[bit1993]

> ... then we can make C safe without any technical changes just by adding some language to the standard saying that C programmers are obliged to ensure that their code maintains a certain list of invariants.

In Rust you can use #![forbid(unsafe_code)] to totally forbid unsafe code in your codebase. Rust also checks for memory safety at compile time, these are strong guarantees that ensure that if the code compiles it is memory safe.

[foldr]

I'm aware of that, but I'm responding to the original claim that "Rust makes the same guarantees regardless of the unsafe keyword" (see https://news.ycombinator.com/item?id=46262774)

[bit1993]

Ah. I agree with you. When unsafe is used the borrow checker cannot check for memory safety, the programmer has to provide the guarantees by making sure their code does not violate memory safety, similar to programming in C.

But unsafe Rust is still far better than C because the unsafe keyword is visible and one can grep it and audit the unsafe parts. Idiomatic Rust also requires that the programmer provides comments as to why that part is unsafe.