Is `None` returned from `partial_cmp` supposed to only signify `NaN`?

[jbe]

@steffahn

@RedDocMD

PartialOrd in Rust has the exact same meaning as in mathematics when you say "partial order on a set", aka, an ordering exists only between some elements.

It’s a bit more general than that mathematical notion; admitted it’s still (mis-)documented as being about a “partial order”. I’ve semi-recently participated in a way too long discussion about those points; I don’t fully remember the outcome, […]

Without having read the context of this thread, I would like to quote my point on whether:

@RedDocMD

PartialOrd in Rust has the exact same meaning as in mathematics […]

My p.o.v. was this one:

@jbe

PartialOrd kinda describes a (strict) partial order, but the corresponding non-strict partial order isn't reflected by Rust's comparison operators (except < and >).

And:

@jbe

I'm not really a mathematician, but when I read PartialOrd, I automatically assume "oh, that's a partial order" (as I have worked with partial orders in the past). I would think so even if the docs didn't use the term, but just because the trait is named "PartialOrd". It also helps me to understand that I can use PartialOrd to implement a partial order, but it will confuse me if I'm suddenly surprised by >= and <= not acting accordingly. (And I was very confused from the discussion of this topic .)