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0 pointsJoshTriplett8y ago0 comments

> Maybe forward pointer/backpointer pairs need to be a language level concept. The compiler needs to know that the forward pointer and the backpointer are in a relationship. The pair needs to be manipulated as a unit. You have to have mutable ownership of both references to manipulate either. The borrow checker and destructor ordering need to understand this.

There are many more patterns where that came from, and you don't want to teach the compiler about all of them. I don't think there's anything wrong with having a lower-level "unsafe" mechanism to let you use the language itself to build new types of structures that then provide a safe interface.

As a random example, consider the rust "intrusive-collections" crate (https://crates.io/crates/intrusive-collections), which provides the kind of "no extra pointer" linked list where you can embed a list head (or multiple list heads) directly in your structure. I don't think every such crate should have its functionality native in the compiler.

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Animats8y ago

rust "intrusive-collections" crate

People used to code like that, mostly in assembler and sometimes in C. It's not necessary for functionality. It's just an optimization. One that needs to be justified with benchmarks. Also, it's not at all clear that use of that module is safe.

I'm beginning to think there's a cult of l33t unsafe Rust programming, where people who write unsafe code think they're cool. I used to say that the way to cure new programmers of that is to put them on crash dump analysis for a few months. After they've found pointer bugs in other people's code, they'll have a better sense of why pointer safety is important.

JoshTriplettOP8y ago

> It's not necessary for functionality. It's just an optimization. One that needs to be justified with benchmarks.

I've worked with people who have the benchmarks to back it up; pointer traversals are expensive.

> people who write unsafe code think they're cool

I've tended to find the opposite: most of the Rust programmers I run into treat unsafe code as an occasionally necessary evil, and every time they write it they think about how the landscape could be improved so they wouldn't have had to, or how to encapsulate it in a separate crate with a small surface area.

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