Clippy lints / Pedantic
Clippy lint · Pedantic · checked with Clippy 0.1.99
clippy::needless_for_each: needless use of `for_each`
What it meansChecks for usage of for_each that would be more simply written as a for loop. It is in the pedantic group and off by default.
What you see
warning: needless use of `for_each` --> main.rs:4:1 | 4 | / v.iter().for_each(|elem| { 5 | | println!("{elem}"); 6 | | }) | |__^ | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#needless_for_each = note: `-W clippy::needless-for-each` implied by `-W clippy::pedantic` help: try | 4 + for elem in v.iter() { 5 + println!("{elem}"); 6 + } |
Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.
Does it matter?
for_each may be used after applying iterator transformers like filter for better readability and performance. It may also be used to fit a simple operation on one line. But when none of these apply, a simple for loop is more idiomatic.
Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.
How to fix it
Clippy can fix this one for you: run cargo clippy --fix (add --allow-dirty if you have uncommitted changes). Review the diff before you commit.
Flagged
let v = vec![0, 1, 2];
v.iter().for_each(|elem| {
println!("{elem}");
})
Write this instead
let v = vec![0, 1, 2];
for elem in &v {
println!("{elem}");
}
Turn it off, or on
It is off by default. To use it, set it to warn or deny:
Whole crate (Cargo.toml)
[lints.clippy]
needless_for_each = "warn"In code
#![warn(clippy::needless_for_each)]One run
cargo clippy -- -W clippy::needless-for-eachThe [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.
Clippy's own documentation
What it does
Checks for usage of for_each that would be more simply written as a
for loop.
Why is this bad?
for_each may be used after applying iterator transformers like
filter for better readability and performance. It may also be used to fit a simple
operation on one line.
But when none of these apply, a simple for loop is more idiomatic.
Example
let v = vec![0, 1, 2];
v.iter().for_each(|elem| {
println!("{elem}");
})
Use instead:
let v = vec![0, 1, 2];
for elem in &v {
println!("{elem}");
}
Known Problems
When doing things such as:
let v = vec![0, 1, 2];
v.iter().for_each(|elem| unsafe {
libc::printf(c"%d\n".as_ptr(), elem);
});
This lint will not trigger.
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
- too_many_linesChecks for functions with a large amount of lines
- missing_errors_docChecks the doc comments of publicly visible functions that return a Result type and warns if there is no # Errors section
- must_use_candidateChecks for public functions that have no #[must_use] attribute, but return something not already marked must-use, have no mutable arg and mutate no statics
- naive_bytecountChecks for naive byte counts
- needless_bitwise_booluse of bitwise operator instead of lazy operator between booleans
- needless_continueThe lint checks for if-statements appearing in loops that contain a continue statement in either their main blocks or their else-blocks, when omitting the else-block possibly with some rearrangement of code can make the code easier to understand. The lint also checks if the last statement in the loop is a continue
- needless_pass_by_valuethis argument is passed by value, but not consumed in the function body
- needless_raw_string_hashesunnecessary hashes around raw string literal
- no_effect_underscore_bindingbinding to `_` prefixed variable with no side-effect
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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