diff options
| -rw-r--r-- | compiler/rustc_lint/src/for_loop_over_fallibles.rs | 44 |
1 files changed, 21 insertions, 23 deletions
diff --git a/compiler/rustc_lint/src/for_loop_over_fallibles.rs b/compiler/rustc_lint/src/for_loop_over_fallibles.rs index 6870942af94..48a876b157b 100644 --- a/compiler/rustc_lint/src/for_loop_over_fallibles.rs +++ b/compiler/rustc_lint/src/for_loop_over_fallibles.rs @@ -10,43 +10,41 @@ use rustc_span::{sym, Span}; use rustc_trait_selection::traits::TraitEngineExt; declare_lint! { - /// ### What it does - /// /// Checks for `for` loops over `Option` or `Result` values. /// - /// ### Why is this bad? - /// Readability. This is more clearly expressed as an `if - /// let`. + /// ### Explanation + /// + /// Both `Option` and `Result` implement `IntoIterator` trait, which allows using them in a `for` loop. + /// `for` loop over `Option` or `Result` will iterate either 0 (if the value is `None`/`Err(_)`) + /// or 1 time (if the value is `Some(_)`/`Ok(_)`). This is not very useful and is more clearly expressed + /// via `if let`. + /// + /// `for` loop can also be accidentally written with the intention to call a function multiple times, + /// while the function returns `Some(_)`, in these cases `while let` loop should be used instead. + /// + /// The "intended" use of `IntoIterator` implementations for `Option` and `Result` is passing them to + /// generic code that expects something implementing `IntoIterator`. For example using `.chain(option)` + /// to optionally add a value to an iterator. /// /// ### Example /// /// ```rust /// # let opt = Some(1); /// # let res: Result<i32, std::io::Error> = Ok(1); - /// for x in opt { - /// // .. - /// } - /// - /// for x in &res { - /// // .. - /// } - /// - /// for x in res.iter() { - /// // .. - /// } + /// # let recv = || Some(1); + /// for x in opt { /* ... */} + /// for x in res { /* ... */ } + /// for x in recv() { /* ... */ } /// ``` /// /// Use instead: /// ```rust /// # let opt = Some(1); /// # let res: Result<i32, std::io::Error> = Ok(1); - /// if let Some(x) = opt { - /// // .. - /// } - /// - /// if let Ok(x) = res { - /// // .. - /// } + /// # let recv = || Some(1); + /// if let Some(x) = opt { /* ... */} + /// if let Ok(x) = res { /* ... */ } + /// while let Some(x) = recv() { /* ... */ } /// ``` pub FOR_LOOP_OVER_FALLIBLES, Warn, |