Clippy lints / Style
Clippy lint · Style · checked with Clippy 0.1.99
clippy::unnecessary_owned_empty_strings: usage of `&String::new()` for a function expecting a `&str` argument
What it meansDetects cases of owned empty strings being passed as an argument to a function expecting &str It is in the style group and warns by default.
What you see
warning: usage of `&String::new()` for a function expecting a `&str` argument --> main.rs:3:26 | 3 | vec!["1", "2", "3"].join(&String::new()); | ^^^^^^^^^^^^^^ help: try: `""` | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#unnecessary_owned_empty_strings = note: `#[warn(clippy::unnecessary_owned_empty_strings)]` 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?
This results in longer and less readable code
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
vec!["1", "2", "3"].join(&String::new());
Write this instead
vec!["1", "2", "3"].join("");
Turn it off, or on
Allow it where it does not fit your code, as narrowly as you can:
On one item
#[allow(clippy::unnecessary_owned_empty_strings)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
unnecessary_owned_empty_strings = "allow"One run
cargo clippy -- -A clippy::unnecessary-owned-empty-stringsThe [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
Detects cases of owned empty strings being passed as an argument to a function expecting &str
Why is this bad?
This results in longer and less readable code
Example
vec!["1", "2", "3"].join(&String::new());
Use instead:
vec!["1", "2", "3"].join("");
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
- unnecessary_lazy_evaluationsunnecessary closure used to substitute value for `Option::None`
- unnecessary_map_orthis `map_or` can be simplified
- unnecessary_mut_passedDetects passing a mutable reference to a function that only requires an immutable reference
- 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
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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