[swift-dev] Rationalizing FloatingPoint conformance to Equatable

Jonathan Hull jhull at gbis.com
Fri Oct 20 01:22:30 CDT 2017

+1 for trapping unless using &==.  In the case of ‘Float?’ we could also map to nil.

This is probably a more appropriate discussion for evolution though...

> On Oct 19, 2017, at 9:48 PM, Brent Royal-Gordon via swift-dev <swift-dev at swift.org> wrote:
>> On Oct 19, 2017, at 4:29 PM, Xiaodi Wu via swift-dev <swift-dev at swift.org <mailto:swift-dev at swift.org>> wrote:
>> D) Must floating-point IEEE-compliant equivalence be spelled `==`?
>> In my view, this is something open for debate. I see no reason why it cannot be migrated to `&==` if it were felt that `==` *must* be a full equivalence relation. I believe this is controversial, however.
> I actually got partway through writing up a pitch on this yesterday, but my opinion is that NaNs are so exceptional, and so prone to misuse, that we ought to treat them like integer arithmetic overflows: trap when they're detected, unless you use an `&` variant operator which indicates you know what you're doing.
> I strongly suspect that, in practice, most float-manipulating code is not prepared to handle NaN and will not do anything sensible in its presence. For example, Apple platforms use floating-point types for geometry, color components, GPS locations, etc. Very little of this code will do anything sensible in the presence of a NaN. Arguably, it'd be better to exclude them through the type system, but I don't think that's a realistic possibility—we would need to have done that in a more source-break-friendly era. But that doesn't have to mean we're completely stuck.
> -- 
> Brent Royal-Gordon
> Architechies
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