Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::needless_as_bytes: needless call to `as_bytes`

What it meansIt detects useless calls to str::as_bytes() before calling len() or is_empty(). It is in the complexity group and warns by default.

What you see

warning: needless call to `as_bytes`
 --> main.rs:3:11
  |
3 | let len = "some string".as_bytes().len();
  |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: `len()` can be called directly on strings: `"some string".len()`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#needless_as_bytes
  = note: `#[warn(clippy::needless_as_bytes)]` 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?

The len() and is_empty() methods are also directly available on strings, and they return identical results. In particular, len() on a string returns the number of bytes.

Code that does something simple in a complicated way. 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 len = "some string".as_bytes().len();
let b = "some string".as_bytes().is_empty();

Write this instead

let len = "some string".len();
let b = "some string".is_empty();

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
needless_as_bytes = "allow"

One run

cargo clippy -- -A clippy::needless-as-bytes

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.

Complexitygroup

warndefault level

yesfixed by cargo clippy --fix

1.84.0added in Rust

Clippy's own documentation

What it does

It detects useless calls to str::as_bytes() before calling len() or is_empty().

Why is this bad?

The len() and is_empty() methods are also directly available on strings, and they return identical results. In particular, len() on a string returns the number of bytes.

Example

let len = "some string".as_bytes().len();
let b = "some string".as_bytes().is_empty();

Use instead:

let len = "some string".len();
let b = "some string".is_empty();

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

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