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Comment by delamon | Hacker News Reader

They don't play nicely with arena allocators. And arenas is what you reach for if you have clear lifetime bounds: e.g. a single request with arena never de-allocates individual objects, nukes arena when done. That gives you an easy verifiable protection against leaks, data (and cache) locality and deallocation that cost zero cpu cycles.

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Rust supports arena allocator https://docs.rs/bumpalo/latest/bumpalo/ and the dropping plays well with arena as long as you use bumpalo::boxed::Box

It's technically possible to perform arena-based allocation and still have compiler checks. The compiler just need to track objects allocated with an allocator and prevent destructing the allocator itself as long as there is at least one object using it.

It's like view span objects in rust. The compiler knowns that a span is logically connected to the parent object and don't allow destroying it when such span exists.

Why not though?

Have a boxed object have implemented drop, then when the box leaves some scope the Box will clean up it's stuff (drop implementation if there is any) and deallocate it's memory using the allocator (which the arena will treat as noop).

Yes, that would work. But you would need to carry pointer to allocator inside box and it is extra code to run for every object.

extra code meaning the drop implementation or something else?

Yes, I mean the code in the drop implementation.

it isn't really overhead, assuming you don't forget defer ... accidentally

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