The alloc crate - The Edition Guide

# The alloc crate

Initially added:

Before 1.36.0, the standard library consisted of the crates `std`, `core`, and `proc_macro`. The `core` crate provided core functionality such as `Iterator` and `Copy` and could be used in `#![no_std]` environments since it did not impose any requirements. Meanwhile, the `std` crate provided types like `Box<T>` and OS functionality but required a global allocator and other OS capabilities in return.

Starting with Rust 1.36.0, the parts of `std` that depend on a global allocator, e.g. `Vec<T>`, are now available in the `alloc` crate. The `std` crate then re-exports these parts. While `#![no_std]` binaries using `alloc` still require nightly Rust, `#![no_std]` library crates can use the `alloc` crate in stable Rust. Meanwhile, normal binaries, without `#![no_std]`, can depend on such library crates. We hope this will facilitate the development of a `#![no_std]` compatible ecosystem of libraries prior to stabilizing support for `#![no_std]` binaries using `alloc`.

If you are the maintainer of a library that only relies on some allocation primitives to function, consider making your library `#[no_std]` compatible by using the following at the top of your `lib.rs` file:

    #![no_std]

    extern crate alloc;

    use alloc::vec::Vec;