Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::manual_split_once: Checks for usage of str::splitn(2, _)

What it meansChecks for usage of str::splitn(2, _) It is in the complexity group and warns by default.

Does it matter?

split_once is both clearer in intent and slightly more efficient.

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 s = "key=value=add";
let (key, value) = s.splitn(2, '=').next_tuple()?;
let value = s.splitn(2, '=').nth(1)?;

let mut parts = s.splitn(2, '=');
let key = parts.next()?;
let value = parts.next()?;

Write this instead

let s = "key=value=add";
let (key, value) = s.split_once('=')?;
let value = s.split_once('=')?.1;

let (key, value) = s.split_once('=')?;

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
manual_split_once = "allow"

One run

cargo clippy -- -A clippy::manual-split-once

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

Complexitygroup

warndefault level

yesfixed by cargo clippy --fix

1.57.0added in Rust

Clippy's own documentation

What it does

Checks for usage of str::splitn(2, _)

Why is this bad?

split_once is both clearer in intent and slightly more efficient.

Example

let s = "key=value=add";
let (key, value) = s.splitn(2, '=').next_tuple()?;
let value = s.splitn(2, '=').nth(1)?;

let mut parts = s.splitn(2, '=');
let key = parts.next()?;
let value = parts.next()?;

Use instead:

let s = "key=value=add";
let (key, value) = s.split_once('=')?;
let value = s.split_once('=')?.1;

let (key, value) = s.split_once('=')?;

Limitations

The multiple statement variant currently only detects iter.next()?/iter.next().unwrap() in two separate let statements that immediately follow the splitn()

Configuration

msrv: The minimum rust version that the project supports. Defaults to the rust-version field in Cargo.toml

(default: current version)

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

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