A garbage collected language does this automatically. Rust still requires thinking about and tracking memory lifecycles, but the borrow checker will complain and keep you from doing it wrong. That's why LLMs like Rust. It gives immediate feedback on what to fix. By-default constant reference parameters helps prevent major performance problems.
You're getting confused between lifetimes (the static analysis that prevents use after free and similar errors) and lifecycles (more commonly discussed under the heading of ownership) which determines when objects (and thus memory) are allocated and deallocated.
Ownership is automatic. You don't have to explicitly drop things when they go out of scope. (although the responsibility for that is split between the compiler and the library code).
Lifetimes are not automatic, but also have no effect on memory allocation. They are purely a static analysis path and you can make a functioning rust compiler that completely ignores lifetimes.
> You're getting confused between lifetimes (the static analysis that prevents use after free and similar errors) and lifecycles (more commonly discussed under the heading of ownership) which determines when objects (and thus memory) are allocated and deallocated.
Ownership is
That's a semantic distinction which does not matter in the point OP is making. And contrasting rust static approach to general GC.
True, but unsafe let's you conjure up any lifetime you want, or any lifetime necessary to satisfy the lifetime requirements in safe code. If you generously sprinkle pointer dereferences in unsafe code, you effectively disable the protection provided by the borrow checker – including in safe code – until you've checked and verified the correctness of all unsafe blocks.
Because it lets you constrain the parts that the compiler can’t check and has to trust you on. The alternative is either a langue that can’t do necessary things, or a language that can’t check what could be checked.
With unsafe, you’re telling the compiler “I’ve taken extra care to make sure that what I’m doing is safe and doesn’t break your rules” and the compiler can go ahead and assume that you don’t, in fact, break the rules, and therefore can verify everything else as if the rules never got broken.
In less safe languages, the entire program is “trust me, it’s safe”, while in rust only the parts flagged as unsafe are.
The point is that you should only use unsafe when 1. It’s absolutely necessary for functionality or performance and 2. You have verified and are very certain that the code is correct.
Yes, when a human does it. With an LLM, the "trust me, I took extra care" is extremely doubtful. If LLMs could do that, they might as well use unsafe languages.
The whole point of the rust rewrite is that bun is now thought to rely on rust’s memory safety features, but that assumption doesn’t hold if everything’s inside an unsafe block.
Only ~4% of code is inside an unsafe block, so the idea is that for new code/contributions, the chance of introducing a new memory-safety bug is an order of magnitude lower.
Maybe in the future the unsafe code will go down to 1%, bringing that to two orders of magnitude.
Of course, only time will tell if that is true or not, but from experience I’d be willing to bet it is.
fn main() {
let mut x = 1_u32;
let reference_a = &mut x;
let reference_b = trust_me_bro(reference_a);
*reference_b = 2; -- Whoops
println!("reference_a: {reference_a} reference_b: {reference_b}");
}
After the call to trust_me_bro, two aliasing, mutable references exist simultaneously. This would usually be prevented by the borrow checker, but the unsafe code has effectively disabled it.
Not sure what you meant by this example since it doesn't compile. It seems the borrow checker caught your mischief. So much for effectively disabling stuff :P
You haven't effectively disabled anything; you just (tried to) wrote unsound code that washes one mutable ref as another. This stuff is allowed provided shared refs are never accessed at the same time (for example, panicking upon reading reference_b).
But you know what? If you're dabbling in unsafe, you have this big button called Tools in the playground. Choose Miri, then run your code; it will display large Undefined behavior. It even highlights the `trust_me_bro` function.
Hell, run this with UBSAN, ASAN, and other C tools. They will probably catch any such behavior.
If you know what I meant, then what's up with your snarky comment about "So much for effectively disabling stuff"? In your playground link, you did effectively disable the borrow checker in safe parts of the code. Next thing you're moving the goalpost, now it's not about external, static analysis tools: "run this with UBSAN, ASAN, and other C tools". I don't think you're arguing in good faith here. Goodbye.
Effectively means achieving the goal in satisfying manner.
Writing unsound code is less of effectively disabling borrow checker and more of a hack.
Think about it, if using Java unsafe I gain access to underlying HashMap array and do weird stuff to the HashMap invariants am I effectively turning HashMap into Array or am I doing a hack job?
Edit: By that logic since there is so much unsafe in the code base isn't borrow checker effectively already disabled? You can argue semantics but no, borrow checker isn't de facto or de jure invalidated by unsafe blocks.
It's invalidated by unsound unsafe and that's on code writer to fix.
Yeah but if you have tried writing unsafe Rust, you notice that you are obligating yourself to write code that is much stricter than C.
E.g. in C you can write code and say "don't call it outside the situation that this function was written for" and then blame [0] future users of the API.
In Rust you need to actually make sure that your code works, i.e. your safe interface is not unsafe.
[0] The blame game is not a technical solution to a technical problem...
Sure; but I bet raw pointers are used very infrequently in the new codebase. The code was ported from zig to rust. I bet a lot of pointers became rust references in the process.
You don't need to rehash the same old argument. Runtime memory management is forgiving but also inferior in a lot of ways to compiled stuff that works with memory deterministically.
Garbage collection is a method to make programming easier, not to make the resulting program better.
A garbage collected language does this automatically. Rust still requires thinking about and tracking memory lifecycles, but the borrow checker will complain and keep you from doing it wrong. That's why LLMs like Rust. It gives immediate feedback on what to fix. By-default constant reference parameters helps prevent major performance problems.