NaN != NaN

If you’re using a decent development system, you’ll have an executable called diff installed already :)

Replace Sunshine with Super Mario Eclipse. It has the original shine sprites, huge quality of life improvements, and an insane amount of new content.

That’s not the point, though. The point is to use a nominal type that asserts an invariant and make it impossible to create an instance of said type which violates the invariant.

Both validation functions and refinement types put the onus on the caller to ensure they’re not passing invalid data around, but only refinement types can guarantee it. Humans are fallible, and it’s easy to accidentally forget to put a check_if_valid() function somewhere or assume that some function earlier in the call stack did it for you.

With smart constructors and refinement types, the developer literally can’t pass an unvalidated type downstream by accident.

You’re going to need to cite that.

I’m not familiar with C23 or many of the compiler-specific extensions, but in all the previous versions I worked with, there is no type visibility other than “fully exposed” or opaque and dangerous (void*).

You could try wrapping your Foo in

typedef struct {
    Foo validated
} ValidFoo;

But nothing stops someone from being an idiot about it and constructing it by hand:

ValidFoo trustMeBro;
trustMeBro.validated = someFoo;
otherFunction(trustMeBro);

Or even just casting it.

Foo* someFoo;
otherFunction((ValidFoo*) someFoo);

If it were poorly designed and used exceptions, yes. The correct way to design smart constructors is to not actually use a constructor directly but instead use a static method that forces the caller to handle both cases (or explicitly ignore the failure case). The static method would have a return type that either indicates “success and here’s the refined type” or “error and this is why.”

In Rust terminology, that would be a Result<T, Error>.

For Go, it would be (*RefinedType, error) (where dereferencing the first value without checking it would be at your own peril).

C++ would look similar to Rust, but it doesn’t come as part of the standard library last I checked.

C doesn’t have the language-level features to be able to do this. You can’t make a refined type that’s accessible as a type while also making it impossible to construct arbitrarily.

Unless you’re a functional programming purist or coming from a systems programming background, it takes a lot longer than a few days to get used to the borrow checker. If you’re coming as someone who most often uses garbage-collected languages, it’s even worse.

The problem isn’t so much understanding what the compiler is bitching about, as it is understanding why the paradigm you used isn’t safe and learning how to structure your code differently. That part takes the longest and only really starts to become easier when you learn to stop fighting the language.

Of course. Rust isn’t immune to logic errors, off-by-one mistakes, and other such issues. Nor is it memory safe in unsafe blocks.

Just by virtue of how memory safety issues account for 50%+ of vulnerabilities, it’s worth genuinely considering as long as the bindings don’t cause maintainability issues.

Let me know when you find one?

The first directory block is a hole. But type == DIRENT, so no error is reported. After that, we get a directory block without ‘.’ and ‘…’ but with a valid dentry. This may cause some code that relies on dot or dotdot (such as make_indexed_dir()) to crash

The problem isn’t that the block is a hole. It’s that the downstream function expects the directory block to contain . and .., and it gets given one without because of incorrect error handling.

You can encode the invariant of “has dot and dot dot” using a refinement type and smart constructor. The refined type would be a directory block with a guarantee it meets that invariant, and an instance of it could only be created through a function that validates the invariant. If the invariant is met, you get the refined type. If it isn’t, you only get an error.

This doesn’t work in C, but in languages with stricter type systems, refinement types are a huge advantage.

Arrogant hypocrites are a pet peeve of mine. If someone is going to act like progressive technology changes are beneath them and unnecessary, they should be able to put their money where their mouth is.

Wait, yeah. I was thinking of ad hominem when i wrote that, sorry. Correct, that is a strawman.

I understand his experience is hard to match, we all have something in our lives we’re that good at

At some point, that mix of experience and ego becomes a significant liability. He’s directly hurting the adoption of Rust in the kernel, while the C code he’s responsible for is full of problems that would have been impossible if written in safe Rust.

CVE-2024-42304 — crash from undocumented function parameter invariants
CVE-2024-40955 — out of bounds read
CVE-2024-0775 — use-after-free
CVE-2023-2513 — use-after-free
CVE-2023-1252 — use-after-free
CVE-2022-1184 — use-after-free
CVE-2020-14314 — out of bounds read
CVE-2019-19447 — use-after-free
CVE-2018-10879 — use-after-free
CVE-2018-10878 — out of bounds write
CVE-2018-10881 — out of bounds read
CVE-2015-8324 — null pointer dereference
CVE-2014-8086 — race condition
CVE-2011-2493 — call function pointer in uninitialized struct
CVE-2009-0748 — null pointer dereference

There’s really only one valid response to Ted Ts’o:

If you think you can do better with C, prove it.

CVE-2024-42304 — crash from undocumented function parameter invariants
CVE-2024-40955 — out of bounds read
CVE-2024-0775 — use-after-free
CVE-2023-2513 — use-after-free
CVE-2023-1252 — use-after-free
CVE-2022-1184 — use-after-free
CVE-2020-14314 — out of bounds read
CVE-2019-19447 — use-after-free
CVE-2018-10879 — use-after-free
CVE-2018-10878 — out of bounds write
CVE-2018-10881 — out of bounds read
CVE-2015-8324 — null pointer dereference
CVE-2014-8086 — race condition
CVE-2011-2493 — call function pointer in uninitialized struct
CVE-2009-0748 — null pointer dereference

Part of the hostility was the other maintainer misunderstanding the presenter, going on a diatribe about how the kernel Rust maintainers are going to force the C code to become unrefactorable and stagnate, and rudely interrupting the presenter with another tangent whenever he (the presenter) tried to clarify anything.

An unpleasant mix of DM railroading and gish galloping, essentially.

I wouldn’t quite call it a strawman, but the guy was clearly not engaging in good faith. He made up hypothetical scenarios that nobody asked about, and then denigrated Rust by attacking the scenarios he came up with.

Edit: I was thinking of the wrong fallacy. It is a strawman, yes.

The “P” stands for “Private”

Recursion makes it cheaper to run in the dev’s mind, but more expensive to run on the computer.

Maybe for a Haskell programmer, divide-and-conquer algorithms, or walking trees. But for everything else, I’m skeptical of it being easier to understand than a stack data structure and a loop.

In a single one-off program or something that’s already fast enough to not take more than a few seconds—yeah, the time is spent better elsewhere.

I did mention for a compiler, specifically, though. They’re CPU bottlenecked with a huge number of people or CI build agents waiting for it to run, which makes it a good candidate for squeezing extra performance out in places where it doesn’t impact maintainability. 0.02% here, 0.15% there, etc etc, and even a 1% total improvement is still a couple extra seconds of not sitting around and waiting per Jenkins build.

Also keep in mind that adding features or making large changes to a compiler is likely bottlenecked by bureaucracy and committee, so there’s not much else to do.

Not necessarily. It depends on what you’re optimizing, the impact of the optimizations, the code complexity tradeoffs, and what your goal is.

Optimizing many tiny pieces of a compiler by 0.02% each? It adds up.

Optimizing a function called in an O(n²) algorithm by 0.02%? That will be a lot more beneficial than optimizing a function called only once.

Optimizing some high-level function by dropping into hand-written assembly? No. Just no.

Yeah, you have to be pretty deranged to mix multithreading and recursion together.