Why `sort()` need `T` to be `Ord`?

[jdahlstrom]

@tczajka

Maybe you could argue that f32 doesn't really have a partial order (I would say it's close enough), but even if so, doesn't mean the trait is not a partial order trait, it's just that impl PartialOrder for f32 doesn't do the right thing.

Which is funny, of course, given that AFAIK the whole reason PartialOrd exists is the IEEE 754 floating-point semantics. Is there even precedence for objects that behave like IEEE floats in mathematics? Are they weird enough to not match any more-or-less commonly used terminology?

NULL in SQL has similar semantics but seems more sane in that it embraces true three-valued logic: its "PartialEq" actually returns "Option<bool>" in Rust terms. So NULL == NULL is neither true nor false, it is itself NULL, as in unknown, just like NULL < NULL.