[chancancode]

Have you read "Learning Rust With Entirely Too Many Linked Lists"[1]? I think it will be quite helpful for these kind of situations. It walks you through all the possible tools in the language that is available to you, and at the end, if you just want to write it how you would in C, you could always do it "unsafely" with raw pointers (which is no worse than C).

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[1] http://cglab.ca/~abeinges/blah/too-many-lists/book/

[alphaalpha101]

It's also really no better than C. Or at least no better than C++.

This is my main issue with Rust. It doesn't seem to really solve the right problem. I feel like it solves the easy problems that I already know how to solve easily, but as soon as I get to something that really, truly feels like I want it, the best solution is unsafe.

A complicated circular linked data structure is exactly where I want the language to be screaming at me if I make a silly error. But Rust doesn't even consider memory leaks to be errors...

[AsyncAwait]

I don't know, ensuring memory safety at compile time and safe concurrency is a pretty big win for me over C, I know many people who claim that they can write/debug C programs to be memory safe, however the real world would respectfully disagree.

[alphaalpha101]

Rust doesn't ensure memory safety or safe concurrency. It ensures memory safety - including data race safety, just one part of safe concurrency - assuming you never use any unsafe code and that the standard library is free of bugs. I'm happy to assume the standard library is free of memory safety bugs, because you have to trust something.

But I'm not happy trusting that dependencies aren't using unsafe code, and I'm not happy claiming that Rust ensures safety, when it ensures safety only if you assume that unsafe blocks aren't unsafe.

The problem is that you can't check unsafe blocks locally. Checking that each individual unsafe block doesn't have undefined behaviour requires checking the entire programme.

It's better than nothing, without a doubt, but it isn't safe.

[oconnor663]

Unsafe blocks are infectious, that's true, but it's possible to write safe APIs that limit that infectiousness to a single module. For example, even though Vec's implementation is crazy unsafe, you don't have to audit all the uses of Vec in safe programs -- a local audit of the Vec code can prove what we need to prove. This is the biggest benefit of the lifetime system and the borrow checker, that when we write piles of unsafe code, we can force safe callers to maintain our invariants.

[alphaalpha101]

You can prove it, but you can also prove that a C++ programme has no memory safety bugs. And there are a lot of languages where you don't have to, where it's simply impossible to get memory safety bugs (assuming the runtime is safe).

For nontrivial libraries that use a lot of unsafe, it really is very difficult to know that all the uses of unsafe don't interact in some way to create unsafety. The scoped lock that had a problem in Rust 1.0 (or just before it?) is an example.

You can force callers to maintain your invariants in C++ too, simply by using some basic safety. Yes people can still do things that are obviously visually unsafe in code and undefined, but that's not a serious issue.

I still think Rust is better here. Don't get me wrong. But it's very hyped as 'safe and fast' when it just isn't safe.

[sitkack]

If freedom from data and race conditions is the easily solved problems, I'll take it.

The problems with engineering solutions that approach something close to the end of the spectrum of perfection, is that it gets undo criticism for not being perfect-enough. Rust is hopefully a stepping stone along path towards more correct, less error prone computation. Lets not throw the baby out with the bathwater.

[jacobush]

Here have an upvote. Can someone else comment/refute this?

[kevincox]

I don't really have a refutal, but more of a dismissal.

Almost all of the code I write just uses prebuilt data structures (other then structs to group things) and when writing this code I find the safety measures that rust provides very convenient because I don't have to worry about these things such as lifetimes. It is nice knowing that the compiler will let me know if I make an error.

However yes, it doesn't solve the hard probem of complex circular structures. I don't see this as a major issue because when I am writing these I am carefully thinking about the strucutre anyways. So yes, while it would be nice to have these verified as well I wouldn't want take the tradeoff if it made the language much more complex.

[gcp]

Most of us write new, complex data-structures, that aren't part of the stdlib or a crate, like once a year, at most. Those are hard in Rust if they involve circular pointers. They're hard in C/C++ too, but in a different way (easier to write the code, harder to be sure it's correct).

The idea that Rust would be no better than C/C++ because of the latter parts doesn't make much sense. This kind of work is unusual for most programming. To say that other programming work is easy does not seem to bear out in practice.

And as has been becoming clear in this thread, if you're inventing new data structures, the odds are you overlooked an already existing better alternative.

[alphaalpha101]

It doesn't matter that it's 'kind of unusual', even though I contend that it isn't. Even if, for the sake of argument, we assume that it is, that doesn't change my point.

My point is that the whole point of Rust is supposedly that it

>is a systems programming language that runs blazingly fast, prevents segfaults, and guarantees thread safety.

except that when you look at any of the examples of code that really would benefit from the compiler's help, the compiler just throws its hands in the air and goes 'it's all up to you now'.

The problem is that Rust doesn't let you make a single assumption and let the compiler prove the safety of the code using that assumption. It just has a valve that you can hit that removes all guarantees.

If you could say 'this code is safe assuming that this FFI function doesn't exhibit undefined behaviour, please check that for me' or write a proof that says 'this actually is safe, because this pointer can only ever point into this valid memory or this valid memory, and this is why' then the compiler would still be useful.

Whether 'this work' (which is not just creating data structures, but anything that the compiler doesn't understand, which is much broader than just creating data structures) is unusual or not, IMO the whole appeal of Rust is that it makes doing that work easy. But it doesn't.

Rust just doesn't seem worth it, doesn't seem worth rewriting whole ecosystems of code. It doesn't give any actual safety.

[Rusky]

> examples of code that really would benefit from the compiler's help

This seems to be the point of disagreement here, and I think evidence clearly shows that you are wrong. Sure, Rust doesn't help you when writing the implementation of e.g. circular data structures. But what it does do is provide, far beyond C or C++, the tools for the author of that data structure to enforce that it's used correctly.

And as mentioned upthread, most memory/concurrency (especially concurrency) bugs are not in the implementations of these structures, but in their use. So Rust is a fantastic win here, empirically speaking. Look at the rate of memory safety bugs in Rust programs vs C++ programs- Ripgrep vs grep, Servo/Quantum vs Firefox, etc.

[staticassertion]

Sure...

* Most developers are not writing data structures, so optimizing for that seems unnecessary.

* There is work and research going into verifying unsafe code

* I think historically we can see that most memory safety vulnerabilities are not going to be in some lower level data structure, which is well encapsulated and likely already built by someone else, but in the use of that data structure. In particular - sharing references and also invalidating data safely without leaving references to that data. Rust helps you here, and this seems like the far better target.

* Even if your rust code uses unsafe, you still have benefits - you know where to audit for unsafety, you know where to pay extra close attention, and you can still write a large portion of your code in safe rust.

[andrewflnr]

AFAIK, verifying complex linked data structures is still an active research topic. For instance: https://cs.au.dk/~amoeller/papers/pale/pale.pdf

Edit: or try something like Idris. But I think you're asking too much of today's rustc.

[reificator]

Beat me to this by six hours. Can vouch that the above link is quite helpful when learning Rust.