clippy::manual_clear: truncating to zero length

What you see

warning: truncating to zero length
 --> main.rs:4:1
  |
4 | v.truncate(0);
  | ^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#manual_clear
  = note: `#[warn(clippy::manual_clear)]` on by default
help: use `clear()` instead
  |
4 - v.truncate(0);
4 + v.clear();
  |

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?

clear() expresses the intent better and is likely to be more efficient than truncate(0).

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 v = vec![1, 2, 3];
v.truncate(0);

Write this instead

let mut v = vec![1, 2, 3];
v.clear();

Turn it off, or on

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

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

[lints.clippy]
manual_clear = "allow"

cargo clippy -- -A clippy::manual-clear

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.