That's my personal opinion after I've learned it and read Klabnik's book. I'm aware that other people's mileage differs. I'm listing a few reasons below.
- Overall too complex
- Wrong philosophy: demanding the user to solve problems instead of solving problems for the user
- Trying to provide infinite backwards compatibility with crates, which leads to hidden bitrot
- Slow compilation times
- Claims to be "safe" but allows arbitrary unsafe code, and it's everywhere.
- Adding features to fix misfeatures (e.g. all that lifetime cruft; arc pointers) instead of fixing the underlying problem
- Hiding implementations with leaky abstractions (traits)
- Going at great length to avoid existing solutions so users re-invent it (e.g. OOP with inheritance; GC), or worse, invent more complex paradigms to work around the lack (e.g. some Rust GUI efforts; all those smart pointer types to work around the lack of GC)
- A horrendous convoluted syntax that encourages bad programming style: lot's of unwrap, and_then, etc. that makes programs hard to read and audit.
- Rust's safe code is not safe: "Rust’s safety guarantees do not include a guarantee that destructors will always run. [...] Thus, allowing mem::forget from safe code does not fundamentally change Rust’s safety guarantees."
It already has similar complexity and cognitive demands as C++ and it's going to get worse. IMHO, that's also why it's popular. Programmers love shitty languages that allow them to show off. Boring is good.
