It's not part of std exactly, it's part of alloc. It's re-exported by std. It would still be available in a #![no_std] environment using `extern crate alloc`.

It's not part of std exactly, it's part of alloc. It's re-exported by std. It would still be available in a #![no_std] environment using `extern crate alloc`. This crate generally abstracts over the concept of allocation too, so relying on it doesn't require you to also have an allocator - it just requires someone at some point specify one with #[global_allocator]