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by asa400 844 days ago
> My experience with snare and pizauth is that Rust is a viable language for writing daemons in. Rust isn’t a perfect language (e.g. unsafe Rust currently has no meaningful semantics so any code which uses unsafe comes with fewer guarantees than C)

What exactly does the author mean when they say that unsafe Rust has "no meaningful semantics"? Is this a term of art in language analysis or is the author just saying "it's weird"?
3 comments
ltratt 844 days ago
As an example, I like to point people at https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html which for many years now has contained this line:

> The precise Rust aliasing rules are somewhat in flux, but the main points are not contentious

I've sometimes found myself in situations where the only way I've been able to deal with this is to check the compiler's output and trawl forums for hints by Rust's developers about what they think/hope the semantics are/will be.

Historically speaking, this situation isn't uncommon: working out exactly what a language's semantics should be is hard, particularly when it has many novel aspects. Most major languages go through this sort of sequence. Some sooner or later than others --- and some end up addressing it more thoroughly than others). Eventually I expect Rust to develop something similar to the modern C spec, but we're not there yet.

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asa400 844 days ago
Excellent - thank you for the example and the clarification. This is exactly what I was looking for.
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zokier 844 days ago
Rust as a language is in practice defined as whatever rustc does, there is no authorative specification like ISO C standard
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viraptor 843 days ago
It's a weird claim. See https://doc.rust-lang.org/book/ch19-01-unsafe-rust.html

> It’s important to understand that unsafe doesn’t turn off the borrow checker or disable any other of Rust’s safety checks: if you use a reference in unsafe code, it will still be checked. The unsafe keyword only gives you access to these five features that are then not checked by the compiler for memory safety.

Fully defined rust or not, unsafe code blocks definitely do not have fewer guarantees than C.

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