2024 edition and its quirks

What are Editions?

In May 2015, the release of Rust 1.0 established “stability without stagnation” as a core Rust axiom. Since then, Rust has committed to a pivotal rule: once a feature is released through stable, contributors will continue to support that feature for all future releases.

However, there are times when it’s useful to make backwards-incompatible changes to the language. A common example is the introduction of a new keyword. For instance, early versions of Rust didn’t feature the async and await keywords.

If Rust had suddenly introduced these new keywords, some code would have broken: let async = 1; would no longer work.

Rust uses editions to solve this problem. When there are backwards-incompatible changes, they are pushed into the next edition. Since editions are opt-in, existing crates won’t use the changes unless they explicitly migrate into the new edition. For example, the latest version of Rust doesn’t treat async as a keyword unless edition 2018 or later is chosen.

Each crate chooses its edition within its Cargo.toml file. When creating a new crate with Cargo, it will automatically select the newest stable edition.