Clippy lint · Style · checked with Clippy 0.1.99

clippy::manual_while_let_some: you seem to be trying to pop elements from a `Vec` in a loop

What it meansLooks for loops that check for emptiness of a Vec in the condition and pop an element in the body as a separate operation. It is in the style group and warns by default.

What you see

warning: you seem to be trying to pop elements from a `Vec` in a loop
 --> main.rs:5:5
  |
5 |     let number = numbers.pop().unwrap();
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#manual_while_let_some
  = note: `#[warn(clippy::manual_while_let_some)]` on by default
help: consider using a `while..let` loop
  |
4 ~ while let Some(number) = numbers.pop() {
5 ~     
  |

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?

Such loops can be written in a more idiomatic way by using a while-let loop and directly pattern matching on the return value of Vec::pop().

Code that works but is not idiomatic Rust. 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 mut numbers = vec![1, 2, 3, 4, 5];
while !numbers.is_empty() {
    let number = numbers.pop().unwrap();
    // use `number`
}

Write this instead

let mut numbers = vec![1, 2, 3, 4, 5];
while let Some(number) = numbers.pop() {
    // use `number`
}

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
manual_while_let_some = "allow"

One run

cargo clippy -- -A clippy::manual-while-let-some

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.

Stylegroup

warndefault level

yesfixed by cargo clippy --fix

1.71.0added in Rust

Clippy's own documentation

What it does

Looks for loops that check for emptiness of a Vec in the condition and pop an element in the body as a separate operation.

Why is this bad?

Such loops can be written in a more idiomatic way by using a while-let loop and directly pattern matching on the return value of Vec::pop().

Example

let mut numbers = vec![1, 2, 3, 4, 5];
while !numbers.is_empty() {
    let number = numbers.pop().unwrap();
    // use `number`
}

Use instead:

let mut numbers = vec![1, 2, 3, 4, 5];
while let Some(number) = numbers.pop() {
    // use `number`
}

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

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