Clippy lint · Performance · checked with Clippy 0.1.99

clippy::redundant_iter_cloned: unneeded cloning of iterator items

What it meansChecks for calls to Iterator::cloned where the original value could be used instead. It is in the performance group and warns by default.

What you see

warning: unneeded cloning of iterator items
 --> main.rs:4:9
  |
4 | let _ = x.iter().cloned().map(|x| x.len());
  |         ^^^^^^^^--------------------------
  |                 |
  |                 help: try: `.map(|x| x.len())`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#redundant_iter_cloned
  = note: `#[warn(clippy::redundant_iter_cloned)]` on by default

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?

It is not always possible for the compiler to eliminate useless allocations and deallocations generated by redundant clone()s.

Code that could be written to run faster. 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 x = vec![String::new()];
let _ = x.iter().cloned().map(|x| x.len());

Write this instead

let x = vec![String::new()];
let _ = x.iter().map(|x| x.len());

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
redundant_iter_cloned = "allow"

One run

cargo clippy -- -A clippy::redundant-iter-cloned

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.

Performancegroup

warndefault level

yesfixed by cargo clippy --fix

1.92.0added in Rust

Clippy's own documentation

What it does

Checks for calls to Iterator::cloned where the original value could be used instead.

Why is this bad?

It is not always possible for the compiler to eliminate useless allocations and deallocations generated by redundant clone()s.

Example

let x = vec![String::new()];
let _ = x.iter().cloned().map(|x| x.len());

Use instead:

let x = vec![String::new()];
let _ = x.iter().map(|x| x.len());

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

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