RS.CLIPPY.MANUAL_FLATTEN

For loops over `Option`s or `Result`s with a single expression can be simplified

This checker is a Clippy lint created by The Rust Project Contributors. The documentation shown here is a copy of the original documentation for: manual_flatten. Copyright ©2025 The Rust Team. All rights reserved.

What it does

Checks for unnecessary if let usage in a for loop where only the Some or Ok variant of the iterator element is used.

Why is this bad?

It is verbose and can be simplified by first calling the flatten method on the Iterator.

Example

let x = vec![Some(1), Some(2), Some(3)];
for n in x {
    if let Some(n) = n {
        println!("{}", n);
    }
}

Use instead:

let x = vec![Some(1), Some(2), Some(3)];
for n in x.into_iter().flatten() {
    println!("{}", n);
}

Configuration

msrv: The minimum rust version that the project supports. Defaults to the rust-version field in Cargo.toml

(default: current version)