> Rust: I'm not afraid to admit it - Rust is just too complicated for use as an aging and cranky solo developer. I'm nearly 51 and currently learning Rust. The first 10 hours of it were horribly slow, but it isn't as steep of a learning curve as Optimal Control Theory.
Learning curve is straight up for many with the borrow checker, but once you are over that hump, and it comes pretty quick for most, Rust is no harder than any other language.
In my experience, it depends heavily on the kind of thing you're writing. I could write some small programs in it, no problem: a rather complex, text-based calculator was easy and elegant to write with function arguments, a game server monitor, some tools for a cryptography course, an FFT analyzer that reads from WAV or AIFF, etc. Then I tried to port my rather efficient Earley parser (https://en.wikipedia.org/wiki/Earley_parser) from C. Constructing the item set efficiently wasn't that hard, but constructing the forest (set of syntactic trees) was. In C, it was basically free by using some pointer sharing, but I couldn't get that done in Rust. Perhaps there's some clever trick I couldn't think of, but I couldn't get it anywhere near C's speed. And since the ultimate goal of that parser includes further memory shenanigans (unification of results yielded by the rules), I dropped the project.
At my job, I'm writing in Go. I fairly sure I could easily port the C code to that. It would probably run a bit slower, but the algorithm and data structures would be readable, and extendable.
So: it depends.