on Fri Jul 22 2016, Matthew Johnson <matthew-AT-anandabits.com> wrote:
>> On Jul 22, 2016, at 9:04 PM, Dave Abrahams via swift-evolution >> <swift-evolution@swift.org> wrote: >> >> >> on Fri Jul 22 2016, Matthew Johnson <swift-evolution@swift.org >> <mailto:swift-evolution@swift.org>> wrote: >> > >>>> On Jul 22, 2016, at 8:37 PM, Xiaodi Wu via swift-evolution >>>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: >>>> >>>> On Fri, Jul 22, 2016 at 8:20 PM, Dave Abrahams via swift-evolution >>>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>> >>>> <mailto:swift-evolution@swift.org <mailto:swift-evolution@swift.org>>> >>>> wrote: >>>> >>>> on Fri Jul 22 2016, Daniel Duan <daniel-AT-duan.org >>>> <http://daniel-at-duan.org/>> wrote: >>>> >>>>>> On Jul 22, 2016, at 3:00 PM, Dave Abrahams via swift-evolution >>>>>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>>>>> <mailto:swift-evolution@swift.org <mailto:swift-evolution@swift.org>>> >>>>>> wrote: >>>>>> >>>>>> >>>>>> on Fri Jul 22 2016, Daniel Duan >>>>>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>>>>> <mailto:swift-evolution@swift.org <mailto: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: >>>>>> >>>>> >>>>>>>> On Jul 22, 2016, at 11:05 AM, Dave Abrahams 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 <mailto:swift-evolution@swift.org> >>>>>>>> <mailto: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>> >>>>>>>> <mailto:swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>>>>>>> <mailto:swift-evolution@swift.org <mailto:swift-evolution@swift.org>>> >>>>>>>> <mailto:swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>>>>>>> <mailto:swift-evolution@swift.org <mailto: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: >>>>>>>> >>>>>>>>> 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)”. >>> >>> The point of this design is that `===` means identity and that `.same ` >>> also means identity. >>> >>> Since this is new territory I suppose we get to decide what identity >>> means for floating point. Should +0 and -0 have the same identity or >>> not? I’ll leave the answer to folks more knowledgable about numerics >>> than I. >> >> It's settled law >> https://en.wikipedia.org/wiki/IEEE_floating_point#Total-ordering_predicate >> <https://en.wikipedia.org/wiki/IEEE_floating_point#Total-ordering_predicate> >> :-) > > Yes, assuming we want to define identity in terms of the IEEE definition of > total ordering. We do :-) >> >>> >>> >>>> >>>> /// - 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 >>>>>>>>>> <mailto:swift-evolution@swift.org >>>>>>>>>> <mailto:swift-evolution@swift.org>>> >>>>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>> >>>>>>>>>>> On Jul 21, 2016, at 6:19 PM, Xiaodi Wu >>>>>>>>>>> <xiaodi...@gmail.com <mailto:xiaodi...@gmail.com> >>>>>>>>>>> <mailto:xiaodi...@gmail.com <mailto: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 <mailto:swift-evolution@swift.org> >>>>>>>>>>>> <mailto:swift-evolution@swift.org >>>>>>>>>>>> <mailto: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 <mailto: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> >>>>>>>>>> <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> >>>>>>>>> <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>> >>>>>>>>> >>>>>>>> >>>>>>>> -- >>>>>>>> Dave >>>>>>>> >>>>>>>> _______________________________________________ >>>>>>>> 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 <mailto:swift-evolution@swift.org> >>>>>>>> <mailto:swift-evolution@swift.org <mailto: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 >>>>>>>> <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 >>>>>>>> <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 >>>>>>>> <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 >>>>>>>> <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> >>>>>>> <mailto:swift-evolution@swift.org <mailto: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 >>>>>>> <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 >>>>>>> <https://lists.swift.org/mailman/listinfo/swift-evolution> >>>>>>> <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> >>>>>> <mailto:swift-evolution@swift.org <mailto: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 >>>>>> <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 >>>>>> <https://lists.swift.org/mailman/listinfo/swift-evolution> >>>>>> <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> >>>> <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> >>>> <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
