Document details of Ord for Tuples, Option, Result, others?

[Havvy]

In #rust, we had a user ask if Ord for (A, B, C) checks left to right or right to left. (It's left to right.)

This should be documented in the stdlib docs somewhere.

Similarly, should be documented for other enums such as Option (Some(T) > None) and Result (uhh, didn't check) and possibly others where it could be something different.

[durka]

Definitely seems like it can't be left undocumented. Changing the sort order of Option in a future release would be a breaking change.

The sort order of derived ordering is mentioned in the docs: https://doc.rust-lang.org/std/cmp/trait.PartialOrd.html#derivable (same text is at Ord)

Would you want it somewhere else as well?

[Havvy]

@durka Even if the impl for these is via a #[derive], that information is disconnected from the actual impls when you look at the docs. And when we look at the impls, we don't see the declaration order of the struct members.

[QuietMisdreavus]

Documenting derived traits is a duplicate of #44118.

Tuples, on the other hand, don't get their traits via derive. All those traits are applied via a macro, so it's possible to add docs there without extending the language to add arbitrary attributes to a derive.

[saleemjaffer]

@steveklabnik @estebank I would like to take this up.

[poliorcetics]

Is there still something to do about this issue ? If yes, I would like to do it, but I see tuples have been documented and from what I understand the rest is apparently not needed.

[bertptrs]

The ordering for Option and Result is documented through a small note in the Derivable section:

When derived on enums, variants are ordered by their discriminants. By default, the discriminant is smallest for variants at the top, and largest for variants at the bottom. Here’s an example:

And then it lists two examples. The ordering for both Result and Option is indeed simply derived so that covers that. However that fact could be considered an implementation detail, so I think it's still good to mention it explicitly on the relevant pages.

The sort order for tuples is defined in the tuple documentation and I think that should cover it.

[Dylan-DPC]

Closing this as the documentation now mentions this albeit in different places