I know next to nothing about rust, but can't you do pretty much whatever you want when you implement a custom allocator? Including allocate a giant buffer ahead of time and reuse stuff with no safety whatsoever?
I'm not sure custom allocators exist. But assuming they did, sure you can. But in that case you're explicitly opting into unsafe code to use uninitialized memory.
And, even if you did have such an allocator, you still can't read past the end of the allocation. So if you ask for a 16 byte buffer and attempt to read 17, it'll fail.
