[jeroenhd]

> If the type allocates its own behind the scenes, I can't do that.

Isn't that the reason why Zig passes around allocators everywhere? If you're using a buffer pool, you should probably be handing out some kind of buffer pool allocator.

Requiring all allocation to have happened before execution is still a good reason to pass buffers around, but I feel like the other situations you describe can be solved by just passing the right allocators.