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

[Brent Royal-Gordon]

> On Jul 21, 2016, at 6:11 PM, Robert Widmann via swift-evolution <swift-evolution at 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.

My thoughts on this are not yet fully formed, but I have a couple questions concerning `isSame(_:_:)` and `==`:

* Should calls like `index(of:)` and `split(separator:)` use `==` or `isSame(_:_:)`?

* Should `Hashable` use `==` or `isSame(_:_:)`?

* Do we know of any use cases where a type conforms to `Equatable` but not `Comparable` and needs separate `isSame(_:_:)` and `==` operators? 

Essentially, I'm wondering if we can leave `Equatable`'s definition alone and only change `Comparable` to require `<=>`, with a generic operator to provide a default `==` which uses `<=>`.

-- 
Brent Royal-Gordon
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