Clippy lint · Suspicious · checked with Clippy 0.1.99

clippy::single_range_in_vec_init: an array of `Range` that is only one element

What it meansChecks for Vec or array initializations that contain only one range. It is in the suspicious group and warns by default.

What you see

warning: an array of `Range` that is only one element
 --> main.rs:3:9
  |
3 | let x = [0..200];
  |         ^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#single_range_in_vec_init
  = note: `#[warn(clippy::single_range_in_vec_init)]` on by default
help: if you wanted a `Vec` that contains the entire range, try
  |
3 - let x = [0..200];
3 + let x = (0..200).collect::<std::vec::Vec<i32>>();
  |
help: if you wanted an array of len 200, try
  |
3 - let x = [0..200];
3 + let x = [0; 200];
  |

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?

This is almost always incorrect, as it will result in a Vec that has only one element. Almost always, the programmer intended for it to include all elements in the range or for the end of the range to be the length instead.

Code that is most likely wrong or useless. Warns by default.

How to fix it

Clippy does not fix this one automatically (its suggestion may change behaviour, so it only shows it). Change the code by hand:

Flagged

let x = [0..200];

Write this instead

// If it was intended to include every element in the range...
let x = (0..200).collect::<Vec<i32>>();
// ...Or if 200 was meant to be the len
let x = [0; 200];

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_range_in_vec_init)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
single_range_in_vec_init = "allow"

One run

cargo clippy -- -A clippy::single-range-in-vec-init

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.

Suspiciousgroup

warndefault level

nofixed by cargo clippy --fix

1.72.0added in Rust

Clippy's own documentation

What it does

Checks for Vec or array initializations that contain only one range.

Why is this bad?

This is almost always incorrect, as it will result in a Vec that has only one element. Almost always, the programmer intended for it to include all elements in the range or for the end of the range to be the length instead.

Example

let x = [0..200];

Use instead:

// If it was intended to include every element in the range...
let x = (0..200).collect::<Vec<i32>>();
// ...Or if 200 was meant to be the len
let x = [0; 200];

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

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