Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::repeat_once: calling `repeat(1)` on a string literal

What it meansChecks for usage of .repeat(1) and suggest the following method for each types. .to_string() for str .clone() for String .to_vec() for slice The lint will evaluate constant expressions and values as arguments of .repeat(..) and emit a message if they are equivalent to 1. (Related discussion in rust-clippy#7306) It is in the complexity group and warns by default.

What you see

warning: calling `repeat(1)` on a string literal
 --> main.rs:2:13
  |
2 |     let x = String::from("hello world").repeat(1);
  |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `.clone()` instead: `String::from("hello world").clone()`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#repeat_once
  = note: `#[warn(clippy::repeat_once)]` 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?

For example, String.repeat(1) is equivalent to .clone(). If cloning the string is the intention behind this, clone() should be used.

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

fn main() {
    let x = String::from("hello world").repeat(1);
}

Write this instead

fn main() {
    let x = String::from("hello world").clone();
}

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
repeat_once = "allow"

One run

cargo clippy -- -A clippy::repeat-once

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

1.47.0added in Rust

Clippy's own documentation

What it does

Checks for usage of .repeat(1) and suggest the following method for each types.

.to_string() for str
.clone() for String
.to_vec() for slice

The lint will evaluate constant expressions and values as arguments of .repeat(..) and emit a message if they are equivalent to 1. (Related discussion in rust-clippy#7306)

Why is this bad?

For example, String.repeat(1) is equivalent to .clone(). If cloning the string is the intention behind this, clone() should be used.

Example

fn main() {
    let x = String::from("hello world").repeat(1);
}

Use instead:

fn main() {
    let x = String::from("hello world").clone();
}

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

Up next

Also worth your time

Did this answer your question?