by NobodyNada | 2025-11-10 23:56:22+00:00
> it's just silly to draw a a particular sharp line between Rust and Zig because they perform exactly the same (in terms of sound guarantees; we're ignoring any softer effects) for most top weaknesses.

There is a very clear sharp line between them in that Rust has no undefined behavior outside of an unsafe block. This matters because the effects of undefined behavior -- particularly memory-corrupting undefined behavior -- are unbounded. Security issues caused by logic bugs are limited to only having local effects on the program -- a SQL injection bug can lead to the wrong SQL query being executed, a path traversal bug can lead to the wrong path being accessed, and a shell escaping bug can lead to execution of the wrong shell command. These are severe problems that can lead to data exfiltration or remote code execution, but the relationship between bug and effect is straightforward: "I'm passing user input to a shell here; this could have catastrophic consequences so I'd better review this carefully." In contrast, undefined behavior can happen anywhere in your program, and it can do anything. That is a clear and measurable difference, and emperical evidence from the last 10 years clearly indicates both that it is nigh impossible to write large C/C++ applications without both spatial and temporal memory safety vulnerabilities, and that adopting Rust measurably decreases the incidence of such vulnerabilities.

Zig is certainly an improvement over C on this front, but it is still a UB-heavy language, and that's where the sharp line is. It's hard to make emperical comparisons because Zig is so young, but the comparision between Deno and Bun in the article is a reasonably strong demonstration that Zig has not achieved a comparable level of memory safety to Rust.

> Sure, but then you might as well also consider softer effects. For example, maybe a language that's easier to review because it's more explicit, or a language that's faster to compile and is easier to test wins.

> And I agree that we should consider all these, but then we start seeing why correctness is such a complicated topic, and we could speculate just as easily that it is Zig that "clearly" wins.

This doesn't really have anything to do with my point that the CVE list does not provide evidence to dismiss temporal memory safety as irrelevant; it's more of a general statement on writing correct software. But regardless, "Zig has nullability and bounds checks" and "Rust has an affine type system, statically-checked immutability and exclusivity, language-level resource management, and no undefined behavior" are not in the same league of program correctness. Rust wasn't designed after some ideal of memory safety at the expense of clarity and correctness: the lifetime and type system came from a goal of reducing logic bugs in complex concurrent programs, and the fact that it is powerful enough to achieve memory safety without garbage collection was a happy accident. The emperical results that Rust programs have fewer memory-safety vulnerabilities demonstrate that Rust's static approach to software correctness is successful, and not just for the specific problem of memory safety, because Rust's tooling for achieving program correctness is generalizable to arbitrary application invariants. This lines up with my own experience; software I write using Rust is far easier to get right, more reliable, and easier to successfully maintain and refactor than anything else I've done.

Certainly Zig has its strong points as well -- explicitness can reduce complexity and compile times, but it also has downsides of pushing complexity into application code (thus making it harder to review and introducing more opportunities to create mistakes). A proper comparison of the two approaches is worthwhile, but just as "Rust is more memory safe" is an overly reductive generalization of the langauges' approach to software correctness, "there's a rather small difference between Rust and Zig" simply isn't true.