diff --git a/src/libstd/keyword_docs.rs b/src/libstd/keyword_docs.rs index a62987891b9..fdb4c7d599c 100644 --- a/src/libstd/keyword_docs.rs +++ b/src/libstd/keyword_docs.rs @@ -1060,9 +1060,50 @@ mod pub_keyword {} // /// Bind by reference during pattern matching. /// -/// The documentation for this keyword is [not yet complete]. Pull requests welcome! +/// `ref` annotates pattern bindings to make them borrow rather than move. +/// It is **not** a part of the pattern as far as matching is concerned: it does +/// not affect *whether* a value is matched, only *how* it is matched. /// -/// [not yet complete]: https://github.com/rust-lang/rust/issues/34601 +/// By default, [`match`] statements consume all they can, which can sometimes +/// be a problem, when you don't really need the value to be moved and owned: +/// +/// ```compile_fail,E0382 +/// let maybe_name = Some(String::from("Alice")); +/// // The variable 'maybe_name' is consumed here ... +/// match maybe_name { +/// Some(n) => println!("Hello, {}", n), +/// _ => println!("Hello, world"), +/// } +/// // ... and is now unavailable. +/// println!("Hello again, {}", maybe_name.unwrap_or("world".into())); +/// ``` +/// +/// Using the `ref` keyword, the value is only borrowed, not moved, making it +/// available for use after the [`match`] statement: +/// +/// ``` +/// let maybe_name = Some(String::from("Alice")); +/// // Using `ref`, the value is borrowed, not moved ... +/// match maybe_name { +/// Some(ref n) => println!("Hello, {}", n), +/// _ => println!("Hello, world"), +/// } +/// // ... so it's available here! +/// println!("Hello again, {}", maybe_name.unwrap_or("world".into())); +/// ``` +/// +/// # `&` vs `ref` +/// +/// - `&` denotes that your pattern expects a reference to an object. Hence `&` +/// is a part of said pattern: `&Foo` matches different objects than `Foo` does. +/// +/// - `ref` indicates that you want a reference to an unpacked value. It is not +/// matched against: `Foo(ref foo)` matches the same objects as `Foo(foo)`. +/// +/// See also the [Reference] for more information. +/// +/// [`match`]: keyword.match.html +/// [Reference]: ../reference/patterns.html#identifier-patterns mod ref_keyword {} #[doc(keyword = "return")]