Clippy lints / Style
Clippy lint · Style · checked with Clippy 0.1.99
clippy::unused_unit: unneeded unit expression
What it meansChecks for unit (()) expressions that can be removed. It is in the style group and warns by default.
What you see
warning: unneeded unit expression --> main.rs:4:5 | 4 | () | ^^ help: remove the final `()` | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#unused_unit = note: `#[warn(clippy::unused_unit)]` 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?
Such expressions add no value, but can make the code less readable. Depending on formatting they can make a break or return statement look like a function call.
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
fn return_unit() -> () {
()
}
Write this instead
fn return_unit() {}
Turn it off, or on
Allow it where it does not fit your code, as narrowly as you can:
On one item
#[allow(clippy::unused_unit)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
unused_unit = "allow"One run
cargo clippy -- -A clippy::unused-unitThe [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 unit (()) expressions that can be removed.
Why is this bad?
Such expressions add no value, but can make the code
less readable. Depending on formatting they can make a break or return
statement look like a function call.
Example
fn return_unit() -> () {
()
}
is equivalent to
fn return_unit() {}
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
- unneeded_struct_patternstruct pattern is not needed for a unit variant
- unsafe_removed_from_nameChecks for imports that remove “unsafe” from an item’s name
- unused_enumerate_indexyou seem to use `.enumerate()` and immediately discard the index
- unusual_byte_groupingsWarns if hexadecimal or binary literals are not grouped by nibble or byte
- unwrap_or_defaultChecks for usages of the following functions with an argument that constructs a default value (e.g., Default::default or String::new): unwrap_or unwrap_or_else or_insert or_insert_with
- upper_case_acronymsChecks for fully capitalized names and optionally names containing a capitalized acronym
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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