Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::while_let_loop: this loop could be written as a `while let` loop

What it meansDetects loop + match combinations that are easier written as a while let loop. It is in the complexity group and warns by default.

What you see

warning: this loop could be written as a `while let` loop
  --> main.rs:4:1
   |
 4 | / loop {
 5 | |     let x = match y {
 6 | |         Some(x) => x,
 7 | |         None => break,
...  |
10 | | }
   | |_^ help: try: `while let Some(x) = y { .. }`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#while_let_loop
   = note: `#[warn(clippy::while_let_loop)]` 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?

The while let loop is usually shorter and more readable.

Code that does something simple in a complicated way. 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 y = Some(1);
loop {
    let x = match y {
        Some(x) => x,
        None => break,
    };
    // ..
}

Write this instead

let y = Some(1);
while let Some(x) = y {
    // ..
};

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
while_let_loop = "allow"

One run

cargo clippy -- -A clippy::while-let-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

nofixed by cargo clippy --fix

pre 1.29.0added in Rust

Clippy's own documentation

What it does

Detects loop + match combinations that are easier written as a while let loop.

Why is this bad?

The while let loop is usually shorter and more readable.

Example

let y = Some(1);
loop {
    let x = match y {
        Some(x) => x,
        None => break,
    };
    // ..
}

Use instead:

let y = Some(1);
while let Some(x) = y {
    // ..
};

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

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