Why is it not possible to implement Ord for a different Rhs type? It is possible with PartialOrd , so I assume it has something to do with the difference between the two? Is it because different types should not have a total ordering defined between each other? If so, why not?

I don't know the original reason, but the default implementations of Ord::{min,max} (Rust 1.21) and Ord::clamp (Rust 1.50) can only work with Self arguments for comparison.

So it sounds like more of an oversight, right? Because I can't see a reason why that should be prohibited.. Is it possible to amend the trait definition in this way, with a type parameter defaulting to Self, while remaining backwards compatible?

I believe it's because implementing Ord requires also implementing Eq, which doesn't have an Rhs type parameter to ensure symmetry (a == b implies b == a)

[image] mankinskin: So it sounds like more of an oversight, right? I sketched out some history as best as I could tell here.

But symmetry could be ensured even with something like this, on the type level at least: trait Eq<Rhs = Self> where Rhs: Eq<Self> + ?Sized { fn eq(&self, other: &Rhs) -> bool; } ( test )

So its not an oversight, but just hasn't been implemented yet, if I understand correctly.

Well, I doubt someone accidentally removed the generics in the stabilization PR, but I can't really speak for anyone else. It is technically a non-implemented [1] part of an accepted [2] RFC. I have no idea what the lib team would think about adding it today, or if they'd care that it's technicall…

Implement Ord to compare different types

help

quinedot March 17, 2022, 9:50pm 5

I sketched out some history as best as I could tell here.

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Implement Ord to compare different types

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