Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::single_element_loop: for loop over a single element

What it meansChecks whether a for loop has a single element. It is in the complexity group and warns by default.

What you see

warning: for loop over a single element
 --> main.rs:4:1
  |
4 | / for item in &[item1] {
5 | |     println!("{}", item);
6 | | }
  | |_^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#single_element_loop
  = note: `#[warn(clippy::single_element_loop)]` on by default
help: try
  |
4 + {
5 +     let item = &item1;
6 +     println!("{}", item);
7 + }
  |

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?

There is no reason to have a loop of a single element.

Code that does something simple in a complicated way. Warns by default.

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 item1 = 2;
for item in &[item1] {
    println!("{}", item);
}

Write this instead

let item1 = 2;
let item = &item1;
println!("{}", item);

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

On one item

#[allow(clippy::single_element_loop)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
single_element_loop = "allow"

One run

cargo clippy -- -A clippy::single-element-loop

The [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.

Complexitygroup

warndefault level

yesfixed by cargo clippy --fix

1.49.0added in Rust

Clippy's own documentation

What it does

Checks whether a for loop has a single element.

Why is this bad?

There is no reason to have a loop of a single element.

Example

let item1 = 2;
for item in &[item1] {
    println!("{}", item);
}

Use instead:

let item1 = 2;
let item = &item1;
println!("{}", item);

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

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