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Comment by Rusky | Hacker News Reader

You can explain this sort of pattern to the borrow checker quite trivially: slap a single `'arena` lifetime on all the references that point to something in that arena. This pattern is used all over the place, including rustc itself.

(To be clear I agree that this is an easy pattern to write correctly without a borrow checker as well. It's just not a good example of something that's any harder to do in Rust, either.)

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I remember having multiple issues doing this in rust, but can't recall the details. Are you sure I would just be able to have whatever refs I want and use them without the borrow checker complaining about things that are actually perfectly safe? I don't remember that being the case.

Edit: reading wavemode comment above "Namely, in Rust it is undefined behavior for multiple mutable references to the same data to exist, ever. And it is also not enough for your program to not create multiple mut - the compiler also has to be able to prove that it can't." that I think was at least one of the problems I had.

The main issue with using arenas in Rust right now is that the standard library collections use the still-unstable allocator API, so you cannot use those with them. However, this is a systems language, so you can use whatever you want for your own data structures.

> reading wavemode comment above

This is true for `&mut T` but that isn't directly related to arenas. Furthermore, you can have multiple mutable aliased references, but you need to not use `&mut T` while doing so: you can take advantage of some form of internal mutability and use `&T`, for example. What is needed depends on the circumstances.

wavemode's comment only applies to `&mut T`. You do not have to use `&mut T` to form the reference graph in your arena, which indeed would be unlikely to work out.

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