Lint against Iterator::map receiving a callable that returns () #106991
Description
Code
fn foo(items: &mut Vec<u8>){ items.sort(); } fn main() { let mut x: Vec<Vec<u8>> = vec![ vec![0, 2, 1], vec![5, 4, 3], ]; x.iter_mut().map(foo); println!("{x:?}"); }Current output
PassesDesired output
warning: `Iterator::map` call that discard the iterator's values | LL | fn foo(items: &mut Vec<u8>) { | --- this function returns `()`, which is likely not what you wanted ... LL | x.iter_mut().map(foo) | --- ^^^ called `Iterator::map` with callable that returns `()` | | | after this call to map, the resulting iterator is `impl Iterator<Item = ()>`, which means the only information carried by the iterator is the number of items | = note: `Iterator::map`, like many of the methods on `Iterator`, gets executed lazily, meaning that its effects won't be visible until it is iterated help: you might have meant to use `Iterator::for_each` | LL - x.iter_mut().map(foo) LL + x.iter_mut().for_each(foo) |Rationale and extra context
Mapping to () is almost always a mistake. The for_each suggestion should only be emitted if it would make sense with foo, like if it modifies the argument or has side-effects like printing or logging (the later would be hard to check for).
Other cases
No response
Anything else?
No response