Missing Clone for Box

[douglas-raillard-arm]

Bumpalo's Box is missing a Clone implementation, which is a pretty big departure from std's Box. Bringing it back would require storing a &Bump inside the Box in addition to the &mut T to be able to allocate a new value inside the same arena.

That is also the way std is implemented:
https://doc.rust-lang.org/src/alloc/boxed.rs.html#198-201

[fitzgen]

This was intentional to keep bumpalo::boxed::Box a single word.

[douglas-raillard-arm]

Maybe that could become opt-in with a generic parameter, defaulting to current behavior ? Something like:

pub struct Box<'a, T: ?Sized, Alloc=()>(&'a mut T, alloc: Alloc);

type CloneableBox<'a, T> = Box<'a, T, &'a Bump>;

impl<'a, T: ?Sized> Clone for Box<'a, T, &'a Bump> {
      ...
}

[rzvxa]

In oxc, we achieve this with a CloneIn trait.

https://github.com/oxc-project/oxc/blob/main/crates/oxc_allocator/src/clone_in.rs something similar might be useful to you.