58 lines
3.3 KiB
HTML
58 lines
3.3 KiB
HTML
<!DOCTYPE html>
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<html lang="en">
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<meta charset="UTF-8">
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<title>E - Editions</title>
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<body>
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<h2 id="appendix-e-editions"><a class="header" href="#appendix-e-editions">Appendix E: Editions</a></h2>
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<p>In Chapter 1, you saw that <code>cargo new</code> adds a bit of metadata to your
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<em>Cargo.toml</em> file about an edition. This appendix talks about what that means!</p>
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<p>The Rust language and compiler have a six-week release cycle, meaning users get
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a constant stream of new features. Other programming languages release larger
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changes less often; Rust releases smaller updates more frequently. After a
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while, all of these tiny changes add up. But from release to release, it can be
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difficult to look back and say, “Wow, between Rust 1.10 and Rust 1.31, Rust has
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changed a lot!”</p>
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<p>Every three years or so, the Rust team produces a new Rust <em>edition</em>. Each
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edition brings together the features that have landed into a clear package with
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fully updated documentation and tooling. New editions ship as part of the usual
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six-week release process.</p>
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<p>Editions serve different purposes for different people:</p>
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<ul>
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<li>For active Rust users, a new edition brings together incremental changes into
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an easy-to-understand package.</li>
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<li>For non-users, a new edition signals that some major advancements have
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landed, which might make Rust worth another look.</li>
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<li>For those developing Rust, a new edition provides a rallying point for the
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project as a whole.</li>
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</ul>
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<p>At the time of this writing, four Rust editions are available: Rust 2015, Rust
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2018, Rust 2021, and Rust 2024. This book is written using Rust 2024 edition
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idioms.</p>
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<p>The <code>edition</code> key in <em>Cargo.toml</em> indicates which edition the compiler should
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use for your code. If the key doesn’t exist, Rust uses <code>2015</code> as the edition
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value for backward compatibility reasons.</p>
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<p>Each project can opt in to an edition other than the default 2015 edition.
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Editions can contain incompatible changes, such as including a new keyword that
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conflicts with identifiers in code. However, unless you opt in to those
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changes, your code will continue to compile even as you upgrade the Rust
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compiler version you use.</p>
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<p>All Rust compiler versions support any edition that existed prior to that
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compiler’s release, and they can link crates of any supported editions
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together. Edition changes only affect the way the compiler initially parses
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code. Therefore, if you’re using Rust 2015 and one of your dependencies uses
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Rust 2018, your project will compile and be able to use that dependency. The
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opposite situation, where your project uses Rust 2018 and a dependency uses
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Rust 2015, works as well.</p>
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<p>To be clear: Most features will be available on all editions. Developers using
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any Rust edition will continue to see improvements as new stable releases are
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made. However, in some cases, mainly when new keywords are added, some new
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features might only be available in later editions. You will need to switch
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editions if you want to take advantage of such features.</p>
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<p>For more details, see <a href="https://doc.rust-lang.org/stable/edition-guide"><em>The Rust Edition Guide</em></a>. This is a
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complete book that enumerates the differences between editions and explains how
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to automatically upgrade your code to a new edition via <code>cargo fix</code>.</p>
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</body>
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</html>
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