[darksaints]

There are many calls for, and proposals to include, some form of inheritance in Rust. Among other things, people have found that Rust is poorly suited to modeling HTML/XML hierarchies, retained mode GUIs, industrial simulations, code specialization, and some forms of video games. Inheritance is a missed feature.

What is clear to me is that Rust does incredibly well without it, but wouldn't be hurt by having it. Most of the egregious sins of OOP are mitigated by having far better abstractions available in Rust. ML-style modules, ADTs with pattern matching, type classes, first class functions, etc. Much like scala, if you give them capable FP, OOP stops being abused and starts being used appropriately.

[jwatte]

Aggregations and interfaces cover 99%of what you need. Implementation inheritance and virtual variation points create too tight coupling to be workable for evolving systems.

[saosebastiao]

Maybe 99% of what you need, but more like 70% of what I need. I'm not sure what you mean by aggregations, but I design industrial simulations relatively frequently and I've seen the suggestions for replacing inheritance with composed typeclasses and they are not even close to a true alternative. Rust's current troubles with GUI development would suggest the same pattern there too.

[zeptomu]

Can you elaborate on that? What's an industrial simulation (compared to a "regular" simulation) and why do you like to solve it with inheritance?

[saosebastiao]

An industrial simulation, in my context, is modeling the stateful flow of things through industrial processes. It typically involves millions of instances of thousands of types. There are typically much fewer very well defined processes, most of which would be trivial to implement with a simple impl trait with default methods. But some require stateful members in order to implement a default behavior, but Rust traits do not have fields/members, just functions.

Rust traits and Scala traits (or abstract classes) are more or less equivalent with this one exception. I was just pointed to a proposal that would allow for this in Rust, but it is not yet implemented [0]. Essentially, you would be able to define type members, and then "link" them to a member of the struct/enum that is being "impl"-ed. While ergonomically not quite the same as scala, it is effectively the same as inheriting an abstract class with a constructor parameter.

[0] https://github.com/rust-lang/rfcs/pull/1546

[eru]

There was an interesting talk about industrial simulations at the International Conference on Functional Programming this year.

(The gist was that avoiding mutation and keeping everything purely functional allowed them to roll back and forth in time with no problem, or try out multiple different futures. That's somewhat orthogonal to inheritance.)