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Comment by emilsayahi | Hacker News Reader

I often hear this and am confused; not only are things like 'object soup'[0] possible and straightforward (putting things in collections and referring to them by indices), I never concretely hear why a graph or doubly-linked list becomes uniquely difficult to implement in Rust (and would genuinely be curious to learn why you feel this way). If you needed such data structures anyway, they're either in the standard library or in the many libraries ('crates' in Rust-lingo) available on Rust's package registry[1]---using dependencies in Rust is very straightforward & easy.

[0]: https://jacko.io/object_soup.html

[1]: https://crates.io/

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The ownership and model makes working with pointers a lot more complicated, which is the core of a good graph or doubly-linked list datatype.

> Learn Rust With Entirely Too Many Linked Lists

> In this series I will teach you basic and advanced Rust programming entirely by having you implement 6 linked lists. In doing so, you should learn:

* The following pointer types: &, &mut, Box, Rc, Arc, *const, *mut, NonNull(?)

* Ownership, borrowing, inherited mutability, interior mutability, Copy

* All The Keywords: struct, enum, fn, pub, impl, use, ...

* Pattern matching, generics, destructors

* Testing, installing new toolchains, using miri

* Unsafe Rust: raw pointers, aliasing, stacked borrows, UnsafeCell, variance

https://rust-unofficial.github.io/too-many-lists/

Object soup is like reinventing the heap, badly.

I have two different reactions to this:

- From the perspective of e.g. C++, I don't think it's reinventing the heap. We often prefer to use indexes into a std::vector or similar, even when putting everything in std::shared_ptr is an option, because the dense layout of the vector gives us the blazing fast cache performance we crave. It also avoids memory leaks from reference cycles.

- From the perspective of e.g. Python, yeah it's reinventing the heap. Unless you need to serialize the whole collection into JSON or something, it's much less convenient. But (almost) no one uses Rust instead of Python just for the convenience. (There are dozens of us! Dozens!)

One of the reasons to reach for a low level language is to have control over tradeoffs specific to your use case instead of using some pre-packaged option. Data structures are a very good example. Generic data structures like those in the standard library will likely suffice for many use cases, but a low level language must give the user the control to write their own. It’s just table stakes for this type of language.

Thankfully, rust does give you that level of control, you can write your own doubly-linked list implementation if you want, and you can pick your safety-overhead tradeoff.

Not sure about Rust std. But on cpp I heard a lot low-level companies avoid using its standard library since it is too bloated and optimized for too many cases.

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