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

Stephen Canon scanon at apple.com
Fri Jul 22 23:34:12 CDT 2016

> 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.

Boy, I take my wife out for a movie and come back to 50 new messages on SE.

I need to read the entire thread more carefully, but off the top of my head, I think that `-0 === +0` is False.  If we’re going to have an `isSame` / `isIdentical` / whatever it's called, I would expect it to imply substitutability.  Although -0 == +0, they are not equivalent when substituted:

- 1/(-0) != 1/0
- Float(-0).sign != Float(+0).sign
- etc

This probably then implies that `<=>` is not `.same` either.  I’ll read the rest of this and respond more completely tomorrow.

– Steve

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