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Rollup merge of #59456 - czipperz:for-keyword-document-higher-ranked-trait-bounds, r=Centril

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Add documentation about `for` used as higher ranked trait bounds

Resolves #55416
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Mazdak Farrokhzad 2019-03-28 08:43:40 +01:00 committed by GitHub
commit d5b8048245
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1 changed files with 12 additions and 5 deletions
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17
src/libstd/keyword_docs.rs
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@ -286,11 +286,16 @@ mod fn_keyword { }
//
/// The `for` keyword.
///
/// `for` is primarily used in for-in-loops, but it has a few other pieces of syntactic uses such as
/// `impl Trait for Type` (see [`impl`] for more info on that). for-in-loops, or to be more
/// precise, iterator loops, are a simple syntactic sugar over an exceedingly common practice
/// within Rust, which is to loop over an iterator until that iterator returns `None` (or `break`
/// is called).
/// The `for` keyword is used in many syntactic locations:
///
/// * `for` is used in for-in-loops (see below).
/// * `for` is used when implementing traits as in `impl Trait for Type` (see [`impl`] for more info
/// on that).
/// * `for` is also used for [higher-ranked trait bounds] as in `for<'a> &'a T: PartialEq<i32>`.
///
/// for-in-loops, or to be more precise, iterator loops, are a simple syntactic sugar over a common
/// practice within Rust, which is to loop over an iterator until that iterator returns `None` (or
/// `break` is called).
///
/// ```rust
/// for i in 0..5 {
@ -347,6 +352,8 @@ mod fn_keyword { }
/// For more information on for-loops, see the [Rust book] or the [Reference].
///
/// [`impl`]: keyword.impl.html
/// [higher-ranked trait bounds]:
/// https://doc.rust-lang.org/nightly/reference/trait-bounds.html#higher-ranked-trait-bounds
/// [`IntoIterator`]: iter/trait.IntoIterator.html
/// [Rust book]:
/// https://doc.rust-lang.org/book/2018-edition/ch03-05-control-flow.html#looping-through-a-collection-with-for