The frustrating part was concatenation, it was surprisingly annoying to combine a few strings and an int into a single string.
let cat = format!("{}{}{}", s1, s2, n);I personally only tend to use + when there's two or maybe three things at most, in any language, and then switch to an API like this if it exists for more complex things, no matter the language. I find it much easier to read. YMMV.
(And you can use + in Rust, but you'd have to call .to_string() on the integer first)
Best intro documentation of any language I have tried to learn recently.
EDIT for those who havent seen it: https://doc.rust-lang.org/book/