matklad

Rust Course Retrospective

It was the last week of the Rust course at Computer Science Center. This post is my experience report from teaching this course.

Materials

Note that the course is in Russian :-)

Course slides are available under CC-BY at https://github.com/matklad/rust-course. See the sibling post if you want to learn more about how the slides were made (TL;DR: Asciidoctor is better than beamer, Google Docs, slides.com, reveal.js, remark).

High-quality recordings of lectures are available on YouTube (full playlist):

The homework is not available, but it was based on the Ray Tracing in One Weekend book.

Good Parts

Teaching is hard, but very rewarding. Teaching Rust feels especially good because the language is very well designed and the quality of the implementation is great. Overall, I don’t feel like this was a particularly hard course for the students. In the end most of the folks successfully completed all assignments, which were fairly representative of the typical Rust code.

Hard Parts

There were one extremely hard topic and one poorly explained topic.

The hard one was the module system. Many students were completely stumped by it. It’s difficult to point out the specific hard aspect of the current (Rust 2018) module system: each student struggled in their own way.

Here’s a selection of points of confusion:

  • you don’t need to wrap contents of foo.rs in mod foo { …​ }

  • you don’t need to add mod lib; to main.rs

  • child module lives in the parent/child.rs file, unless the parent is lib.rs or main.rs

I feel like my explanation of modules was an OK one, it contained all the relevant details and talked about how things work under the hood. However, it seems like just explaining the modules is not enough: one really needs to arrange a series of exercises about modules, and make sure that all students successfully pass them.

I don’t think that modules are the hardest feature of the language: advanced lifetimes and unsafe subtleties are more difficult. However, you don’t really write mem::transmute or HRTB every day, while you face modules pretty early.

The poorly explained topic was Send/Sync. I was like "compiler infers Send/Sync automatically, and after that your code just fails to compile if it would had a data race, isn’t Rust wonderful?". But this misses the crucial point: in generic code (both for impl T and dyn T), you’ll need to write : Sync bounds yourself. Of course the homework was about generic code, and there were a number of solutions with (unsound) unsafe impl<T> Sync for MyThing<T> :-)

Annoying Parts

It’s very hard to google Rust documentation at the moment, because google links you to redirect stubs of the old book, which creates that wierd feeling that you are inside of a science-fiction novel. I know that the problem is already fixed, and we just need to wait until the new version of the old book is deployed, but I wish we could have fixed it earlier.

Editions are a minor annoyance as well. I’ve completely avoided talking about Rust 2015, hoping that I’ll just teach the shiny new thing. But of course students google for help and get outdated info.

  • many used extern crate syntax

  • dyn in dyn T was sometimes omitted

  • there was a couple of mod.rs

Additionally, several students somehow ended up without edition = "2018" in Cargo.toml.

Discussion on /r/rust.