[swift-evolution] [Proposal draft] Enhanced floating-point protocols

Stephen Canon scanon at apple.com
Fri Apr 15 11:58:26 CDT 2016

> On Apr 15, 2016, at 9:52 AM, Stephan Tolksdorf via swift-evolution <swift-evolution at swift.org> wrote:
> but the documentation for Equatable and Comparable states that == and < must implement an equivalence relation and a strict total order, which is incompatible with the default IEEE-754 implementation of these operators when NaN values are involved. How do you resolve this conflict?

That’s a documentation bug; it should be relaxed by appending something like “… on non-exceptional values.”

I’ll quote Dave A. to put it a bit more formally:

> To be clear, the semantic conformance of floating point types to Comparable depends on treating NaN as a "singular value”, i.e. outside the domain of valid arguments to < for the purposes of Comparable.  That doesn’t mean we can’t nail down what < does for floating point types when it does get a NaN.

– Steve
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