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0 pointsselfmodruntime1y ago0 comments

This is not really true. You have to uphold those guarantees yourself. With unsafe preconditions, if you don't, the code will still crash loudly (which is better than undefined behaviour).

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littlestymaar1y ago

With unsafe you get exactly the same kind of semantics as C, if you don't uphold the invariant the unsafe functions expect, you end up with UB exactly like in C.

If you want a clean crash instead on indeterministic behavior, you need to use assert like in C, but it won't save you from compiler optimization removing checks that are deemed useless (again, exactly like in C).

lenkite1y ago

> With unsafe you get exactly the same kind of semantics as C

People seem to disagree.

Unsafe Rust Is Harder Than C

https://chadaustin.me/2024/10/intrusive-linked-list-in-rust/

https://news.ycombinator.com/item?id=41944121

kibwen1y ago

Using references in unsafe Rust is harder than using raw pointers in C.

Using raw pointers in unsafe Rust is easier than using raw pointers in C.

The solution is to not manipulate references in unsafe code. The problem is that in old versions of Rust this was tricky. Modern versions of Rust have addressed this by adding first-class facilities for producing pointers without needing temporary references: https://blog.rust-lang.org/2024/10/17/Rust-1.82.0.html#nativ...

selfmodruntimeOP1y ago

> With unsafe you get exactly the same kind of semantics as C, if you don't uphold the invariant the unsafe functions expect, you end up with UB exactly like in C.

This is not exactly true. Even in production code, unsafe preconditions check if you violate these rules.

Here: https://doc.rust-lang.org/core/macro.assert_unsafe_precondit... And here: https://google.github.io/comprehensive-rust/unsafe-rust/unsa...

bangaladore1y ago

Quoted from your link

> Safe Rust: memory safe, no undefined behavior possible. Unsafe Rust: can trigger undefined behavior if preconditions are violated.

So Unsafe Rust from a UB perspective is no different than C/C++. If preconditions are violated, UB can occur, affecting anywhere in the program. Its unclear how the compiler could check anything about preconditions in a block explicitly used to say that the developer is the one upholding the preconditions.

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