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

[Dmitri Gribenko]

On Fri, Jul 22, 2016 at 2:13 AM, Pyry Jahkola via swift-evolution
<swift-evolution at swift.org> wrote:
> 5. Will it be considered "ok" to define a type for which `T.areSame(a, b) == true` but `a != b`? An obvious example would be Double.nan, so I assume the answer is a resounding yes.

Yes, because `==` is not a protocol requirement of Equatable, so it
can have domain-specific semantics.

> 6. Similarly, will it be "ok" to define a type for which `T.areSame(a, b) == false` but `a == b`? One possible example could be the comparison of `-0.0 <=> +0.0`. Should those be `.same` or not?
>
> 7. What, in fact, is the proposed total order for the stdlib's floating-point types?

The IEEE 754 definition.

https://github.com/apple/swift/blob/f318fe853d7898246db24d501f1ddc03c9eb8651/stdlib/public/core/FloatingPoint.swift.gyb#L855

Dmitri

-- 
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
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