<div dir="ltr">On Fri, Jul 22, 2016 at 9:53 PM, Dave Abrahams <span dir="ltr"><<a href="mailto:dabrahams@apple.com" target="_blank">dabrahams@apple.com</a>></span> wrote:<br><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class=""><br>
on Fri Jul 22 2016, Xiaodi Wu <<a href="http://xiaodi.wu-AT-gmail.com" rel="noreferrer" target="_blank">xiaodi.wu-AT-gmail.com</a>> wrote:<br>
<br>
</span><span class="">> On Fri, Jul 22, 2016 at 9:38 PM, <<a href="mailto:jaden.geller@gmail.com">jaden.geller@gmail.com</a>> wrote:<br>
><br>
>> This seems reasonable to me. I don't see why `===` has to do a total order<br>
>> comparison when we already have another operator, `<=>`, that does that.<br>
>><br>
><br>
> I take it back. It wouldn't solve the issue that generic `<` would<br>
> still behave in surprising ways, where two equal floating point values<br>
> represented differently might be less than each other or greater than<br>
> each other.<br>
<br>
</span>I wonder if that's really a problem. What generic algorithm are you<br>
going to run on a collection of floats where it *would* be problematic?<br></blockquote><div><br></div><div>I don't think they exist currently in stdlib, but any algorithm where you're taking a subsequence prefix from a sorted collection up to a given value might return a chunk of values that equal the value but compare less-than ("ascending").</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hmm, stableSort would not necessarily preserve the order of zeros in the<br>
original collection if it contained both positive and negative zeros.<br>
<span class=""><br>
> I think what we really want is all identity and comparison divorced<br>
> from IEEE totalOrder.<br>
<br>
</span>That might work. Thanks for thinking this problem through; keep it up!<br>
<div class="HOEnZb"><div class="h5"><br>
>> On Jul 22, 2016, at 7:35 PM, Xiaodi Wu <<a href="mailto:xiaodi.wu@gmail.com">xiaodi.wu@gmail.com</a>> wrote:<br>
>><br>
>> On Fri, Jul 22, 2016 at 9:28 PM, Dave Abrahams <<a href="mailto:dabrahams@apple.com">dabrahams@apple.com</a>><br>
>> wrote:<br>
>><br>
>>><br>
>>> on Fri Jul 22 2016, Xiaodi Wu <<a href="http://xiaodi.wu-AT-gmail.com" rel="noreferrer" target="_blank">xiaodi.wu-AT-gmail.com</a>> wrote:<br>
>>><br>
>>> > On Fri, Jul 22, 2016 at 9:13 PM, Matthew Johnson <<br>
>>> <a href="mailto:matthew@anandabits.com">matthew@anandabits.com</a>><br>
>>> > wrote:<br>
>>> ><br>
>>> >><br>
>>> >> On Jul 22, 2016, at 9:10 PM, Xiaodi Wu <<a href="mailto:xiaodi.wu@gmail.com">xiaodi.wu@gmail.com</a>> wrote:<br>
>>> >><br>
>>> >> On Fri, Jul 22, 2016 at 9:08 PM, Matthew Johnson <<br>
>>> <a href="mailto:matthew@anandabits.com">matthew@anandabits.com</a>><br>
>>> >> wrote:<br>
>>> >><br>
>>> >>><br>
>>> >>> On Jul 22, 2016, at 9:04 PM, Xiaodi Wu <<a href="mailto:xiaodi.wu@gmail.com">xiaodi.wu@gmail.com</a>> wrote:<br>
>>> >>><br>
>>> >>> On Fri, Jul 22, 2016 at 8:57 PM, Matthew Johnson <<br>
>>> <a href="mailto:matthew@anandabits.com">matthew@anandabits.com</a>><br>
>>> >>> wrote:<br>
>>> >>><br>
>>> >>>><br>
>>> >>>> On Jul 22, 2016, at 8:54 PM, Xiaodi Wu via swift-evolution <<br>
>>> >>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br>
>>> >>>><br>
>>> >>>> On Fri, Jul 22, 2016 at 8:52 PM, Jaden Geller via swift-evolution <<br>
>>> >>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br>
>>> >>>><br>
>>> >>>>> "The totalOrder predicate will order these cases, and it also<br>
>>> >>>>> distinguishes between different representations of NaNs and between<br>
>>> the<br>
>>> >>>>> same decimal floating point number encoded in different ways."<br>
>>> >>>>> - [Wikipedia](<br>
>>> >>>>><br>
>>> <a href="https://en.wikipedia.org/wiki/IEEE_floating_point#Total-ordering_predicate" rel="noreferrer" target="_blank">https://en.wikipedia.org/wiki/IEEE_floating_point#Total-ordering_predicate</a><br>
>>> >>>>> )<br>
>>> >>>>><br>
>>> >>>>> Sounds like `===` should not return `true` for zeros of different<br>
>>> >>>>> signs, then.<br>
>>> >>>>><br>
>>> >>>><br>
>>> >>>> Fair enough; the result of that will be, as Pyry noted above, that:<br>
>>> >>>><br>
>>> >>>> ```<br>
>>> >>>> [-0.0, 1.0, .nan, 0.0].firstIndex(of: 0.0) //=> 3, not 0<br>
>>> >>>> ```<br>
>>> >>>><br>
>>> >>>><br>
>>> >>>> Maybe we need floating point specific implementations of some<br>
>>> algorithms<br>
>>> >>>> to resolve this problem?<br>
>>> >>>><br>
>>> >>>> It doesn’t seem like there is a way to provide the semantics<br>
>>> required by<br>
>>> >>>> generic algorithms and still provide the expected behavior for<br>
>>> floating<br>
>>> >>>> point values.<br>
>>> >>>><br>
>>> >>><br>
>>> >>> Well, what I'm trying to say is that generic algorithms such as<br>
>>> >>> `index(of:)` require only an equivalence relation. For floating point<br>
>>> >>> types, there are three ways to slice it:<br>
>>> >>><br>
>>> >>> 1. NaN != NaN and +0 == -0 [what the traditional comparison operators<br>
>>> are<br>
>>> >>> constrained to do]<br>
>>> >>> 2. NaN == NaN, +0 == -0, and the same number encoded different ways<br>
>>> >>> compare equal<br>
>>> >>> 3. NaN == NaN, +0 != -0, and the same number encoded different ways<br>
>>> >>> compare not equal<br>
>>> >>><br>
>>> >>> Both #2 and #3 can fall out of valid equivalence relations; if `===`<br>
>>> >>> behaved like #2 for FloatingPoint types, then generic algorithms work<br>
>>> just<br>
>>> >>> fine. If we insist on using a total ordering defined by `<=>` all the<br>
>>> time,<br>
>>> >>> then we've got problems.<br>
>>> >>><br>
>>> >>><br>
>>> >>> And if we don’t then we’re back to 3 different concepts of equality.<br>
>>> >>> There is definitely a tradeoff no matter what we choose.<br>
>>> >>><br>
>>> >><br>
>>> >> If some types have three concepts of equality, each with their<br>
>>> particular<br>
>>> >> use, why must we eliminate one of them?<br>
>>> >><br>
>>> >><br>
>>> >> This isn’t about eliminating concepts of equality for a type. They can<br>
>>> >> have 42 if they want.<br>
>>> >><br>
>>> >> This is about the right way to define the semantics of specific<br>
>>> >> protocols. It says nothing about additional notions of equality a<br>
>>> type may<br>
>>> >> have available.<br>
>>> >><br>
>>> >> The difficulty is finding a design for the protocols that makes sense<br>
>>> with<br>
>>> >> floating point types because we want them to be able to conform to the<br>
>>> >> protocols.<br>
>>> >><br>
>>> ><br>
>>> > Agreed. My argument is that if a Comparable can define its own `===`,<br>
>>> still<br>
>>> > supplying a valid equivalence relation but not being constrained by a<br>
>>> > contract that `(a <=> b) == .same` iff `a === b`, then we are good to go<br>
>>> > with floating point types.<br>
>>><br>
>>> How would that work? Can you spell out the implications, show how <=><br>
>>> and === would be implemented, and describe what it would mean for<br>
>>> algorithms?<br>
>>><br>
>><br>
>> Right. I'm not married to this solution anymore, but I do think it could<br>
>> work. There would still be a relationship required between `===` and `<=>`.<br>
>> Namely:<br>
>><br>
>> `a === b` if `(a <=> b) == .same`<br>
>><br>
>> But for some values a and b, it is permitted that `a === b && (a <=> b) !=<br>
>> .same`. That is, two identical values may be ordered in a total ordering<br>
>> based on *inessential* qualities.<br>
>> Generic algorithms that need to produce a stable ordering of elements will<br>
>> use `<=>`. Those such as `index(of:)` will use `===` to test for identity.<br>
>> Wouldn't that work?<br>
>><br>
>> ><br>
>>> > On Jul 22, 2016, at 6:48 PM, Dave Abrahams via swift-evolution <<br>
>>> >>>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> on Fri Jul 22 2016, Jaden Geller <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br>
>>> >>>>><br>
>>> >>>>> For floating point, I'd hope that `a === b` if `(a <=> b) == .same`<br>
>>> >>>>> *but not iff*. This is to satisfy IEEE 754: "Comparisons shall<br>
>>> >>>>> ignore the sign of zero (so +0 = −0)".<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> I don't see why both `(+0) === (-0)` and `(+0) <=> (-0)` can't<br>
>>> return<br>
>>> >>>>> `true` and `.same`, respectively. This doesn't break the total<br>
>>> >>>>> ordering of values. `===` doesn't do raw memory comparison. They're<br>
>>> >>>>> "identical", so it ought to return `true`.<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> It ought to do whatever IEEE-754 specifies that its total ordering<br>
>>> test<br>
>>> >>>>> does. That is, IEEE-754 gets to decide whether the difference<br>
>>> between<br>
>>> >>>>> +0 and -0 is “essential” to IEEE-754 floating point types, or not.<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> On Jul 22, 2016, at 6:37 PM, Xiaodi Wu via swift-evolution<br>
>>> >>>>> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br>
>>> >>>>><br>
>>> >>>>> On Fri, Jul 22, 2016 at 8:20 PM, Dave Abrahams via swift-evolution<br>
>>> >>>>> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>>><br>
>>> >>>>> wrote:<br>
>>> >>>>><br>
>>> >>>>> on Fri Jul 22 2016, Daniel Duan <daniel-AT-duan.org<br>
>>> <<a href="http://daniel-at-duan.org" rel="noreferrer" target="_blank">http://daniel-at-duan.org</a>><br>
>>> >>>>> <<a href="http://daniel-at-duan.org/" rel="noreferrer" target="_blank">http://daniel-at-duan.org/</a>>> wrote:<br>
>>> >>>>><br>
>>> >>>>> On Jul 22, 2016, at 3:00 PM, Dave Abrahams via swift-evolution<br>
>>> >>>>> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>>><br>
>>> >>>>> wrote:<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> on Fri Jul 22 2016, Daniel Duan<br>
>>> >>>>> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>>>><br>
>>> >>>>> wrote:<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> On Jul 22, 2016, at 11:05 AM, Dave Abrahams via swift-evolution<br>
>>> >>>>> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>>>><br>
>>> >>>>> wrote:<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> on Thu Jul 21 2016, Duan<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>>>>><br>
>>> >>>>> wrote:<br>
>>> >>>>><br>
>>> >>>>> Great proposal. I want to second that areSame may mislead user to<br>
>>> >>>>> think this is about identity.<br>
>>> >>>>><br>
>>> >>>>> I like areEquivalent() but there may be better names.<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> It really *is* about identity as I posted in a previous message.<br>
>>> But<br>
>>> >>>>> that doesn't change the fact that areEquivalent might be a better<br>
>>> name.<br>
>>> >>>>> It's one of the things we considered; it just seemed long for no<br>
>>> real<br>
>>> >>>>> benefit.<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> If the addresses of the arguments aren’t being used, then we don’t<br>
>>> >>>>> consider<br>
>>> >>>>> them part of their *identity*. I can follow this logic. My fear is<br>
>>> most<br>
>>> >>>>> users<br>
>>> >>>>> won’t make this leap on their own and get the same initial<br>
>>> impression<br>
>>> >>>>> as I did.<br>
>>> >>>>> It's entirely possible this fear is unfounded. Some educated<br>
>>> bikesheding<br>
>>> >>>>> wouldn't hurt here IMO :)<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> Well, it's still a very real question whether we ought to have the<br>
>>> >>>>> additional API surface implied by areSame, or wether we should<br>
>>> collapse<br>
>>> >>>>> it with ===.<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> To spell this out (because I had to think about it for a second):<br>
>>> ===<br>
>>> >>>>> will be derived from<br>
>>> >>>>> <=>,<br>
>>> >>>>> but also becomes default implementation for ==, which remains open<br>
>>> for<br>
>>> >>>>> customization.<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> I was imagining roughly this (untested):<br>
>>> >>>>><br>
>>> >>>>> /// Two references are identical if they refer to the same<br>
>>> >>>>> /// instance.<br>
>>> >>>>> ///<br>
>>> >>>>> /// - Note: Classes with a more-refined notion of “identical”<br>
>>> >>>>> /// should conform to `Identifiable` and implement `===`.<br>
>>> >>>>> func ===(lhs: AnyObject, rhs: AnyObject) -> Bool {<br>
>>> >>>>> ObjectIdentifier(lhs) == ObjectIdentifier(rhs)<br>
>>> >>>>> }<br>
>>> >>>>><br>
>>> >>>>> /// Supports testing that two values of `Self` are identical<br>
>>> >>>>> ///<br>
>>> >>>>> /// If `a` and `b` are of type `Self`, `a === b` means that<br>
>>> >>>>> /// `a` and `b` are interchangeable in most code. A conforming<br>
>>> >>>>> /// type can document that specific observable characteristics<br>
>>> >>>>> /// (such as the `capacity` of an `Array`) are inessential and<br>
>>> >>>>> /// thus not to be considered as part of the interchangeability<br>
>>> >>>>> /// guarantee.<br>
>>> >>>>> ///<br>
>>> >>>>> /// - Requires: `===` induces an equivalence relation over<br>
>>> >>>>> /// instances.<br>
>>> >>>>> /// - Note: conforming types will gain an `==` operator that<br>
>>> >>>>> /// forwards to `===`.<br>
>>> >>>>> /// - Note: Types that require domain-specific `==`<br>
>>> >>>>> /// implementations with different semantics (e.g. floating<br>
>>> >>>>> /// point) should define a more-specific overload of `==`,<br>
>>> >>>>> /// which will be used in contexts where the static type is<br>
>>> >>>>> /// known to the compiler.<br>
>>> >>>>> /// - Note: Generic code should usually use `==` to compare<br>
>>> >>>>> /// conforming instances; that will always dispatch to `===`<br>
>>> >>>>> /// and will be unaffected by more specific overloads of<br>
>>> >>>>> /// `==`.<br>
>>> >>>>> protocol Identifiable { // née Equatable name is negotiable<br>
>>> >>>>> func ===(_: Self, _: aSelf) -> Bool<br>
>>> >>>>> }<br>
>>> >>>>><br>
>>> >>>>> /// Default definition of `==` for Identifiable types.<br>
>>> >>>>> func ==<T: Identifiable>(lhs: T, rhs: T) -> Bool {<br>
>>> >>>>> return lhs === rhs<br>
>>> >>>>> }<br>
>>> >>>>><br>
>>> >>>>> /// Conforming types have a default total ordering.<br>
>>> >>>>> ///<br>
>>> >>>>> /// If `a` and `b` are of type `Self`, `a <=> b` means that<br>
>>> >>>>> /// `a` and `b` are interchangeable in most code. A conforming<br>
>>> >>>>> /// type can document that specific observable characteristics<br>
>>> >>>>> /// (such as the `capacity` of an `Array`) are inessential and<br>
>>> >>>>> /// thus not to be considered as part of the interchangeability<br>
>>> >>>>> /// guarantee.<br>
>>> >>>>> ///<br>
>>> >>>>> /// - Requires: `<=>` induces a total ordering over<br>
>>> >>>>> /// instances.<br>
>>> >>>>> /// - Requires: the semantics of `<=>` are consistent with<br>
>>> >>>>> /// those of `===`. That is, `(a <=> b) == .equivalent`<br>
>>> >>>>> /// iff `a === b`.<br>
>>> >>>>><br>
>>> >>>>> For floating point, I'd hope that `a === b` if `(a <=> b) == .same`<br>
>>> >>>>> *but not iff*. This is to satisfy IEEE 754: "Comparisons shall<br>
>>> ignore the<br>
>>> >>>>> sign of zero (so +0 = −0)".<br>
>>> >>>>><br>
>>> >>>>> /// - Note: conforming types will gain `<`, `<=`, `>`, and `>=`<br>
>>> >>>>> /// operators defined in terms of `<=>`.<br>
>>> >>>>> /// - Note: Types that require domain-specific `<`, etc.<br>
>>> >>>>> /// implementations with different semantics (e.g. floating<br>
>>> >>>>> /// point) should define more-specific overloads of those<br>
>>> >>>>> /// operators, which will be used in contexts where the<br>
>>> >>>>> /// static type is known to the compiler.<br>
>>> >>>>> /// - Note: Generic code can freely use `<=>` or the traditional<br>
>>> >>>>> /// comparison operators to compare conforming instances;<br>
>>> >>>>> /// the result will always be supplied by `<=>`<br>
>>> >>>>> /// and will be unaffected by more specific overloads of<br>
>>> >>>>> /// the other operators.<br>
>>> >>>>> protocol Comparable : Identifiable {<br>
>>> >>>>> func <=> (lhs: Self, rhs: Self) -> Ordering<br>
>>> >>>>> }<br>
>>> >>>>><br>
>>> >>>>> /// Default implementations of `<`, `<=`, `>`, and `>=`.<br>
>>> >>>>> extension Comparable {<br>
>>> >>>>> static func <(lhs: Self, rhs: Self) -> Bool {<br>
>>> >>>>> return (lhs <=> rhs) == .ascending<br>
>>> >>>>> }<br>
>>> >>>>> static func <=(lhs: Self, rhs: Self) -> Bool {<br>
>>> >>>>> return (rhs <=> lhs) != .ascending<br>
>>> >>>>> }<br>
>>> >>>>> static func >(lhs: Self, rhs: Self) -> Bool {<br>
>>> >>>>> return (lhs <=> rhs) == .descending<br>
>>> >>>>> }<br>
>>> >>>>> static func >=(lhs: Self, rhs: Self) -> Bool {<br>
>>> >>>>> return (rhs <=> lhs) != .descending<br>
>>> >>>>> }<br>
>>> >>>>> }<br>
>>> >>>>><br>
>>> >>>>> I like this idea. If we keep === as a separate thing, now users<br>
>>> have 3<br>
>>> >>>>> “opportunities” to define<br>
>>> >>>>> equality. The must be few, if any, use cases for this.<br>
>>> >>>>><br>
>>> >>>>> Would love to see if anyone on the list can give us an example.<br>
>>> >>>>> Otherwise we should make<br>
>>> >>>>> areSame === again™!<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> Daniel Duan<br>
>>> >>>>> Sent from my iPhone<br>
>>> >>>>><br>
>>> >>>>> On Jul 21, 2016, at 6:32 PM, Robert Widmann via swift-evolution<br>
>>> >>>>> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>>><br>
>>> >>>>> wrote:<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> On Jul 21, 2016, at 6:19 PM, Xiaodi Wu<br>
>>> >>>>> <<a href="mailto:xiaodi.wu@gmail.com">xiaodi.wu@gmail.com</a><br>
>>> >>>>> <mailto:<a href="mailto:xiaodi.wu@gmail.com">xiaodi.wu@gmail.com</a> <<a href="mailto:xiaodi.wu@gmail.com">xiaodi.wu@gmail.com</a>>>><br>
>>> >>>>> wrote:<br>
>>> >>>>><br>
>>> >>>>> This is nice. Is `areSame()` being proposed because static `==` is<br>
>>> >>>>> the status quo and you're trying to make the point that `==` in the<br>
>>> >>>>> future need not guarantee the same semantics?<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> Yep! Equivalence and equality are strictly very different things.<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> Nit: I think the more common term in stdlib would be<br>
>>> >>>>> `areEquivalent()`. Do you think `same` in that context (independent<br>
>>> >>>>> of the word "ordering") might erroneously suggest identity?<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> There is room for improvement here. Keep ‘em coming.<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> On Thu, Jul 21, 2016 at 8:11 PM, Robert Widmann via<br>
>>> >>>>> swift-evolution<br>
>>> >>>>> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>>><br>
>>> >>>>> wrote:<br>
>>> >>>>> Hello Swift Community,<br>
>>> >>>>><br>
>>> >>>>> Harlan Haskins, Jaden Geller, and I have been working on a<br>
>>> >>>>> proposal to clean up the semantics of ordering relations in the<br>
>>> >>>>> standard library. We have a draft that you can get as a gist.<br>
>>> >>>>> Any feedback you might have about this proposal helps - though<br>
>>> >>>>> please keeps your comments on Swift-Evolution and not on the gist.<br>
>>> >>>>><br>
>>> >>>>> Cheers,<br>
>>> >>>>><br>
>>> >>>>> ~Robert Widmann<br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> _______________________________________________<br>
>>> >>>>> swift-evolution mailing list<br>
>>> >>>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>><br>
>>> >>>>> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a>><br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> _______________________________________________<br>
>>> >>>>> swift-evolution mailing list<br>
>>> >>>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>><br>
>>> >>>>> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a>><br>
>>> >>>>><br>
>>> >>>>> _______________________________________________<br>
>>> >>>>> swift-evolution mailing list<br>
>>> >>>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>><br>
>>> >>>>> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a>><br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> --<br>
>>> >>>>> Dave<br>
>>> >>>>><br>
>>> >>>>> _______________________________________________<br>
>>> >>>>> swift-evolution mailing list<br>
>>> >>>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>>>><br>
>>> >>>>> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a>><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a>>><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a>><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a>>>><br>
>>> >>>>><br>
>>> >>>>> _______________________________________________<br>
>>> >>>>> swift-evolution mailing list<br>
>>> >>>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>>><br>
>>> >>>>> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a>><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a>>><br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> --<br>
>>> >>>>> Dave<br>
>>> >>>>><br>
>>> >>>>> _______________________________________________<br>
>>> >>>>> swift-evolution mailing list<br>
>>> >>>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>>><br>
>>> >>>>> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a>><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a>>><br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> --<br>
>>> >>>>> Dave<br>
>>> >>>>> _______________________________________________<br>
>>> >>>>> swift-evolution mailing list<br>
>>> >>>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>><br>
>>> >>>>> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a>><br>
>>> >>>>><br>
>>> >>>>> _______________________________________________<br>
>>> >>>>> swift-evolution mailing list<br>
>>> >>>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <mailto:<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a> <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>><br>
>>> >>>>> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>> <<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a>><br>
>>> >>>>><br>
>>> >>>>> _______________________________________________<br>
>>> >>>>> swift-evolution mailing list<br>
>>> >>>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> --<br>
>>> >>>>> Dave<br>
>>> >>>>><br>
>>> >>>>> _______________________________________________<br>
>>> >>>>> swift-evolution mailing list<br>
>>> >>>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>>> _______________________________________________<br>
>>> >>>>> swift-evolution mailing list<br>
>>> >>>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>>> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>>><br>
>>> >>>>><br>
>>> >>>> _______________________________________________<br>
>>> >>>> swift-evolution mailing list<br>
>>> >>>> <a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
>>> >>>> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
>>> >>>><br>
>>> >>>><br>
>>> >>><br>
>>> >><br>
>>> >><br>
>>><br>
>>> --<br>
>>> Dave<br>
>>><br>
>><br>
>><br>
<br>
</div></div><span class="HOEnZb"><font color="#888888">--<br>
Dave<br>
</font></span></blockquote></div><br></div></div>