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0 pointsReelin6y ago0 comments

> The only way to drop an extensively nested structure like this any faster than traversing it would be an arena allocator, and forgetting about the entire arena.

Isn't that incompatible with RAII though?

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4 comments · 2 top-level

arcticbull6y ago· 2 in thread

You can handle this in Rust pretty neatly with lifetimes. There's a bunch of crates that do this. [1]

[1] https://crates.io/crates/typed-arena

ReelinOP6y ago

That's a neat library but as far as I can tell it doesn't avoid any traversal or cleanup code. It appears to delay the cleanup so it all happens at once. That's certainly useful, but if you have RAII the traversal still has to happen at some point.

winstonewert6y ago

It avoids it if your type has no-op drop implementation. So if you use typed-arena for objects which don't own resources, they all get dropped in one massive deallocation and don't have to be traversed.

EDIT: and then I noticed that you mentioned RAII... Right, if the object own some sort of resources that doesn't apply.

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all-fakes6y ago

Yes. Some libraries, like typed-arena (and Rust's built-in Vec), will traverse the structure and call the drop implementations, and others, like bumpalo, will just leak the resources.

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