >> >>>>>>> > >> >> >>>>>>> > >> >> >>>>>>>> On Thu, Jul 21, 2016 at 8:11 PM, Robert Widmann via > >> >> >>>>>>>> swift-evolution > >> >> >>>>>>>> <swift-evolution@swift.org> wrote: > >> >> >>>>>>>> Hello Swift Community, > >> >> >>>>>>>> > >> >> >>>>>>>> Harlan Haskins, Jaden Geller, and I have been working on a > >> >> >>>>>>>> proposal to clean up the semantics of ordering relations in > the > >> >> >>>>>>>> standard library. We have a draft that you can get as a > gist. > >> >> >>>>>>>> Any feedback you might have about this proposal helps - > though > >> >> >>>>>>>> please keeps your comments on Swift-Evolution and not on the > >> gist. > >> >> >>>>>>>> > >> >> >>>>>>>> Cheers, > >> >> >>>>>>>> > >> >> >>>>>>>> ~Robert Widmann > >> >> >>>>>>>> > >> >> >>>>>>>> > >> >> >>>>>>>> > >> >> >>>>>>>> > >> >> >>>>>>>> > >> >> >>>>>>>> _______________________________________________ > >> >> >>>>>>>> swift-evolution mailing list > >> >> >>>>>>>> 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 > >> >> >>>>> _______________________________________________ > >> >> >>>>> swift-evolution mailing list > >> >> >>>>> swift-evolution@swift.org > >> >> >>>>> https://lists.swift.org/mailman/listinfo/swift-evolution > >> >> >>>>> > >> >> >>>> > >> >> >>>> -- > >> >> >>>> Dave > >> >> >>>> > >> >> >>>> _______________________________________________ > >> >> >>>> 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 > >> >> >>>> <https://lists.swift.org/mailman/listinfo/swift-evolution> > >> >> >>>> <https://lists.swift.org/mailman/listinfo/swift-evolution > >> >> >>>> <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 > >> >> >>> <https://lists.swift.org/mailman/listinfo/swift-evolution> > >> >> >>> > >> >> >> > >> >> >> -- > >> >> >> Dave > >> >> >> > >> >> >> _______________________________________________ > >> >> >> swift-evolution mailing list > >> >> >> swift-evolution@swift.org > >> >> >> <mailto:swift-evolution@swift.org> > >> >> >> https://lists.swift.org/mailman/listinfo/swift-evolution > >> >> >> <https://lists.swift.org/mailman/listinfo/swift-evolution> > >> >> > >> >> -- > >> >> Dave > >> >> _______________________________________________ > >> >> swift-evolution mailing list > >> >> swift-evolution@swift.org > >> >> https://lists.swift.org/mailman/listinfo/swift-evolution > >> >> > >> > >> -- > >> Dave > >> > > _______________________________________________ > > swift-evolution mailing list > > swift-evolution@swift.org > > https://lists.swift.org/mailman/listinfo/swift-evolution > > > > -- > Dave > > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution >
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