Clippy lints / Style
Clippy lint · Style · checked with Clippy 0.1.99
clippy::chars_next_cmp: you should use the `starts_with` method
What it meansChecks for usage of .chars().next() on a str to check if it starts with a given char. It is in the style group and warns by default.
What you see
warning: you should use the `starts_with` method --> main.rs:4:4 | 4 | if name.chars().next() == Some('_') {}; | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: like this: `name.starts_with('_')` | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#chars_next_cmp = note: `#[warn(clippy::chars_next_cmp)]` 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?
Readability, this can be written more concisely as _.starts_with(_).
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 name = "foo";
if name.chars().next() == Some('_') {};
Write this instead
let name = "foo";
if name.starts_with('_') {};
Turn it off, or on
Allow it where it does not fit your code, as narrowly as you can:
On one item
#[allow(clippy::chars_next_cmp)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
chars_next_cmp = "allow"One run
cargo clippy -- -A clippy::chars-next-cmpThe [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.
Clippy's own documentation
What it does
Checks for usage of .chars().next() on a str to check
if it starts with a given char.
Why is this bad?
Readability, this can be written more concisely as
_.starts_with(_).
Example
let name = "foo";
if name.chars().next() == Some('_') {};
Use instead:
let name = "foo";
if name.starts_with('_') {};
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
- needless_returnunneeded `return` statement
- new_without_defaultChecks for public types with a pub fn new() -> Self method and no implementation of Default
- len_zeroChecks for getting the length of something via .len() just to compare to zero, and suggests using .is_empty() where applicable
- byte_char_slicescan be more succinctly written as a byte str
- bytes_nthcalled `.bytes().nth()` on a `str`
- chars_last_cmpChecks for usage of _.chars().last() or _.chars().next_back() on a str to check if it ends with a given char
- chunks_exact_to_as_chunksusing `chunks_exact` with a constant chunk size
- cmp_nullThis lint checks for equality comparisons with ptr::null or ptr::null_mut
- collapsible_ifChecks for nested if statements which can be collapsed by &&-combining their conditions
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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