RS.CLIPPY.MAP_FLATTEN

Using combinations of `flatten` and `map` which can usually be written as a single method call

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

What it does

Checks for usage of _.map(_).flatten(_) on Iterator and Option

Why is this bad?

Readability, this can be written more concisely as _.flat_map(_) for Iterator or _.and_then(_) for Option

Example

let vec = vec![vec![1]];
let opt = Some(5);

vec.iter().map(|x| x.iter()).flatten();
opt.map(|x| Some(x * 2)).flatten();

Use instead:

vec.iter().flat_map(|x| x.iter());
opt.and_then(|x| Some(x * 2));