1. Functions which convert a number to a string, where the target string is a byte buffer passed into the function as a pointer argument. This allows C developers to pass pointers to statically-sized arrays of bytes, which leads to buffer overflows. (Inb4 someone shows up with "but that's the programmer's fault for not using an array that's big enough".) Example: strcpy.
2. Functions which return pointers to static storage, which makes them thread-unsafe, and even in single-threaded cases is error-prone, when you call one such function multiple times in succession (aliasing). Example: gmtime.
Both cases are very prominent in the standard library.
If instead functions allocated memory dynamically, then they would avoid buffer overflow, because size would be handled exclusively within those functions, allocating as much memory as is needed, no more, no less; instead of forcing the programmer to worry about the size at every call-site. They could also be easily made thread-safe and less error-prone (eliminating aliasing), provided that the allocator is thread-safe.
Another issue with the first case is that it leads to uninitialised variables. Often a pattern of "bool NumToString(int n, char* dst, int size);" is employed instead of "Optional<std::string> NumToString(int n);". This invites the possibility of using "dst" without checking the return value, which says if the conversion succeeded. In this case dst is most likely uninitialised, and definitely incorrect. An "Optional<std::string>" solves both issues.
The C stdlib string API is rubbish of course (along with most other C stdlib APIs). But at least it's quite simple in C to ignore the stdlib (and use better 3rd-party-libs instead) without loosing important language features.
However we are slowly moving back into multi-processes as way to avoid in-process security exploits and improve overall application stability.
In these kind of scenarios, there is little that Rust type system can help regarding races in IPC.
When people do things you don't understand, don't just say that they're just doing it because it's fashionable. Sure, they might be — or they have their own reasons.
I use Rust in a couple of places outside of its original "systems programming" niche, where, yeah, I don't really need to track every allocation, I don't care about GC pauses, I don't need to ship one single binary, and the overhead of a runtime wouldn't bother me. Things like Web servers for side projects, or small scripts to do a task I need to automate.
However, I found that:
• The effort it took to bring Rust out of its niche, and the time it took to learn the domain-specific libraries for my use cases (Rocket for Web stuff; duct for shell script stuff) was less than I thought;
• The amount of knowledge I needed to retain to use a programming language effectively — the components of its standard library, common third-party helper libraries, how to navigate the documentation, how to fix mistakes, how to avoid traps and pitfalls, how to structure your program, how to handle differences between language versions — was much larger than I thought!
So I stick with Rust for non-systems tasks because the benefits outweigh the detriments for me.
(Granted, I was only able to do this because I already knew my way around the language and the borrow checker; if you already know, say, Python, you can make this exact same argument in reverse. But then you need to know how to wield Python for low-level programming as well as high-level programming.)
I read an article a few years ago called Java for Everything[1] (which was discussed here on HN[2]) that makes the same point, only with Java. If I had to pick an "everything language", I don't think it would be 2014-era Java, but the article did sell me on the benefits of having an "everything language" in the first place, and I feel the same benefits apply here with Rust.
[1]: https://www.teamten.com/lawrence/writings/java-for-everythin... [2]: https://news.ycombinator.com/item?id=8677556
Meanwhile in the real world: "I find myself hanging for long periods of time on borrow checker errors. One of the errors has stopped my progress dead for a week now, I swear it worked a week ago and then Rust decided that a borrow I was doing was no good." [2]
I do recall the steep learning curve and the frustrations with the borrow checker, but I haven’t had it impede me at all in probably two years now and I’m writing Rust most of the day every day.
Also, most of the knowledge I gained by learning to work with it is general knowledge that made me a better programmer, not specific knowledge of how to “work around” the borrow checker.
For anything else, it isn't worth the productivity drop of automated memory management (regardless in what form) coupled with value types.