clippy::mem_replace_with_default: replacing a value of type `T` with `T::default()`

What you see

warning: replacing a value of type `T` with `T::default()`
 --> main.rs:4:16
  |
4 | let replaced = std::mem::replace(&mut text, String::default());
  |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `std::mem::take` instead: `std::mem::take(&mut text)`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#mem_replace_with_default
  = note: `#[warn(clippy::mem_replace_with_default)]` 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?

std::mem module already has the method take to take the current value and replace it with the default value of that type.

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

let mut text = String::from("foo");
let replaced = std::mem::replace(&mut text, String::default());

Write this instead

let mut text = String::from("foo");
let taken = std::mem::take(&mut text);

Turn it off, or on

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

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

[lints.clippy]
mem_replace_with_default = "allow"

cargo clippy -- -A clippy::mem-replace-with-default

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