mirror of https://github.com/rust-lang/book
67 lines
3.1 KiB
Markdown
67 lines
3.1 KiB
Markdown
<!-- DO NOT EDIT THIS FILE.
|
||
|
||
This file is periodically generated from the content in the `/src/`
|
||
directory, so all fixes need to be made in `/src/`.
|
||
-->
|
||
|
||
[TOC]
|
||
|
||
## Appendix E: Editions
|
||
|
||
In Chapter 1, you saw that `cargo new` adds a bit of metadata to your
|
||
*Cargo.toml* file about an edition. This appendix talks about what that means!
|
||
|
||
The Rust language and compiler have a six-week release cycle, meaning users get
|
||
a constant stream of new features. Other programming languages release larger
|
||
changes less often; Rust releases smaller updates more frequently. After a
|
||
while, all of these tiny changes add up. But from release to release, it can be
|
||
difficult to look back and say, “Wow, between Rust 1.10 and Rust 1.31, Rust has
|
||
changed a lot!”
|
||
|
||
Every two or three years, the Rust team produces a new Rust *edition*. Each
|
||
edition brings together the features that have landed into a clear package with
|
||
fully updated documentation and tooling. New editions ship as part of the usual
|
||
six-week release process.
|
||
|
||
Editions serve different purposes for different people:
|
||
|
||
* For active Rust users, a new edition brings together incremental changes into
|
||
an easy-to-understand package.
|
||
* For non-users, a new edition signals that some major advancements have
|
||
landed, which might make Rust worth another look.
|
||
* For those developing Rust, a new edition provides a rallying point for the
|
||
project as a whole.
|
||
|
||
At the time of this writing, three Rust editions are available: Rust 2015, Rust
|
||
2018, and Rust 2021. This book is written using Rust 2021 edition idioms.
|
||
|
||
The `edition` key in *Cargo.toml* indicates which edition the compiler should
|
||
use for your code. If the key doesn’t exist, Rust uses `2015` as the edition
|
||
value for backward compatibility reasons.
|
||
|
||
Each project can opt in to an edition other than the default 2015 edition.
|
||
Editions can contain incompatible changes, such as including a new keyword that
|
||
conflicts with identifiers in code. However, unless you opt in to those
|
||
changes, your code will continue to compile even as you upgrade the Rust
|
||
compiler version you use.
|
||
|
||
All Rust compiler versions support any edition that existed prior to that
|
||
compiler’s release, and they can link crates of any supported editions
|
||
together. Edition changes only affect the way the compiler initially parses
|
||
code. Therefore, if you’re using Rust 2015 and one of your dependencies uses
|
||
Rust 2018, your project will compile and be able to use that dependency. The
|
||
opposite situation, where your project uses Rust 2018 and a dependency uses
|
||
Rust 2015, works as well.
|
||
|
||
To be clear: most features will be available on all editions. Developers using
|
||
any Rust edition will continue to see improvements as new stable releases are
|
||
made. However, in some cases, mainly when new keywords are added, some new
|
||
features might only be available in later editions. You will need to switch
|
||
editions if you want to take advantage of such features.
|
||
|
||
For more details, *The* *Edition Guide* at
|
||
*https://doc.rust-lang.org/stable/edition-guide* is a complete book about
|
||
editions that enumerates the differences between editions and explains how to
|
||
automatically upgrade your code to a new edition via `cargo fix`.
|
||
|