this post was submitted on 19 Mar 2024
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Programming
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I'm still onboard with rust as being better than C, however...
My understanding is that it is considerably harder to correctly write unsafe rust than it is to correctly write c, because if you accidentally violate any of safe rust's guaranteed invariants in an unsafe block, things go bananas.
That's true in C as well, though. This is what people mean when they say things like "undefined behavior can result in time travel".
The difference is twofold:
unsafecode are not completely formalized yet. This means that there are open questions about whether particularly complex patterns in unsafe code will be guaranteed by future versions of the compiler to be sound. Conversely, the C and C++ spec are generally sufficient to determine whether any particular piece of code has undefined behavior, even if actually analyzing it to find out is not possible automatically using existing static analysis tools.Yes Rust is harder to write than C, that's basically by design as it's due to the statically guaranteed memory safety. That's pretty magical. C doesn't have that and neither does C++ even with smart pointers and such. Rusts unsafe keyword is poorly named, what it actually does is tell the compiler that you the programmer guarantee Rusts rules are upheld within the unsafe block.
For example
That is a global, that's incredibly hard to impossible to statically prove it's safely done, so you have to do it in an unsafe block. So you violating Rusts rules within an unsafe block is actually using the unsafe block wrong. That's not what it's for
I remember watching a video of someone writing C code and making the same thing in unsafe rust. While the C code worked just fine the rust code had UB in it and was compiled to a different set of instructions.
Unsafe rust expects you to uphold the same guarantees that normal rust does and so the compiler will make all the same optimisations it would if the code wasn't unsafe and this caused UB in the example rust code when optimised for performance. It worked just fine on the debug build, but that's UB for you.
I would totally argue with this. Rust is way easier to write than C
I'd probably say it depends but I'm no Rust expert and I have no direct experience with C (though quite familiar with C++).
Basically I'd expect writing C to be easy, but not safe. IE you can quickly and easily write C that compiles but has runtime issues. Rust for the most part will catch everything but logic issues during/before compilation meaning once the program runs you'll have very high confidence in it's runtime behavior leading to time spent "fighting the compiler" instead of figuring out wtf is going wrong at runtime.
I think primarily I don't really care to argue about if it's harder to write or not since it doesn't really matter. I think the pros Rust provides are worth all it's cons
So what's "easy" about it then? Just getting something to compile? That's not a very good measure of "easyness".
I agree for the most part, but writing data structures with shared mutable state can be a total pain in Rust.
How so? That's like, the thing that makes rust awesome to write.
It's hard to get those kinds of data structures through the borrow checker.
Try writing a doubly linked list.
It's because it's hard to make them correct. It's not any harder to write it in rust than in C. Just C lets you do it wrong
That's not right.
Try and write a mutable doubly linked list in Rust and you will find that it's problematic for the borrow checker.
Search online and you will find solutions that work around this using 'RefCell' (to delegate mutable borrows to runtime), or raw pointers with 'unsafe'.
That depends a lot on how you define "correct C".
It is harder to write rust code than C code that the compiler will accept. It is IMHO easier to write rust code than to write correct C code, in the sense it only uses well defined constructs defined in the C standard.
The difference is that the rust compiler is much stricter, so you need to know a lot about details in the memory model, etc. to get your code past the compiler. In C you need the same knowledge to debug the program later.