clippy::manual_is_power_of_two: manually reimplementing `is_power_of_two`

What you see

warning: manually reimplementing `is_power_of_two`
 --> main.rs:4:14
  |
4 | let result = a.count_ones() == 1;
  |              ^^^^^^^^^^^^^^^^^^^ help: consider using `.is_power_of_two()`: `a.is_power_of_two()`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#manual_is_power_of_two
  = note: `-W clippy::manual-is-power-of-two` implied by `-W clippy::pedantic`

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?

Manual reimplementations of is_power_of_two increase code complexity for little benefit.

Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.

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 a: u32 = 4;
let result = a.count_ones() == 1;

Write this instead

let a: u32 = 4;
let result = a.is_power_of_two();

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

[lints.clippy]
manual_is_power_of_two = "warn"

#![warn(clippy::manual_is_power_of_two)]

cargo clippy -- -W clippy::manual-is-power-of-two

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