Uncovered Intermediate Topics

Hi fellow Rustaceans!

As many of you know, I'm on a quest to expand Rust's teaching resources for intermediate topics — those that aren't for newcomers to the language, but also aren't so niche or advanced that they are only relevant to a small number of interested individuals (see Crust of Rust and Rust for Rustaceans). And I've been really happy to see a number of other Rustaceans putting out great resources on these topics over the past few years.

But I'm running low on potential topics. I doubt it's because all of the intermediate topics have already been covered, and suspect it's rather because I'm not on the "front lines" of the various Rust support channels (the support threads here, users.rlo, the Discord(s), StackOverflow, etc.), and thus am not as exposed to what questions come up without good resources to redirect users to.

So, here I am. I'd love to hear what you all see as intermediate topics that don't have decent teaching resources to point people to for explanations (whether videos, books, blogs, whatever). Hopefully collectively you have a trove of good candidate topics that I, or others, can cover, so that we can develop better teaching coverage for Rust as people "level up".

For some structure, let's limit suggestions to those that are 1) teachable in one long blog post or university-style lecture; 2) relevant to at least 1 in 5 Rust programmers; and 3) not already sufficiently covered between the Rust book and the std documentation. I'd also love one suggestion per top-level comment if possible to make things easier to discuss and track.

Moderators: I'd love to have this post be in contest mode if possible.