[milesrout]

You might think so. I strongly disagree. I think Rust's supposed memory safety advantages are a distraction. If people really cared about that above all else they would use a memory-safe language, which Rust is not, such as Java or Python or Haskell or something. There are tons.

Governments aren't "bugging" anyone about memory safety and if they were, they wouldn't want you to use Rust. Rust isn't memory-safe.

[kobebrookskC3]

> If people really cared about that above all else they would use a memory-safe language, which Rust is not, such as Java or Python or Haskell or something.

people already use languages like java or python or js in most cases! it's only in rare cases it made sense to write stuff in c or c++. now with rust, that niche becomes even smaller.

> Governments aren't "bugging" anyone about memory safety

idk this report sounds like bugging from governments (plural) to me: https://www.cisa.gov/sites/default/files/2023-12/The-Case-fo...

no one who isn't being obtuse would say rust isn't memory safe. the linked report also deems rust a memory safe language.

[oneshtein]

Safe Rust is memory-safe enough for practical needs, while maintaining top performance.

[menaerus]

Is it still safe even if it depends on the dependencies which are not safe?

[whytevuhuni]

Note that memory-safe languages like Java and Python will also depend on libraries which are not safe, e.g. in their implementation of the interpreter/VM, standard library, native libraries like numpy, etc.

In practice unsafe Rust tends to be less than 1% of the code (or around 5% in low-level things like kernels), which is a similar ratio of trusted/untrusted code. The top-level application code is generally expected to have 0%.

[milesrout]

This statistic is based on the lines of code bounded by the "unsafe" keyword but that is not the full picture. Unsafe code relies for its safety on the logical correctness of safe code. In theory, as "proper practice", the trust boundary should be the crate. In other words, the safety of a particular "unsafe" block should be verifiable by checking the correctness of code within the same crate. In practice, this is not true: much unsafe code relies for safety on correctness properties in external code, especially from the standard library, like the fact that "Vec" stores elements contiguously in memory in order of index.

That isn't to say the concept is useless. But it is not the case that you just need to inspect code marked "unsafe". A change to code not marked "unsafe" can break the invariants and assumptions that unsafe blocks elsewhere rely on.

[damon_dam]

Agreed. I would add to your argument as follows.

If you stick with "21st Century C++" [1], you never have to use a pointer. At some point, there will be (say) a -W20 flag that produces a warning if you use a pointer or other potentially-unsafe idiom without marking it with a [[20th_century]] attribute.

That attribute is equivalent to Rust's unsafe keyword. At that point, the safety difference will boil down to opt-in versus opt-out. But you can already opt-in today by policing yourself.

That's quite far from the radical language difference it's made out to be.

[1] https://news.ycombinator.com/item?id=42946321

[whytevuhuni]

I've used both, and I'd say it's still quite a difference.

There's many examples, but one I stumble on often is functions that accept a std::string_view, and return a part of that string. It's quite dangerous to make it return a std::string_view as well, especially given how easy it is to create temporaries (e.g. get_word(sentence1 + sentence2) would return a string_view to temporary data). Similar story with functions that return element references out of collections, functions that choose an element out of two, etc.

In Rust on the other hand, you can get very reckless with very long chains of functions that return references out of other references, especially with parsers, iterators, and lambdas/closures.

The Send/Sync traits for thread safety are also unmatched in C++, tagged union pattern matching will also heavily restrict invalid states, and so will Rust's affine(ish) types, which force a single owner for resources, as opposed to C++'s somewhat hard-to-use move semantics.

The standard library also prefers safety over speed by default, e.g. with std::string_view's indexing being UB, std::optional's dereference being UB, and so on.

[whytevuhuni]

That's right, unsafety extends to the whole module, and anything else that relies on the module's internal implementation. Generally all the way up to the abstraction's public API, whatever that abstraction is (a Vec, a Mutex, etc).

But it's nevertheless still not different from other languages that are deemed memory safe.

[kobebrookskC3]

modules are meant to be the boundary for a safe abstraction, but sometimes you get fun holes like https://github.com/rust-lang/rust/issues/128872 where you can implement Copy for a type in a different module in the same crate, even if the fields are private

[kobebrookskC3]

seems pretty safe in practice https://security.googleblog.com/2024/09/eliminating-memory-s...

[menaerus]

I know it's an unpopular opinion but tbh those Google security blogs always read more as a marketing material than engineering effort. Why I think so it's because statistics always has two side of the coins - if you want to make something look better or worse than it really is, it's trivial to do so. There's simply not enough data or methodology or different angles taken for me personally to take these blogs as a very relevant source of information but YMMV. We are all different.

[oneshtein]

Any and all safe code depends on unsafe code to do something, including Java and Python. Yep, unsafe code may contains bugs, but their surface is much smaller, so, at same ratio of bugs to code, numbers of bugs is much smaller.

[menaerus]

If you're open to a bit different and perhaps thought provoking perspective let me say that for your hypothesis to be true we would need to assume that the distribution of memory-safety bugs is uniform across the codebase. From my experience this is not true, it usually follows uni-modal or at most bi-modal distribution, so it follows that the surface is not much smaller.