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Comment by biorach | Hacker News Reader

Yeah, if you need a linked list (you probably don't) use that. If however you are one of the very small number of people who need fine-grained control over a tailored data-structure with internal cross-references or whatnot then you may find yourself in a world where Rust really does not believe that you know what you are doing and fights you every step of the way. If you actually do know what you are doing, then Zig is probably the best modern choice. The TigerBeetle people chose Zig for these reasons, various resources on the net explain their motivations.

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The point with the linked list is that it is perfectly valid to use unsafe to design said ”tailored data structure with internal cross-reference or what not” library and then expose a safe interface.

If you’re having trouble designing a safe interface for your collection then that should be a signal that maybe what you are doing will result in UB when looked at the wrong way.

That is how all standard library collections in Rust works. They’ve just gone to the length of formally verifying parts of the code to ensure performance and safety.

> If you’re having trouble designing a safe interface for your collection then that should be a signal that maybe what you are doing will result in UB when looked at the wrong way.

Rust is great, but there are some things that are safe (and you could prove them safe in the abstract), but that you can't easily express in Rust's type system.

More specifically, there are some some things and usage pattern of these things that are safe when taken together. But the library can't force the safe usage pattern on the client, with the tools that Rust provides.

If you can't create a safe interface and must have the function then create an unsafe function and clearly document the invariants and then rely on the user to uphold them?

Take a look at the unsafe functions for the standard library Vec type to see examples of this:

https://doc.rust-lang.org/std/vec/struct.Vec.html#method.fro...

> If you can't create a safe interface and must have the function then create an unsafe function and clearly document the invariants and then rely on the user to uphold them?

Yes, that's what you do in practice. But it's no different--in principle--from the approach C programmers have to use.

>>That is how all standard library collections in Rust works

Yeah and that's what not going to work for high performance data structures because you need to embed hooks into the objects - not just put objects into a bigger collection object. Once you think in terms of a collection that contains things you have already lost that specific battle.

Another thing that doesn't work very well in Rust (from my understanding, I tried it very briefly) is using multiple memory allocators which is also needed in high performance code. Zig takes care to make it easy and explicit.

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