Nine Ways to Do Inheritance in Rust, a Language Without Inheritance

(medium.com)

43 points by pjmlp2 days ago

3 comments

iTokio2 hours ago
I almost never use inheritance beside using some kind of interfaces/traits to declare a contract.However, the only time where I’m missing code/data reuse through inheritance is with GUI. Some mostly flat hierarchies of widgets are really powerful ways to declare and compose UI components with shared behaviors.In rust, the DX for GUI components is always lacking compared to web, C#. With maybe the exception of Slint which is really not Rust anymore.Is there a way to have good DX for GUI components in Rust?
- aabhay1 hour ago
 If you want to get inspired by good component DX, try looking at Bevy, the game engine.But essentially it comes down to traits, newtypes/enum variants, and macros.
pdpi4 hours ago
Cool catalogue, but it had nothing to do with inheritance. It’s more “nine ways to do polymorphism-adjacent things using ad-hoc polymorphism (“traits”) instead of subtype polymorphism (‘inheritance’)”
- nextaccountic3 hours ago
 Just like you can do OO in any language - for example, you can do OO like C (or at least that's what GTK folks believe), Rust already has most runtime mechanisms to pretty much implement inheritance in a library or a coding pattern (as opposed to a language feature)For a long time the most important thing missing was a better story around upcasting, but Rust 1.86 implemented the usual child-to-parent upcasting [0] expected in OO (with the Any trait doing the parent-to-child downcasting [1] in a way that's less error prone than most OO languages actually)Also note that Firefox and Servo were a early proponents of getting more OO into Rust (I guess that's because they need to deal with the DOM? Not sure). Which doesn't mean literally having classes and inheritance, but rather, language features that can emulate those when needed.Today I think the missing piece is fields in traits: a way for a vtable to store field offsets rather than just pointers to method; current practice is to add getters and setters to traits when needed (but that's "ugly"). Unfortunately discussion around this stalled [2][0]: <a href="https://blog.rust-lang.org/2025/04/03/Rust-1.86.0/#trait-upcasting" rel="nofollow">https://blog.rust-lang.org/2025/04/03/Rust-1.86.0/#trait-upc...</a>[1]: <a href="https://doc.rust-lang.org/std/any/index.html" rel="nofollow">https://doc.rust-lang.org/std/any/index.html</a>[2]: maybe the latest one is <a href="https://internals.rust-lang.org/t/fields-in-traits/6933/" rel="nofollow">https://internals.rust-lang.org/t/fields-in-traits/6933/</a> but idk
- Animats2 hours ago
 Yes. The polymorphism isn't bad. It's the inheritance of data that's the problem.Rust traits can't have associated data. That's the big difference from objects.It's also hard to have a parent-child relationship where the child can find the parent. That takes much fooling around with wordy combos of Rc, Weak, upgrade, etc.This makes it hard to convert C++ programs, and C++ programmers, to Rust. It's quite possible to write 100% safe code under Rust's constraints, but it takes a major rethink from C++.
zozbot2343 hours ago
Much of this post seems to focus on interface inheritance via traits, which is a well-known feature of Rust. It's weird though that it completely misses the generic typestate pattern, which is pretty unique to Rust as far as it goes and can be quite fairly described as OOP implementation inheritance in a type-theoretic trench coat.