Rust will try to relax the orphan rule (= Julia's type piracy)

xiaoxi · May 14, 2024, 6:13pm

Rust has set a goal for this year to experiment with ways to relax the orphan rule.

rust-lang/rust-project-goals/blob/main/src/2024h2/Relaxing-the-Orphan-Rule.md

# Relaxing the Orphan Rule

| Metadata | |
| --- | --- |
| Owner(s) | |
| Teams | *lang* |
| Status | WIP |

## Motivation

Relax the orphan rule, in limited circumstances, to allow crates to provide
implementations of third-party traits for third-party types. The orphan rule
averts one potential source of conflicts between Rust crates, but its presence
also creates scaling issues in the Rust community: it prevents providing a
third-party library that integrates two other libraries with each other, and
instead requires convincing the author of one of the two libraries to add
(optional) support for the other, or requires using a newtype wrapper. Relaxing
the orphan rule, carefully, would make it easier to integrate libraries with
each other, share those integrations, and make it easier for new libraries to
garner support from the ecosystem.

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I wonder if Julia could learn something from Rust’s experiment in relaxing the orphan rule.

Benny · May 14, 2024, 7:29pm

The overall orphan rule does vaguely sound like preventing type piracy, but is this particular relaxation for integrating 2 libraries really analogous to type piracy? While it’s more ideal to update one of the packages, I don’t immediately see dispatch issues with taking a type from package A and implementing a method from package B for it, unless one of those packages or its extension already imports the other. The concept of extensions itself suggests to me that arbitrarily mixing otherwise unrelated packages in a 3rd module is safe, though a 4th can easily interfere with the 3rd.

mbauman · May 14, 2024, 7:52pm

As I understand it, Rust will throw an error if you try to implement an orphan like this. That makes it a significantly different sort of thing.