clippy::mem_replace_option_with_none: replacing an `Option` with `None`

What you see

warning: replacing an `Option` with `None`
 --> main.rs:6:16
  |
6 | let replaced = mem::replace(&mut an_option, None);
  |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `Option::take()` instead: `an_option.take()`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#mem_replace_option_with_none
  = note: `#[warn(clippy::mem_replace_option_with_none)]` 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?

Option already has the method take() for taking its current value (Some(..) or None) and replacing it with None.

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

use std::mem;

let mut an_option = Some(0);
let replaced = mem::replace(&mut an_option, None);

Write this instead

let mut an_option = Some(0);
let taken = an_option.take();

Turn it off, or on

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

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

[lints.clippy]
mem_replace_option_with_none = "allow"

cargo clippy -- -A clippy::mem-replace-option-with-none

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.