clippy::manual_retain: this expression can be written more simply using `.retain()`

What you see

warning: this expression can be written more simply using `.retain()`
 --> main.rs:4:1
  |
4 | vec = vec.iter().filter(|&x| x % 2 == 0).copied().collect();
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider calling `.retain()` instead: `vec.retain(|x| x % 2 == 0)`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#manual_retain
  = note: `#[warn(clippy::manual_retain)]` 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?

.retain() is simpler and avoids needless allocation.

Code that could be written to run faster. 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 vec = vec![0, 1, 2];
vec = vec.iter().filter(|&x| x % 2 == 0).copied().collect();
vec = vec.into_iter().filter(|x| x % 2 == 0).collect();

Write this instead

let mut vec = vec![0, 1, 2];
vec.retain(|x| x % 2 == 0);
vec.retain(|x| x % 2 == 0);

Turn it off, or on

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

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

[lints.clippy]
manual_retain = "allow"

cargo clippy -- -A clippy::manual-retain

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.

Settings in clippy.toml

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