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Comment by banachtarski | Hacker News Reader

> This is why if you're currently writing C or C++, please, please look into Rust.

Ugh if you read the article, you would know that the UB described here is the same in Rust. There is this massive group think about which languages are safe and/or fast, and whenever an article like this comes up, invariably someone says "Rust!" without really looking at the problem itself.

Personally, I am in wait and see mode on Rust. Without better generics support (aka template <size_t> or similar) and a number of other things, it still doesn't meet my bar for writing fast generic code, and who knows how complex it will be at that point? I say the jury is still out.

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> Ugh if you read the article, you would know that the UB described here is the same in Rust.

Rust doesn't have a formal memory model yet, but it's already known that UB in Rust is quite restricted:

https://doc.rust-lang.org/nomicon/what-unsafe-does.html

Most importantly, UB in Rust should only arise if you're writing unsafe code (barring compiler bugs). Typically, most Rust code is safe. This is a huge win.

> Ugh if you read the article, you would know that the UB described here is the same in Rust. There is this massive group think about which languages are safe and/or fast, and whenever an article like this comes up, invariably someone says "Rust!" without really looking at the problem itself.

Rust does have vocal proponents, but I don't see how "the UB described here is the same in Rust". Rust should trap consistently when dividing by zero.

> the UB described here is the same in Rust

I don't think this is correct. Dividing by zero in Rust produces a panic, and panics are observable side effects that may not be reordered with other side effects. This is sometimes annoying, because it can prevent the compiler from eliminating bounds checks in some cases, but it avoids the problems mentioned in this article.

> Ugh if you read the article, you would know that the UB described here is the same in Rust.

Ugh, if you took the time to learn Rust before criticizing it, you'd know that Rust only allows undefined behavior in unsafe blocks.

> Without better generics support

So you have no idea what generics are. Templates aren't generics, they're fancy code generators expanded at compile time, which means they're incredibly loosely typed and allow you to do things like have scalar parameters like size_t n (because they're basically macros). C++ templates are essentially a form of duck typing that has led to an increased need for specification, hence concepts in C++20.

Rust's parametric polymorphism and type classes (aka generics) follows in the ML and Haskell tradition in that the type checking is like a constraint program that is run at compile time. When a generic item is invoked, the specification of that type is immediately checked for consistency at the call site, otherwise the typechecking fails.

UB is a way to better optimize code by (silently) offloading a burden of correctness proof to a programmer. Rust prefers to be more explicit about it. Const generics will surely not change that.

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