[Sytten]

This is really the crust of the argument. I absolutely love the Rust compiler for example, going back to Zig would feel a regression to me. There is a whole class of bugs that my brain now assumes the compiler will handle for me.

[pron]

Problem is, like they say the stock market has predicted nine of the last five recessions, the Rust compiler stops nine of every five memory safety issues. Put another way, while both Rust and Zig prevent memory safety issues, Zig does it with false negatives while Rust does it with false positives. This is by necessity when using the type system for that job, but it does come at a cost that disqualifies Rust for others...

Nobody knows whether Rust and/or Zig themselves are the future of low-level programming, but I think it's likely that the future of low-level programming is that programmers who prefer one approach would use a Rust-like language, while those who prefer the other approach would use a Zig-like language. It will be intesting to see whether the preferences are evenly split, though, or one of them has a clear majority support.

[tialaramex]

C++ already illustrates this idea you're talking about and we know exactly where this goes. Rust's false positives are annoying, so programmers are encouraged to further improve the borrowck and language features to reduce them. But the C++ or Zig false negatives just means your program malfunctions in unspecified ways and you may not even notice, so programmers are encouraged to introduce more and more such cases to the compiler.

The drift over time is predictable, compared to ten years ago Rust has fewer false positives, C++ has more false negatives.

You are correct to observe that there is no middle choice here, that's Rice's Theorem, non-trivial semantic correctness is Undecidable. But I would argue we already know what you're calling the "false positive" scenario is also not useful, we're just not at the point where people stop doing it anyway.

[pron]

> C++ already illustrates this idea you're talking about and we know exactly where this goes.

No, it doesn't. Zig is safer than C++ (and it's much simpler, which also has an effect on correctness).

Making up some binary distinction and then deciding that because C++ falls on the same side of it as Zig (except it doesn't, because Zig eliminates out-of-bounds access to the same degree as Rust, not C++) then what applies to one must apply to the other. There is simply no justification to make that equivalence.

> There is no middle choice here, that's Rice's Theorem, non-trivial semantic correctness is Undecidable.

That's nothing to do with Rice's theorem. Proving some properties with the type system isn't a general algorithm; it's a proof you have to work for in every program you write individually. There are languages (Idris, ATS) that allow you to prove any correctness property using the type system, with no false positives. It's a matter of the effort required, and there's nothing binary about that.

To get a sense of the theoretical effort (the practical effort is something to be measured empirically, over time) consider the set of all C programs and the effort it would take to rewrite an arbitrary selection of them in Rust (while maintaining similar performance and footprint characteristics). I believe the effort is larger than doing the same to translate a JS program to a Haskell program.

[tialaramex]

> There is simply no justification to make that equivalence.

I explained in some detail exactly why this equivalence exists. I actually have a small hope that this time there are enough people who think it's a bad idea that we don't have to watch this play out for decades before the realisation as we did with C and C++.

Yes it's exactly Rice's Theorem, it's that simple and that drastic. You can choose what to do when you're not sure, but you can't choose (no matter how much effort you imagine applying) to always be sure†, that Undecidability is what Henry Rice proved. The languages you mention choose to treat "not sure" the same as "nope", like Rust does, you apparently prefer languages like Zig or C++ which instead treat "not sure" as "it's fine". I have explained why that's a terrible idea already.

The underlying fault, which is why I'm confident this reproduces, is in humans. To err is human. We are going to make mistakes and under the Rust model we will curse, perhaps blame the compiler, or the machine, and fix our mistake. In C++ or Zig our mistake compiles just fine and now the software is worse.

† For general purpose languages. One clever trick here is that you can just not be a general purpose language. Trivial semantic properties are easily decided, so if your language can make the desired properties trivial then there's no checking and Rice's Theorem doesn't apply. The easy example is, if my language has no looping type features, no recursive calls, nothing like that, all its programs trivially halt - a property we obviously can't decidably check in a general purpose language.

[pron]

> I explained in some detail exactly why this equivalence exists.

No, you assumed that Zig and C++ are equivalent and concluded that they'll follow a similar trajectory. It's your premise that's unjustified.

A problem you'd have to contend with is that Rust is much more similar to C++ than Zig in multiple respects, which may matter more or less than the level of safety when predicting the language trajectory.

> But you can't choose (no matter how much effort you imagine applying) to always be sure

That is not Rice's theorem. You can certainly choose to prove every program correct. What you cannot do is have a general mechanism that would prove all programs in a certain language correct.

> One clever trick here is that you can just not be a general purpose language.

That's not so much a clever trick as the core of all simple (i.e. non-dependent) type systems. Type-safety in those languages then trivially implies some property, which is an inductive invariant (or composable invariant) that's stronger than some desired property. E.g. in Rust, "borrow/lifetime-safety" is stronger than UAF-safety.

However, because an effort to prove any property must exist, we can find it for some language that trivially offers it by looking at the cost of translating a correct program in some other language that doesn't guarantee the property to one that does. The reason why it's more of a theoretical point than a practical one is because it could be reasonably argued that writing a memory-safety program in C is harder than doing it in Rust in the first place, but either way, there's some effort there that isn't there when writing the program in, say, Java.

[akkad33]

> No, you assumed that Zig and C++ are equivalent and concluded that they'll follow a similar trajectory. It's your premise that's unjustified.

They did not say Zig and C++ are equivalent

[uecker]

And yet, in reality, Rust is also on the "if I am not sure I simply attest that it is fine" side on the fence.

[tialaramex]

I've been hearing about how I'll inevitably write all this unsafe Rust for... four years now.

Some time back I checked and I had written exactly one unsafe block, and so I inspected it again and I realised two things:

1. It was no longer necessary, Rust could now just do this safely. I rewrote it in safe Rust.

2. It was technically Undefined Behaviour, predictably given the chance to shoot myself in the foot that's exactly what I had done. Like a lot of C and C++ it likely wouldn't in fact blow my foot off in any real scenario, but who knows? Not me, that's for sure.

[ViewTrick1002]

Which is why there is an effort to formally verify the unsafe use in the Rust standard library.

I would also say that unsafe causes a very different human reaction.

When like Zig, C or C++ everything is potentially unsafe then you can't scrutinize everything.

When submitting a PR in Rust containing unsafe code everyone wants to understand what happens because it is both rare, and everyone are cautious about the dangers posed. The first question on everyone's mind always is: Does this need unsafe?

[surajrmal]

What is your reason to claim zig is safer than c++?

[messe]

Bounds safety by default, nullability is opt-in and checks are enforced by the type-system, far less "undefined behaviour", less implicit integer casting (the ergonomics could still use some work here), etc.

This is on top of the cultural part, which has led to idiomatic Zig being less likely to heap allocate in the first place, and more likely to consider ownership in advance. This part shouldn't be underestimated.

[tialaramex]

> This part can't be underestimated.

You presumably intend "shouldn't be underestimated" rather than "can't be". I agree that culture is crucial, but the technology needs to support that culture and in this respect Zig's technology is lacking. I would love to imagine that the culture drives technology such that Zig will fix the problem before 1.0, but Zig is very much an auteur language like Jai or Odin, Andrew decides and he does not seem to have quite the same outlook so I do not expect that.

[CyberDildonics]

> Zig is safer than C++

Maybe if someone bends over backwards to rationalize it, but not in any real sense. Zig doesn't have automatic memory management or move semantics.

In C++ you can put bounds checking in your data structures and it is already in the standard data structures. You can't build RAII and moves into zig.

[pron]

> Maybe if someone bends over backwards to rationalize it, but not in any real sense.

In a simple, real sense. Zig prevents out-of-bounds access just as Rust does; C++ doesn't. Interestingly, almost all of Rust's complexity is invested in the less dangerous kind of memory unsafety (https://cwe.mitre.org/top25/archive/2024/2024_cwe_top25.html).

> You can't build RAII and moves into zig.

So RAII is part of the definition of memory safety now?

Why not just declare memory safety to be "whatever Rust does", say that anything that isn't exactly that is worthless, and be done with that, since that's the level of the arguments anyway.

We could, of course, argue over which of Rust, Zig, and C++ offers the best contribution to correctness beyond the sound guarantees they make, except these are empirical arguments with little empirical data to make any determination, which is part of my point.

Software correctness is such a complicated topic and, if anything, it's become more, not less, mysterious over the decades (see Tony Hoare's astonishment that unsound methods have proven more effective than sound methods in many regards). It's now understood to be a complicated game of confidence vs cost that depends on a great many factors. Those who claim to have definitive solutions don't know what they're talking about (or are making unfounded extrapolations).

[CyberDildonics]

C++ doesn't.

Then why do my data structures detect if I go out of bounds?

Interestingly, almost all of Rust's complexity is invested in the less dangerous kind of memory unsafety

I didn't say anything about rust.

So RAII is part of the definition of memory safety now?

Yes. You can clean up memory allocations automatically with destructors and have value semantics for memory that is on the heap.

Why not just declare memory safety to be "whatever Rust does", say that anything that isn't exactly that is worthless, and be done with that, since that's the level of the arguments anyway.

Why are you talking about rust here? Focus on what I'm saying.

We could, of course, argue over which of Rust, Zig, and C++

if anything, it's become more, not less, mysterious over the decades

Says who?

I don't care about rust or zig, I'm saying that these are solved problems in C++ and I don't have to deal with them. Zig does not have destructors and move semantics.

[rowanG077]

Unless you actually use the simplicity to apply formal methods I don't think simplicity make a language safer. The exact opposite. You can see it play out in the C vs C++ arena. C++ is essentially just a more complex C. But I trust modern C++ much more in terms of memory safety.

[pron]

> Unless you actually use the simplicity to apply formal methods I don't think simplicity make a language safer.

That depends what you mean by "safer", but it is an empirical fact that unsound methods (like tests and code reviews) are extremely effective at preventing bugs, so the claim that formal methods are the only way is just wrong (and I say this as a formal methods guy, although formal methods have come a long way since the seventies, when we thought the point was to prove programs correct).

> The exact opposite. You can see it play out in the C vs C++ arena. C++ is essentially just a more complex C. But I trust modern C++ much more in terms of memory safety.

I don't understand the logical implication. From the fact that there exists a complicating extension of a language that's safer in some practical way than the original you conclude that complexity always offers correctness benefits? This just doesn't follow logically, and you can immediately see it's false because Zig is both simpler and safer than C++ (and it's safer than C++ even if its simplicity had no correctness benefits at all).

[rowanG077]

> That depends what you mean by "safer", but it is an empirical fact that unsound methods (like tests and code reviews) are extremely effective at preventing bugs, so the claim that formal methods are the only way is just wrong (and I say this as a formal methods person)

I agree that tests and reviews are somewhat effective. That's not the point. The point is that if you look at the history of programming languages simplicity in general goes against safety. Simplicity also goes against human understanding of code. C and assembly are extremely simple compared to java, python, C#, typescript etc. yet programs written in C and assembly are much harder to understand for humans. This isn't just a PL thing either. Simplicity is not the same as easy, it often is the opposite.

> I don't understand the logical implication. From the fact that there exists a complicating extension of a language that's safer in some practical way than the original you conclude that complexity always offers correctness benefits? This just doesn't follow logically, and you can immediately see it's false because Zig is both simpler and safer than C++ (and it's safer than C++ even if its simplicity had no correctness benefits at al

It's the greatest example of you take a simple language, you add a ton of complexity and it becomes more safe. You are right that zig is simpler and safer, but it's a green field language. Else I might as well say rust is more safe than zig and also more complex. The point is as to isolate simplicity as the factor as much as possible.

I would even say that zig willingly sacrifices safety on the alter of simplicity.

[Sytten]

So far I think the adoption in critical infrastructure (Linux, AWS, Windows, etc.) is clearly in Rust favor but I agree that something at some point will replace Rust. My belief is that more guardrails will end up winning no matter the language since the last 50 years of progamming have shown us we can't rely on humans to write bug free code and it is even worse with LLM.

[conorbergin]

I think the problem with this attitude is the compiler becomes a middle manager you have to appease rather than a collaborator. Certainly there are advantages to having a manager, but if you go off the beaten track with Rust, you will not have a good time. I write most of my code in Zig these days and I think being able to segfault is a small price to pay to never have to see `Arc<RefCell<Foo<Bar<Whatever>>>` again.

[Sytten]

I view it as a wonderful collaborator, it tells me automatically were my code is wrong and it gets better with every release, I can't complain really. I think a segfault is a big price to pay, but it depends on the criticality of it I guess.

[pron]

Not to mention that `Arc` uses a GC (and not a stellar one, at that)...

[surajrmal]

You can use alternative GC such as crossbeam if you want. You're not locked into using an Arc.

[veber-alex]

Lol, what are you even trying to say here?

Is Zig such an amazing language that while using it you won't ever need reference-counted pointers?

[the__alchemist]

You can write rust without over-using traits. Regrettably, many rust libs and domains encourage patterns like that. One of the two biggest drawbacks of the rust ecosystem.

[surajrmal]

I can't imagine writing c++ or c these days without static analysis or the various llvm sanitizers. I would think the same applies to zig. Rather than need these additional tools, rust gives you most of their benefits in the compiler. Being able to write bugs and have the code run isn't really something to boast about.

[conorbergin]

I would rather rely on a bunch of sanitizers and static analysis because it is more representative of the core problem I am solving: Producing machine code. If I want Rust to solve these problems for me I now have to write code in the Rust model, which is a layer of indirection that I have found more trouble than it's worth.

[ViewTrick1002]

How do you guard concurrent access in your multithreaded code?

Due diligence every single time after the tenth refactor?

[Zambyte]

In practice, almost all memory safety related bugs caught by the Rust compiler are caught by the Zig safe build modes at run time. This is strictly worse in isolation, but when you factor in the fact that the rest of the language is much easier to reason about, the better C interop, the simple yet powerful metaprogramming, and the great built in testing tools, the tradeoffs start to become a lot more interesting.

[dnautics]

catching at compile time is much better, though. there are plenty of strange situations that can happen that you'll not reach in runtime (for example, odds of running into a tripwire increase over time, things that can only happen after certain amount of memory fragmentation -- maybe you forgot an errdefer somewhere, etc.)

[munchler]

Nit: I think you want crux in that phrase, not crust.

[Sytten]

Thanks! Cant edit anymore, I guess I was feeling hungry this morning

[dnautics]

would you be satisfied if there was a static safety checker? (or if it were a compiler plugin that you trigger by running a slightly different command?). Note that zig compiles as a single object, so if you import a library and the library author does not do safety checking, your program would still do the safety checking if it doesn't cross a C abi boundary.

https://www.youtube.com/watch?v=ZY_Z-aGbYm8