I have this niggling feeling like I still haven't really "learned" Rust. I realized today that this feeling is wrong—I know enough Rust to build whatever I want, which should be the rubric anyone uses to decide they "know" something or not.
I know enough about cooking to prepare any dish I could imagine wanting to prepare—is that enough, or have I still not "learned" how to cook? (After about 10 years of persistent study, I finally feel comfortable saying "I can cook".)
I've decided I don't want to "learn" something for the label. I know enough. I know Rust.
A note specific to Rust
What's made this transition (from "learning" to "learned") harder with Rust, I think, is that Rust has an intense learning curve up front, and then almost completely gets out of your way. Once you've learned how to tell the language your plan, it quickly gets out of the way, exposing nothing but the problem you're trying to solve. Because I'm using Rust to solve problems I've never solved before, part of my hesitation in saying that I know Rust is that I haven't completely finished those projects. I haven't finished those projects because I haven't solved those problems, not because I'm unfamiliar with the tools I'm using.
Most languages conflate the two, and I appreciate those that have designed Rust otherwise.