bumpalo

Long story short, heap allocation is painfully slow. Any sort of malloc will always be slower than a custom pool or a bump allocator, because it has a lot more context to deal with. Rust makes it especially hard to use custom allocators, see bumpalo for example [0]. To be fair, progress is being made in this area [1]. Theoretically one can use a "handle table" as a replacement for pools, you can find relevant discussion at [2]. [0] https://github.com/fitzgen/bumpalo [1] https://github.com/rust-lang/rust/issues/32838 [2] https://news.ycombinator.com/item?id=36353145 Edit: formatting.

TSC doesn't need to "stick around", right? Just a run-once and the program is over? In those cases, https://github.com/fitzgen/bumpalo works amazingly as an arena. You can pretty much forget about reference counting and have direct references everywhere in your graph. The disadvantage is that it's hard to modify your tree without leaving memory around. We use it extensively in http://github.com/dioxusLabs/dioxus and don't need to worry about Rc anywhere in the graph/diffing code.

Rust has an arena allocator too[1], but it is implemented with 165(!!!) usages of unsafe. :) [1] https://github.com/fitzgen/bumpalo

Crates like https://crates.io/crates/typed-arena and https://github.com/fitzgen/bumpalo are the way you do this in today’s Rust, but what he’s referring to is that types like String manage their own allocations and aren’t yet parameterizable by an allocator. So they’re not super easy to use together. In my experience most of the time you need arenas you’re using your own data structure anyway, but YMMV.

In Zig, as far as I understand, you really just pass an allocator around. I don't see any special syntax to support this? This could be done in Rust. There is, for example, the simple bump allocator bumpalo [1]. It would be nice if the the std collections supported this (in planning, but hasn't seen much progress), and most dependencies would not be built around a manually passed allocator. > Rust assumes most of the time you'll be passing around references to values or small structures allocated on the stack. Can you clarify what you mean here? All of the std collections (Vec, HashMap, etc) use allocation. There are also `Box`, `Rc` and `Arc`, which allocate and are used everywhere. [1] https://github.com/fitzgen/bumpalo

Check out bumpalo[1]. Dodrio is a real-world[2] usage of bumpalo, so you can inspect that code to see how he deals with lifetimes correctly. Edit: GATs are how "placement new" (Rust doesn't have new at all, hence the airquotes) would work in Rust, assuming the author here meant to say "custom allocators." With GATs, you could create a pointer (Box, Arc, ArenaBox etc.) trait and use that on your message types.[3] "Placement new" is a whole different issue that ultimately boils down to a compiler optimization that is currently missing/not working and shouldn't functionally affect what you are trying to do at all. [1]: https://github.com/fitzgen/bumpalo [2]: https://github.com/fitzgen/dodrio [3]: https://rust-lang.github.io/rfcs/1598-generic_associated_typ...

You can implement an allocator in Rust; it's unclear why you think this is not possible. One example: - https://github.com/fitzgen/bumpalo