[swift-evolution] [Draft][Proposal] Formalized Ordering

Matthew Johnson matthew at anandabits.com
Fri Jul 22 09:54:27 CDT 2016

> On Jul 22, 2016, at 9:48 AM, Karl via swift-evolution <swift-evolution at swift.org> wrote:
>> On 22 Jul 2016, at 03:32, Robert Widmann via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> On Jul 21, 2016, at 6:19 PM, Xiaodi Wu <xiaodi.wu at gmail.com <mailto:xiaodi.wu at 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.
> As I understand it:
> -> what we call “Equatable” today checks for equivalence. For value types, equivalent is the same as equality (that’s why they are values - two instances with the same data are indistinguishable).
> -> For reference types, we have an instance-equality operator (===) which checks for what I believe you mean by equality.

Except that the standard floating point == is not an equivalence relation.  I’m not sure if the distinction introduced by this proposal is solely due to that or if there are other example use cases for making a distinction.

> Karl
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